Crust thick enough to prevent volcanos

Crust thick enough to prevent volcanos

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Could you have an Earth-like planet with a crust thick enough to prevent volcanos from forming?

Depends on how Earth-like you want it to be. On Earth, most parts of the crust do not support volcanoes. But because we have active plate tectonics, there will always be places where plates slide beneath each other (subduction zones) or where they slide apart. Volcanoes are unavoidable in these locations, I think. A planet without plate tectonics could be volcano-free, but perhaps not for the entirety of its history. Mars has no active volcanoes, but it used to; it's lost much of its internal heat since then.

It depends on the definition of Earth-like planet.

In terms of size, density and gravity Venus is very Earth-like, but in terms of atmospheric and surface conditions and its axis of rotation, and period of rotation Venus in not Earth-like.

I will assume you mean a terrestrial or rocky planet similar in size to Earth.

Earth's crust has two subdivision: oceanic and continental. Oceanic crust is between 5 km and 10 km thick whereas continental crust is between 30 km and 50 km thick:

Oceanic: 5 km (3 mi) to 10 km (6 mi) thick and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro.

Continental: 30 km (20 mi) to 50 km (30 mi) thick and mostly composed of less dense, more felsic rocks, such as granite.

Earth's crust is fractured into plates as described by plate tectonics. The boundaries of some plate collide causing uplift in the collision zone. The Himalayas is an example of such a zone. At other boundaries one plate subducts underneath the other plate. It's at these boundaries that most of Earth's volcanoes form.

For plate tectonics to occurs large amounts of water must be present to lubricate the subducting plate. The implication of this is that for plate tectonics to occur large oceans need to be located near subduction zones.

The other type of volcanoes that can occur are intraplate volcanoes which are located far from tectonic plate boundaries in the interior of tectonic plates. Such volcanoes are thought to arise from mantle plumes.

Earth has a diameter of 12 740 km, and Mars has diameter of 6780 km. The crust thickness of both planets is 5-50 km for Earth and 10-50 km for Mars. The ration of maximum crust thickness to diameter for both planets is 0.003925 for Earth and 0.007375 for Mars. The ratio for Mars is nearly double that of Earth, yet the Olympus Mons volcano on Mars is larger than any volcano on Earth.

For volcanoes to form, the temperature of the magma must be high enough to melt a hole through the crust and the pressure within the magma chamber must be high enough to overcome the resistance to flow posed by the friction of walls the volcanic vent and the gravity of the planet.

All terrestrial planets will experience volcanism at some period during their formation, it is a matter of when volcanism stops and why. Volcanism on Mercury ceased early due to the planet contracting early in it formation. Even the Moon experienced volcanism.

Crust thick enough to prevent volcanos - Astronomy

Lesson 4) A Somewhat Solid Foundation

Professor Gagarina stands at the head of the class as the students enter. On her desk is a large globe of the Earth with a sizeable chunk missing and a cracked and broken lunascope. On the walls are posters showing strange diagrams, volcanic eruptions, and a damaged city.

Hell on Earth

Let us turn our focus more firmly onto planet Earth. Heat and pressure generated by the mass of accreted rock and dust were joined by heat created from heavy asteroid impacts. Instead of solid ground, the surface of the Earth was a comparatively thin, cooled sheet of rock broken everywhere by volcanos. This volcanic activity belched noxious elements into the atmosphere. This atmosphere, too, resembles nothing we see today. There was plenty of water vapor the stuff that clouds are made of, but the air was mostly carbon dioxide and hydrogen. This period in Earth&rsquos history is known as the Hadean Eon after Hades, the Greek god of the Underworld. It is an appropriate name there are no signs of life.

Artist's concept of early Earth

Earth is Like an Ogre, It has Layers

The lack of life does not mean that nothing is moving, growing, or changing. The interior of the newly formed Earth is hot and molten, allowing elements and magic to move freely within the planet. Heavier elements, mostly iron with some nickel, are pulled into the center of the planet by gravity in a process called differentiation lighter elements like carbon and oxygen remain closer to the surface. The high pressure at the center of the Earth means that even though the iron core is hot enough to be a liquid, it is compressed into a solid instead. This solid mass is the innermost layer of the Earth, known as the inner core.

The second layer is also made up of the same heavy elements. In fact, about a third of Earth&rsquos mass and all but one percent of the total iron in the planet are contained within the first two layers. However, the outer core, this second layer, is not subjected to the same pressure as the inner core so this layer is liquid, rather than solid. Many believe that the innermost layers contain vast amounts of untapped magical energy, though no one has been able to create an instrument that can survive long enough to prove this.

The largest layer by far is the mantle. This third layer makes up more than eighty percent of the planet and contains about half its mass. This layer is generally a solid, however over very long periods of time it can be seen to move and change. This is also the only interior layer that we can ever see. Material from this layer is the molten rock that comes to the surface around volcanos. While the rocky material in this layer moves incredibly slowly, energy is still able to move through it bringing heat and magic from the core closer to the surface of the Earth. In places where the surface layer of the Earth is thinner, people have begun to harvest this heat as geothermal energy. High volcanic activity is also the cause of greater concentrations of more &ldquowild&rdquo magic. Here there is a greater concentration of raw power coming from the center of the earth, as opposed to the magic from the sun which is filtered by the atmosphere.

The final, fourth, layer of the Earth is smallest, but also the most important from a human perspective. The thin shell of the planet is the crust. Here is where we live, work, and play, and also what keeps the hot inner layers from instantly vaporizing the seas. There are cracks, places where the mantle can come through, but the crust protects us all from the other hotter and more unpredictable layers. It is not one solid piece but rather many pieces interacting with each other and floating on the mantle beneath them.

The map of Earth we know today is far different from the Earth that came into being so many millions of years ago. In fact, the continental plates that exist today are far younger than Earth itself, owing to tectonic movement, the motion of crust plates floating on the mantle meteor impacts and extreme volcanic activity that characterized the early Earth. Supercontinents, the term used to refer to early, massive continental structures, have come and gone throughout the history of Earth. Our current continents are fragments of the most recent supercontinent: Pangea.

One of the first supercontinents known to exist on Earth is called Vaalbara, named for the men who discovered evidence of its existence. While most of Vaalbara has been completely destroyed by geological processes, evidence has been found in Africa and Australia. Cratons, stable pieces of continents, discovered at sites on both modern continents, date back to about three and a half billion years ago. Fossils discovered here have revealed some of the earliest known fossils as well as evidence of photosynthesis, the process by which plants produce oxygen.

Kenorland is another supercontinent that formed about 2.7 billion years ago. This continent is thought to have formed by accretion, similar to the formation of the Earth, except that in this case cratons came together on Earth&rsquos surface to create a very large land mass. Intense volcanic activity across this continent caused it to break up.

Several other supercontinents came together and fell apart over the millennia including Columbia, Rodinia, and Pannotia. Some of these lasted longer than others. However, many of these continents were made up of cratons that form the basis of continents today. Parts of Africa, Antarctica, and Russia have existed for far longer than the continents of which they are a part.

Scientific reconstruction of Rodinia Source

Siberia, an ancient craton located in the Russian heartland today, is actually about two and a half billion years old. For some time it was a continent alone, though it also became part of several other continents through accretion. It formed a major part of the supercontinent Rodinia, a name that comes from the Russian родина (&ldquorodina&rdquo) which means Motherland. Siberia also became an integral part of the most recent supercontinent, Pangea. Though it is mainly tundra and forest, today, geologists predict that another 250 million years from now Siberia may have a subtropical climate and be part of a new supercontinent altogether.

Scientific reconstruction of Pangea's continental drift Source

Pangea is the youngest supercontinent. It formed only about three hundred million years ago, but is also the first supercontinent to be reconstructed because of its relative youth. Pangea was made up of all the continental plates on Earth today, though it was located mainly in the Southern Hemisphere or the southern half of the planet. The name comes from the Greek word pan meaning whole and the Greek word for Mother Earth, Gaia . Approximately 175 million years ago Pangea began to break up. Continental drift and volcanic activity pushed the various tectonic plates apart. Over millions of years the continents moved into place as we know them today. However, these plates are still moving and the face of our Earth is changing because of them.

Shake and Bake

The plates that make up the Earth&rsquos crust are constantly moving, growing, and shrinking. Heat from the core makes them drift apart and clash together, and in doing so they have shaped the world we live in this is plate tectonics.

There are two types of plates: continental which are thick, less dense plates that have continents on them and oceanic which are thinner, denser plates located under the oceans. Boundaries form where plates interact with each other. These come in three types: converging, diverging, and transform.

Converging boundaries come in three types that create their own physical features. When two oceanic plates come together, the older, denser plate goes through subduction &ndash the plate is forced down and into the mantle beneath the less dense plate. As the subducting plate begins to melt, molten rock known as magma begins to rise. Where this magma is forced to the surface, volcanos form. Subduction also occurs when an oceanic plate and a continental plate converge. The continental plate forces the dense oceanic plate downwards. This type of plate boundary is seen best in the Ring of Fire, the boundary of the Pacific Plate which created a large number of volcanos. Finally, when two continental plates converge they push up against each other, causing the plate material to fold up into ridges, creating mountains.

Map of the Ring of Fire Source

Diagram of converging boundaries Source

Diverging boundaries are where plates are moving away from each other. Heat from the mantle below pushes upwards, pushing the plates apart. Molten rock from beneath the plates is forced up into the gap, where it cools and becomes part of the new plate boundary. When continental plates diverge they create large rift valleys and are often filled with water making long, skinny lakes. When oceanic plates diverge magma is cooled more rapidly by the water, forming a large ridge of new rock like the Mid-Atlantic Ridge, which also resulted in the formation of Iceland, a relatively small island with a lot of volcanic activity.


Finally, transform boundaries occur when plates are moving up against and past each other. Since tectonic plates rarely have smooth edges, they do not slide easily. Sometimes they get locked together which stores up a tremendous amount of energy. Heat and pressure within locked up plates also cause a buildup of magical energy stored within the crust from the Earth&rsquos formation. Once energy builds up past the resistance of the rock, the plates release suddenly, sliding past each other, creating shockwaves called earthquakes.

Diagram of a transform boundary Source

Earthquakes generate seismic waves, waves of energy and magic that travel through the Earth&rsquos crust from the point at which the earthquake was generated, the epicenter, outwards to the surrounding area like ripples in a pond. This can cause massive amounts of damage to buildings, roads, and other infrastructure located on top of the shaking ground. There are several scales for measuring the strength of earthquakes but the most common is the Richter magnitude scale. Created in 1979 by the Muggle physicist and seismologist Charles Francis Richter, this scale is used to demonstrate the strength of an earthquake. This scale is measured in factors of ten: this means that an earthquake that measures 7 on the Richter scale is ten times as powerful as an earthquake that is measured at a 6 on the Richter scale.

The release of magical energy during an earthquake can also have very damaging effects on nearby objects and enchantments. The rippling shockwaves of magic can disrupt nearby spells and charms, causing them to fail or backfire. In 1938, Hubert Keiser, a magical physicist and inventor in Los Angeles, California, noticed that enchanted clocks often stopped during earthquakes, a common occurrence in that area. When the shaking was more noticeable, the clocks were behind for a longer amount of time. Keiser then set many magical clocks throughout the city in an attempt to measure the strength of the disturbance, which led to the development of the Keiser disturbance magnitude scale. The Keiser scale measures magical disturbance in factors of seven. An earthquake that is a 5 on the Keiser scale is seven times more powerful than one that is only a 4 on the Keiser scale.

The cracked lunascope you see before me was sent to me by a friend from my time at Durmstrang. He now lives in Christchurch, New Zealand, which suffered an earthquake in 2011 measured at 6.3 on the Richter scale and at 7.5 on the Keiser scale. As you can see it has been broken beyond use or repair as a result of the magical shockwave that went through the city, as well as the rather heavy bookcase that fell on top of it.

Christchurch Earthquake: February 22, 2011 Source

That will be all for this week. Do remember to look over your notes before our next class, as you will also be taking your midterms next week. In addition to the information we have already covered, we will also be looking at the various ways that we are protected from interstellar dangers by the Earth.

Our Big Blue Marble - Earth is the only planet we call home it is what gives us life and security even as we look to the heavens all around us. In order to study the heavens, however, it is first necessary to understand ourselves. What makes the Earth so special and why are we the only planet in our whole Solar System known to contain life? This year is intended to give Astronomy students a foundation in our Earth even as we seek to compare ourselves to others. Students will leave this class with a better understanding of their own place in the universe, the ability to compare Earth with other planets, knowledge of the origins of magic in our near universe, and an appreciation for the uniqueness of the planet we call home.

LPI | Education

What is volcanism?
Volcanism is the eruption of molten rock (magma) onto the surface of a planet. A volcano is the vent through which magma and gases are discharged. Magma that reaches the surface is called “lava.” Volcanos are named for Vulcan — the Roman god of fire!

Why and where do volcanos form?
Volcanism is the result of a planet losing its internal heat. Volcanos can form where rock near the surface becomes hot enough to melt. On Earth, this often happens in association with plate boundaries (check out the section on tectonism). Where two plates move apart, such as at mid-ocean volcanic ridges, material from Earth's interior slowly rises up, melts when it reaches lower pressures, and fills in the gap. Where one plate is being subducted under another, chambers of magma may form. These magma bodies feed the volcanic islands that mark subduction zones.

Although most volcanic activity takes place at plate boundaries, volcanism also can occur within the plate interiors at hotspots. Hotspots are thought to be from large “plumes” of extremely hot material rising from deep in Earth's interior. The hot material rises slowly, eventually melting as it reaches lower pressures near Earth's surface. When the material erupts it forms massive lava flows of fine-grained dark volcanic rock — basalt. The broad, gentle shield volcanos of Hawai'i come from a hotspot.

What do Earth's volcanos tell us?
The fact that Earth has volcanos tells us that Earth's interior is circulating and is hot — hot enough to melt. Earth is cooling volcanos are one way to lose heat. The pattern of distribution of volcanos on Earth gives us a clue that Earth's outer surface is divided into plates the chains of volcanos associated with mid-ocean ridges and subduction zones mark the plate edges. Other planets have volcanic features — some recently active — telling geologists that they, too, are losing heat from their interiors and that there is circulation. However, these planets do not display the pattern that Earth's volcanos do.

What evidence is there of volcanism on other planets?
Moon: Our closest neighbor has small volcanos, fissures (breaks in the crust), and extensive flows of basalt, a fine-grained dark volcanic rock. The large dark basins that you can see on the Moon are the maria — areas of these lava flows. However, all these volcanic features are old. There are no active volcanic features on the Moon. Most of the volcanic activity took place early in the Moon's history, before about 3 billion years ago. The most recent lava flow occurred about 1 billion years ago.

Dark regions on the Moon are lunar maria. These are low, smooth regions of dark, fine-grained volcanic rock — basalt.

Galileo spacecraft image (PIA00405) produced by the U.S. Geological Survey, courtesy of NASA and the Jet Propulsion Laboratory.

This rock sample was collected by the Apollo 15 mission in 1971. It is a basalt, a type of rock that solidifies from a volcanic lava. This particular basalt formed 3.3 billion years ago and is similar to basalts formed at volcanos such as Hawai'i on Earth.

Mars: Mars has volcanic features that are similar in shape to those on Earth, although much larger. There are large shield volcanos — like those in Hawai'i — that contain 100 times more mass that those on Earth. Olympus Mons is the tallest volcano in our solar system. It is 22 kilometers (14 miles) tall, compared to Mauna Loa's 9 kilometers (almost 6 miles). It is 600 kilometers across (375 miles), which is large enough to cover the state of Arizona! Several of the volcanos on Mars, including Olympus Mons, occur in the Tharsis region the magma for the volcanos may come from hot material welling up in plumes from deep in Mars' interior. Many scientists consider Mars to be volcanically active, even if we have not observed an eruption. Basalt meteorites from Mars indicate that volcanism has occurred in the last 180 million years. Very few impact craters occur on the lava flows of Olympus Mons, suggesting that this volcano has probably erupted in the last few million years.

Oblique view of the Olympus Mons volcano on Mars. The large depression in the upper center of the image is the caldera. The caldera is located near the summit of the volcano and is 65 × 80 kilometers (40 × 50 miles) across — about the size of Rhode Island. When magma erupted out of vents on the side of the volcano, the rock near the summit collapsed, producing the caldera.

Viking Orbiter image (641A52) courtesy of NASA.

Venus: Venus has more than 1700 volcanic features and many of these look fresh — unweathered. Much of the surface of Venus has been covered by huge flows of basalt lava, probably in the last few hundred million years. This blanket of lava completely covered the surface features, such as impact craters. The fact that only a few craters dot the surface provides evidence of the recent nature of this resurfacing.

Computer-generated view of Maat Mons on Venus. This image is from Magellan spacecraft radar data the atmosphere of Venus is too thick for telescopes to see through. Dark areas are smooth, interpreted to be older lava flows. Bright areas are rough, interpreted to be young lava flows.

Image courtesy of NASA and the Jet Propulsion Laboratory.

Io: Jupiter's innermost moon, Io, is the most volcanically active body in our entire solar system! NASA missions imaged massive plumes shooting hundreds of kilometers above the surface, active lava flows, and walls of fire associated with magma flowing from fissures. The entire surface of Io is covered with volcanic centers and lava flows, which have covered all of its impact craters.

Voyager image of Io. The dark spots mark volcanos.

Image courtesy of NASA and the Jet Propulsion Laboratory.

The Galileo spacecraft captured this image of an active volcanic eruption on Io in 2000. The bright orange region is hot lava. This false-color picture is about 250 kilometers (about 155 miles) across.

Image produced by the University of Arizona, courtesy of NASA.

Why don't we find active volcanos on all planets and moons?
Active volcanos occur on planets that are still hot. In general, the larger the planet, the slower it cools. Small planets or moons, like Mercury and our Moon, have cooled to the point that they are no longer hot enough to melt rock. Larger planets, like Earth and Venus, are still hot and still have active volcanism.

Mars is the fourth planet from the sun in our solar system and even though it resembles Earth so much, it is only about half its size. The surface of mars is.

Fusion is when two atomic nuclei combine to form a heavier nucleus which results in the release of many photons. The photons released are the light that we s.

The lithosphere is very rigid it does not flow like the asthenosphere. The crust itself, which is contained in the lithosphere, can also be divided into two.

Lesson 1: Earthquakes and Volcanoes Layers of the Earth Earth is made up of three layers: crust, mantle and core. The outer layer is the crust, the midd.

Further evidence was Deccan volcanic rock has been found near the KT boundary, the chemical breakdown shows they were found in the Earth's mantle, an area ri.

Introduction Adakites are volcanic rocks that are diagnostic of high temperature, high pressure conditions, (Stevenson, 2005). Their composition ranges fr.

In this scenario, the period, or length to complete a cycle is 687 days (on Earth). This is because 687 days is the time that Mars takes to complete a single.

However, the heat energy was much greater in the early stages of the Earth because the heat is constantly created and lost from the interior of the earth. Th.

It’s composed of volcanic lava and sediments forming andesite and granite. 2. Oceanic Crust. It is the crust that lies beneath the oceans’ bed and is thin. T.

Many believe that Mercury is the hottest planet in the solar system since it is the planet closest to the sun. However, Venus is the hottest planet in the so.

Crust thick enough to prevent volcanos - Astronomy

The Earth's lithosphere is broken up into chunks called plates with densities around 3. Oceanic plates are made of basalts (cooled volcanic rock made of silicon, oxygen, iron, aluminum, & magnesium). Oceanic crust is only about 6 kilometers thick. The continental plates are made of another volcanic type of silicates called granite. Continental crust is much thicker than oceanic crust---up to 35 kilometers thick. With densities of 2.7 to 2.8 (times that of water), continental plates are less dense than the oceanic plates which have densities of 3. The mantle convection causes the crustal plates to slide next to or under each other, collide against each other, or separate from one another in a process called plate tectonics. Plate tectonics is the scientific theory that describes this process and how it explains the Earth's surface geology. The Earth is the only planet among the terrestrial planets that has this tectonic activity. This is because plate tectonics probably requires liquid water to solidify the oceanic plates at the mid-ocean ridges where seafloor spreading is happening (see below) and more importantly, the liquid water lubricates the asthenosphere and softens the lithosphere enough so that the plates can slide past or under one another. Venus has enough interior heat to have convection in its mantle like the Earth, but through processes described in another section, Venus lost its water, so its plates are poorly lubricated at best.

Plate Tectonics Theory Evidence

  • Continental motion: The locations of rock-types and certain fossil plants and animals on present-day, widely separated continents would form definite patterns if the continents were once joined. For example the eastern side of South America fits nicely next to the western edge of Africa and several fossil areas match up nicely at those points of intersection.
  • Seafloor spreading: An immense submarine mountain chain zig-zags between the continents and winds its way around the globe. At or near the crest of the ridge, the rocks are very young, and become progressively older away from the ridge crest. The youngest rocks at the ridge crest always have present-day (normal) magnetic polarity. Stripes of rock parallel to the ridge crest alternate in magnetic polarity (normal-reversed-normal, etc.)

Alternating stripes of magnetically different rock are laid out in rows on either side of the mid-ocean ridges: one stripe with normal polarity and the adjoining stripe with reversed polarity. This happens when magnetite in molten rock at the ridge aligns itself with the Earth's magnetic field. When the molten rock with the magnetite hardens, it "freezes" in the orientation of the Earth's magnetic field at that time. The Earth's magnetic field has changed polarity numerous times in its history with a 300,000 year average time interval between reversals (some reversals were just tens of thousands of years apart and others millions of years apart). When the Earth's magnetic field changes polarity, newly rising molten rock at the ridges will have its magnetite aligned accordingly. New oceanic crust is forming continuously at the crest of the mid-ocean ridge and cools to become solid crust. The oceanic crust becomes increasingly older at increasing distance from the ridge crest with seafloor spreading. The result will be a zebra-like striping of the magnetic polarity in the rock that parallels the mid-ocean ridge. Further evidence for seafloor spreading comes from determining ages of the seafloor at various distances from the mid-ocean ridges.

Plate Tectonics Process

The figure below shows the boundaries of the major plates on top of a map of the Earth. The arrows show the direction of the plates with respect to each other. The white areas are elevations greater than 2400 meters (7900 feet) above sea level. This figure is an adaption of a map in the "Plate Tectonic Movement Visualizations" website of the Science Education Resource Center at Carleton College and the plate motion data from This Dynamic Earth of the USGS. Select the figure to bring up an enlarged version of it.

Places where warm rock from the asthenosphere rises along weak points in the lithosphere can push apart the lithosphere on both sides (see the figure below). These places are at the mid-ocean ridges (such as the Mid-Atlantic Ridge that bisects the Atlantic Ocean) and continental rift zones (such as the East Africa Rift Zone). Sea-floor spreading caused the Atlantic Ocean to grow from a thin sliver 100 to 200 million years ago to its present size and now continues at a rate of about 25 kilometers per million years.

This pushing apart of some plates from each other means that others will collide. The oceanic lithosphere is cooled by contact with the ocean water. When oceanic crust runs into oceanic crust or into continental crust, the denser lithosphere material slides under the less dense lithosphere material, eventually melting in the deepest layers of the mantle. The region where the lithosphere pieces contact each other is called a subduction zone and a trench is formed there. At the subduction zone, the right combination of temperature, pressure and rock composition can create small pockets or fissures of molten rock in the solid asthenosphere that then rise up through cracks in the crust to create a range of volcanoes (see the figure below). In another section you will see that this has a profound effect on regulating the climate of the Earth.

When two continental pieces bump into each other, they are too light relative to the asthenosphere and too thick for one to be forced under the other. The plates are pushed together and buckle to form a mountain range. It also possible for two plates to slide past each other at what is called a transform fault such as the San Andreas Fault in California and the Anatolian Fault in Turkey.

Examples of ocean-continental plate subduction include the Juan de Fuca plate off the coast of northwestern United States subducting under the North American continental plate to create the Cascade volcano range, the Nazca plate subducting under the western edge of the South American plate to create the Andes range of volcanic mountains. An example of the ocean-ocean plate subduction are the chains of islands on the Asia side of the Pacific: the Aleutians, Japan, Philippines, Indonesia, and Marianas. An example of continent-continent plate collision is the Indian plate running into the Eurasian plate to create the Himalayas.

A lot of information and videos about Earth's plate tectonics are available on the EarthScope website. Students and teachers should also check out the IRIS Earth Science animations website for many high-quality and detailed animations of the plate tectonic activity occuring around the globe.


To end the Planet Interiors section, here is a summary of the terrestrial planet surface shaping agents at work today.

Surface Shaper Agent Mercury Venus Earth Moon Mars
Impact Cratering Yes Minor Minor Yes Yes
Volcanism (needs internal heat) No (only long ago) Yes Yes No (only long ago) No (only in the past)
Tectonics (needs internal heat) No (only long ago) Yes Yes No No (only in the past)
Erosion No (no liquid or atmosphere) No (no surface winds) Yes (ice, water, air) No (no liquid or atmosphere) Yes (air today + water in past)

Looking at the table, we can draw some conclusions as to what planet properties will determine the type of planet surfacing that can occur. Impact cratering can occur on any object with a solid surface at any time. If a planet has an atmosphere and is still geologically active, then the effects of impact cratering will be erased. Volcanism and Tectonics require the planet to be of sufficient size to still have heat in its interior. Erosion requires an atmosphere with winds to work efficiently. Even better is if liquid can be present to add to the weathering by the atmosphere. Erosion works best on Earth. Earth is of sufficient size to hang on to its atmosphere (unlike the Moon). Earth is at a good distance from the Sun so it is not too hot for its atmosphere to either evaporate away or become excessively thick that winds will not blow on the surface (as is the situation with Venus). Also, its good distance from the Sun enables the surface temperatures to be warm enough for liquid water to flow (unlike Mars) and so its atmosphere does not freeze out on its surface as happens with Mars. Earth's rotation is fast for its size (unlike Venus), so it can create complicated air circulation (wind) patterns as well as ocean currents. Also, rapid rotation enables the creation of the magnetic field shield to protect a planet's atmosphere from the solar wind.


Review Questions

  1. Why are almost all impact craters round?
  2. How can you use the number of craters to determine the age of a planet's or moon's surface?
  3. The lunar highlands have about ten times more craters on a given area than do the maria. Does this mean that the highlands are ten times older? Explain your reasoning.
  4. What determines if volcanism will make a steep-sided mountain or something with a gentler slope?
  5. How do shield volcanoes compare in size to stratovolcanoes in diameter and height?
  6. How do volcanic eruptions affect a planet's atmosphere?
  7. What does volcanism require as far as interior conditions?
  8. How does erosion change the surface of a planet (or moon)?
  9. What is the difference of a valley carved by glaciers vs. one carved by flowing water?
  10. Besides wearing away geological features, what does the process of erosion do?
  11. How is tectonics different than plate tectonics?
  12. What does tectonics require as far as interior conditions?
  13. How does the plate tectonics theory explain such things as the widening of the Atlantic Ocean, the Andes of South America and the Cascades of the northwestern U.S, and the high mountain ranges such as the Himalayas and the Rocky Mountains?
  14. What is the evidence for plate tectonics?
  15. What properties of a planet will determine what type of planet shaping can occur on it?
  16. What type of planet shaping occurs on Mercury, on Venus, on Mars, and on the Earth and the Moon?

NASA wants to prevent the Yellowstone super volcano from destroying the US

NASA believes the Yellowstone super volcano is a greater threat to life on Earth than any asteroid. So it’s come up with a plan to defuse its explosive potential.

Yellowstone National Park is the pride of the United States. It's an untouched wilderness. It’s overflowing with scenic landscapes. And its colourful hot pools and geysers attract tens of thousands of visitors every year.

But underneath this beautiful — but thin — skin is a lurking monster. An enormous pool of magma sits high in the Earth’s crust.

“I was a member of the NASA Advisory Council on Planetary Defense which studied ways for NASA to defend the planet from asteroids and comets,” Brian Wilcox of NASA’s Jet Propulsion Laboratory (JPL) told the BBC. “I came to the conclusion during that study that the super volcano threat is substantially greater than the asteroid or comet threat.”

There are about 20 known super volcanoes on Earth, NASA says. A major eruption occurs about once every 100,000 years. And these odds are much higher than a repeat of an Earth-changing comet impact of the type that wiped out the dinosaurs.

So NASA tasked a team with figuring out how to prevent one.

A super volcano is very different from the common conception of tall cones of rock and ash that occasionally catastrophically erupt.

Instead, it’s a vast space of collapsed crust that can cover hundreds of square kilometers.

Instead, vast quantities of searing magma and clouds of fumes would slowly crawl across the landscape — burying much of the United States under a thick coat of ash and lava.

In the case of Yellowstone, it’s enough to change the climate of the world for several centuries.

An event in Indonesia, about 75,000 years ago, named the Toba catastrophe, pumped some 4000 tons of hydrogen sulphide gas into the atmosphere along with about 2800 cubic kilometres of ejecta. This produced a global volcanic winter that lasted a decade.

Yellowstone isn’t expected to erupt any time soon. It appears to burst roughly once every 700,000 years. The most recent was 640,000 years ago, with other events 1.3 million years ago and 2.1 million years ago.

This is much more regular than cataclysmic comet impacts.

“When people first considered the idea of defending the Earth from an asteroid impact, they reacted in a similar way to the super volcano threat,” Wilcox said. “People thought, ‘As puny as we are, how can humans possibly prevent an asteroid from hitting the Earth’.”

NASA’s researchers have told the BBC they have explored what it would take to avert a super volcano catastrophe.

The answer: find a way to cool the magma down.

Supervolcanos only spill over when the molten rock is hot enough to become highly fluid.

In a slightly cooler state, it gets thicker. Stickier.

It’s not going anywhere fast.

To achieve this, the Jet Propulsion Labs team calculated a super volcano on the brink of eruption would have to be cooled some 35 per cent.

They propose to do this by pricking the supervolcano’s surface, to let off steam.

But this in itself poses risks.

Drill too deep, and the vent could cause an explosive depressurization that may set off the exact kind of eruption the scientists were trying to avoid.

Instead, the NASA scientists propose, a 10km deep hole into the hydrothermal water below and to the sides of the magma chamber. These fluids, which form Yellowstone’s famous heat pools and geysers, already drain some 60-70 per cent of the heat from the magma chamber below.

NASA proposes that, in an emergency, this enormous body of heated water can be injected with cooler water, extracting yet more heat.

This could prevent the super volcano’s magma from reaching the temperature at which it would erupt.

Such a project could cost in excess of $3.5 billion. But it’s nothing like the reconstruction cost of digging two thirds of the continental United States out from under mountains of volcanic ash.

And it could even help pay for itself.

Steam from the superheated water could be used to drive power turbines.

“You would pay back your initial investment, and get electricity which can power the surrounding area for a period of potentially tens of thousands of years,” NASA’s Brian Wilcox says.

Crust thick enough to prevent volcanos - Astronomy

When Mount Pinatubo suddenly erupted on 9 June 1991, the power of volcanoes past and present again hit the headlines

Volcanoes are the ultimate earth-moving machinery. A violent eruption can blow the top few kilometres off a mountain, scatter fine ash practically all over the globe and hurl rock fragments into the stratosphere to darken the skies a continent away.

But the classic eruption - cone-shaped mountain, big bang, mushroom cloud and surges of molten lava - is only a tiny part of a global story. Vulcanism, the name given to volcanic processes, really has shaped the world. Eruptions have rifted continents, raised mountain chains, constructed islands and shaped the topography of the earth. The entire ocean floor has a basement of volcanic basalt.

Volcanoes have not only made the continents, they are also thought to have made the world's first stable atmosphere and provided all the water for the oceans, rivers and ice-caps. There are now about 600 active volcanoes. Every year they add two or three cubic kilometres of rock to the continents. Imagine a similar number of volcanoes smoking away for the last 3,500 million years. That is enough rock to explain the continental crust.

What comes out of volcanic craters is mostly gas. More than 90% of this gas is water vapour from the deep earth: enough to explain, over 3,500 million years, the water in the oceans. The rest of the gas is nitrogen, carbon dioxide, sulphur dioxide, methane, ammonia and hydrogen. The quantity of these gases, again multiplied over 3,500 million years, is enough to explain the mass of the world's atmosphere. We are alive because volcanoes provided the soil, air and water we need.

Geologists consider the earth as having a molten core, surrounded by a semi-molten mantle and a brittle, outer skin. It helps to think of a soft-boiled egg with a runny yolk, a firm but squishy white and a hard shell. If the shell is even slightly cracked during boiling, the white material bubbles out and sets like a tiny mountain chain over the crack - like an archipelago of volcanic islands such as the Hawaiian Islands. But the earth is so much bigger and the mantle below is so much hotter.

Even though the mantle rocks are kept solid by overlying pressure, they can still slowly 'flow' like thick treacle. The flow, thought to be in the form of convection currents, is powerful enough to fracture the 'eggshell' of the crust into plates, and keep them bumping and grinding against each other, or even overlapping, at the rate of a few centimetres a year. These fracture zones, where the collisions occur, are where earthquakes happen. And, very often, volcanoes.

These zones are lines of weakness, or hot spots. Every eruption is different, but put at its simplest, where there are weaknesses, rocks deep in the mantle, heated to 1,350°C, will start to expand and rise. As they do so, the pressure drops, and they expand and become liquid and rise more swiftly.

Sometimes it is slow: vast bubbles of magma - molten rock from the mantle - inch towards the surface, cooling slowly, to snow through as granite extrusions (as on Skye, or the Great Whin Sill, the lava dyke squeezed out like toothpaste that carries part of Hadrian's Wall in northern England). Sometimes - as in Northern Ireland, Wales and the Karoo in South Africa - the magma rose faster, and then flowed out horizontally on to the surface in vast thick sheets. In the Deccan plateau in western India, there are more than two million cubic kilometres of lava, some of it 2,400 metres thick, formed over 500,000 years of slurping eruption.

Sometimes the magma moves very swiftly indeed. It does not have time to cool as it surges upwards. The gases trapped inside the boiling rock expand suddenly, the lava glows with heat, it begins to froth, and it explodes with tremendous force. Then the slightly cooler lava following it begins to flow over the lip of the crater. It happens on Mars, it happened on the moon, it even happens on some of the moons of Jupiter and Uranus. By studying the evidence, vulcanologists can read the force of the great blasts of the past. Is the pumice light and full of holes? The explosion was tremendous. Are the rocks heavy, with huge crystalline basalt shapes, like the Giant's Causeway in Northern Ireland? It was a slow, gentle eruption.

The biggest eruptions are deep on the mid-ocean floor, where new lava is forcing the continents apart and widening the Atlantic by perhaps five centimetres a year. Look at maps of volcanoes, earthquakes and island chains like the Philippines and Japan, and you can see the rough outlines of what are called tectonic plates - the plates which make up the earth's crust and mantle. The most dramatic of these is the Pacific 'ring of fire' where there have been the most violent explosions - Mount Pinatubo near Manila, Mount St Helen's in the Rockies and El Chichon in Mexico about a decade ago, not to mention world-shaking blasts like Krakatoa in the Sunda Straits in 1883.

But volcanoes are not very predictable. That is because geological time is not like human time. During quiet periods, volcanoes cap themselves with their own lava by forming a powerful cone from the molten rocks slopping over the rim of the crater later the lava cools slowly into a huge, hard, stable plug which blocks any further eruption until the pressure below becomes irresistible. In the case of Mount Pinatubo, this took 600 years.


It's a cloud-swaddled planet named for a love goddess, often called Earth&rsquos twin. But pull up a bit closer, and Venus turns hellish. Our nearest planetary neighbor, the second planet from the Sun, has a surface hot enough to melt lead. The atmosphere is so thick that, from the surface, the Sun is just a smear of light.

In some ways it is more an opposite of Earth than a twin: Venus spins backward, has a day longer than its year, and lacks any semblance of seasons. It might once have been a habitable ocean world, like Earth, but that was at least a billion years ago. A runaway greenhouse effect turned all surface water into vapor, which then leaked slowly into space. The present-day surface of volcanic rock is blasted by high temperatures and pressures. Asked if the surface of Venus is likely to be life-bearing today, we can give a quick answer: a hard &ldquono.&rdquo

Further, Venus may hold lessons about what it takes for life to get its start ­&ndash on Earth, in our solar system, or across the galaxy. The ingredients are all there, or at least, they used to be. By studying why our neighbor world went in such a different direction with regard to habitability, we could find out what could make other worlds right. And while it might sound absurd, we can&rsquot rule out life on Venus entirely. Temperature, air pressure, and chemistry are much more congenial up high, in those thick, yellow clouds.


The ancient Romans could easily see seven bright objects in the sky: the Sun, the Moon, and the five brightest planets (Mercury, Venus, Mars, Jupiter, and Saturn). They named the objects after their most important gods. Venus, the third brightest object after the Sun and Moon, was named after the Roman goddess of love and beauty. It&rsquos the only planet named after a female god.

Potential for Life

Thirty miles up (about 50 kilometers), temperatures range from 86 to 158 Fahrenheit (30 to 70 Celsius), a range that, even at its higher-end, could accommodate Earthly life, such as &ldquoextremophile&rdquo microbes. And atmospheric pressure at that height is similar to what we find on Earth&rsquos surface.

At the tops of Venus&rsquo clouds, whipped around the planet by winds measured as high as 224 miles (360 kilometers) per hour, we find another transformation. Persistent, dark streaks appear. Scientists are so far unable to explain why these streaks remain stubbornly intact, even amid hurricane-force winds. They also have the odd habit of absorbing ultraviolet radiation.

The most likely explanations focus on fine particles, ice crystals, or even a chemical compound called iron chloride. Although it's much less likely, another possibility considered by scientists who study astrobiology is that these streaks could be made up of microbial life, Venus-style. Astrobiologists note that ring-shaped linkages of sulfur atoms, known to exist in Venus&rsquo atmosphere, could provide microbes with a kind of coating that would protect them from sulfuric acid. These handy chemical cloaks would also absorb potentially damaging ultraviolet light and re-radiate it as visible light.

Some of the Russian Venera probes did, indeed, detect particles in Venus&rsquo lower atmosphere about a micron in length &ndash roughly the same size as a bacterium on Earth.

None of these findings provide compelling evidence for the existence of life in Venus&rsquo clouds. But the questions they raise, along with Venus&rsquo vanished ocean, its violently volcanic surface, and its hellish history, make a compelling case for a return to our temperamental sister planet. There is much, it would seem, that she can teach us.

Size and Distance

Our nearness to Venus is a matter of perspective. The planet is nearly as big around as Earth &ndash 7,521 miles (12,104 kilometers) across, versus 7,926 miles (12,756 kilometers) for Earth. From Earth, Venus is the brightest object in the night sky after our own Moon. The ancients, therefore, gave it great importance in their cultures, even thinking it was two objects: a morning star and an evening star. That&rsquos where the trick of perspective comes in.

Because Venus&rsquo orbit is closer to the Sun than ours, the two of them &ndash from our viewpoint &ndash never stray far from each other. The ancient Egyptians and Greeks saw Venus in two guises: first in one orbital position (seen in the morning), then another (your &ldquoevening&rdquo Venus), just at different times of the year.

At its nearest to Earth, Venus is some 38 million miles (about 61 million kilometers) distant. But most of the time the two planets are farther apart Mercury, the innermost planet, actually spends more time in Earth&rsquos proximity than Venus.

One more trick of perspective: how Venus looks through binoculars or a telescope. Keep watch over many months, and you&rsquoll notice that Venus has phases, just like our Moon &ndash full, half, quarter, etc. The complete cycle, however, new to full, takes 584 days, while our Moon takes just a month. And it was this perspective, the phases of Venus first observed by Galileo through his telescope, that provided the key scientific proof for the Copernican heliocentric nature of the Solar System.

Orbit and Rotation

Spending a day on Venus would be quite a disorienting experience &ndash that is, if your ship or suit could protect you from temperatures in the range of 900 degrees Fahrenheit (475 Celsius). For one thing, your &ldquoday&rdquo would be 243 Earth days long &ndash longer even than a Venus year (one trip around the Sun), which takes only 225 Earth days. For another, because of the planet's extremely slow rotation, sunrise to sunset would take 117 Earth days. And by the way, the Sun would rise in the west and set in the east, because Venus spins backward compared to Earth.

While you&rsquore waiting, don&rsquot expect any seasonal relief from the unrelenting temperatures. On Earth, with its spin axis tilted by about 23 degrees, we experience summer when our part of the planet (our hemisphere) receives the Sun&rsquos rays more directly &ndash a result of that tilt. In winter, the tilt means the rays are less direct. No such luck on Venus: Its very slight tilt is only three degrees, which is too little to produce noticeable seasons.




A critical question for scientists who search for life among the stars: How do habitable planets get their start? The close similarities of early Venus and Earth, and their very different fates, provide a kind of test case for scientists who study planet formation. Similar size, similar interior structure, both harboring oceans in their younger days. Yet one is now an inferno, while the other is the only known world &ndash so far &ndash to play host to abundant life. The factors that set these planets on almost opposite paths began, most likely, in the swirling disk of gas and dust from which they were born. Somehow, 4.6 billion years ago that disk around our Sun accreted, cooled, and settled into the planets we know today. Several might well have moved in closer, or farther out, as the solar system formed. Better knowledge of the formation history of Venus could help us better understand Earth&rsquos &ndash and those of rocky planets around other stars.


If we could slice Venus and Earth in half, pole to pole, and place them side by side, they would look remarkably similar. Each planet has an iron core enveloped by a hot-rock mantle the thinnest of skins forms a rocky, exterior crust. On both planets, this thin skin changes form and sometimes erupts into volcanoes in response to the ebb and flow of heat and pressure deep beneath.

Other possible similarities will require further investigation &ndash and perhaps another visit to a planet that has hosted many Earth probes, both in orbit and (briefly) on the surface. On Earth, the slow movement of continents over thousands and millions of years reshapes the surface, a process known as &ldquoplate tectonics.&rdquo Something similar might have happened on Venus early in its history. Today a key element of this process could be operating: subduction, or the sliding of one continental &ldquoplate&rdquo beneath another, which can also trigger volcanoes. Subduction is believed to be the first step in creating plate tectonics.

NASA&rsquos Magellan spacecraft, which ended a five-year mission to Venus in 1994, mapped the broiling surface using radar. Magellan saw a land of extreme volcanism. The orbiter saw a relatively young surface, one recently reshaped (in geologic terms), and chains of towering mountains.


The broiling surface of Venus has been a topic of heated discussion among planetary scientists. The traditional picture includes a catastrophic, planetwide resurfacing between 350 and 750 million years ago. In other words, Venus appears to have completely erased most traces of its early surface. The causes: volcanic and tectonic forces, which could include surface buckling and massive eruptions. But newer estimates made with help from computer models paint a different portrait. While the same forces would be at work, resurfacing would be piecemeal over an extended time. The average age of surface features could be as young as 150 million years, with some older surfaces mixed in.

Venus is a landscape of valleys and high mountains dotted with thousands of volcanoes. Its surface features &ndash most named for both real and mythical women &ndash include Ishtar Terra, a rocky, highland area around the size of Australia near the north pole, and an even larger, South-America-sized region called Aphrodite Terra that stretches across the equator. One mountain reaches 36,000 feet (11 kilometers), higher than Mt. Everest. Notably, except for Earth, Venus has by far the fewest impact craters of any rocky planet, revealing a young surface.

On your tour of Venus, during the 117 days you&rsquore waiting for sunset, you might stop by a volcanic crater, Sacajawea, named for Lewis and Clark&rsquos Native American guide. Or stroll through a deep canyon, Diana, named for the Roman goddess of the hunt.

Other notable features of the Venus landscape include:

&ldquoPancake&rdquo domes with flat tops and steep sides, as wide as 38 miles (62 kilometers), likely formed by the extrusion of highly viscous lava.

&ldquoTick&rdquo domes, odd volcanoes with radiating spurs that, from above, make them look like their blood-feeding namesake.

Tesserae, terrain with intricate patterns of ridges and grooves that suggest the scorching temperatures make rock behave in some ways more like peanut butter beneath a thin and strong chocolate layer on Venus.


The Soviet Union landed 10 probes on the surface of Venus, but even among the few that functioned after landing, the successes were short-lived &ndash the longest survivor lasted two hours the shortest, 23 minutes. Photos snapped before the landers fried show a barren, dim, and rocky landscape, and a sky that is likely some shade of sulfur yellow.

Venus&rsquo atmosphere is one of extremes. With the hottest surface in the solar system, apart from the Sun itself, Venus is hotter even than the innermost planet, charbroiled Mercury. To outlive the short-lived Venera probes, your rambling sojourn on Venus would presumably include unimaginably strong insulation as temperatures push toward 900 degrees Fahrenheit (482 Celsius). You would need an extremely thick, pressurized outer shell to avoid being crushed by the weight of the atmosphere &ndash which would press down on you as if you were 0.6 miles (1 kilometer) deep in the ocean.

The atmosphere is mostly carbon dioxide &ndash the same gas driving the greenhouse effect on Venus and Earth &ndash with clouds composed of sulfuric acid. And at the surface, the hot, high-pressure carbon dioxide behaves in a corrosive fashion. But a stranger transformation begins as you rise higher. Temperature and pressure begin to ease.


Even though Venus is similar in size to Earth and has a similar-sized iron core, the planet does not have its own internally generated magnetic field. Instead, Venus has what is known as an induced magnetic field. This weak magnetic field is created by the interaction of the Sun's magnetic field and the planet's outer atmosphere. Ultraviolet light from the Sun excites gases in Venus' outermost atmosphere these electrically excited gases are called ions, and thus this region is called the ionosphere (Earth has an ionosphere as well). The solar wind &ndash a million-mile-per-hour gale of electrically charged particles streaming continuously from the Sun &ndash carries with it the Sun's magnetic field. When the Sun's magnetic field interacts with the electrically excited ionosphere of Venus, it creates or induces, a magnetic field there. This induced magnetic field envelops the planet and is shaped like an extended teardrop, or the tail of a comet, as the solar wind blows past Venus and outward into the solar system.


The word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology. [1] The study of volcanoes is called volcanology, sometimes spelled vulcanology. [2]

According to the theory of plate tectonics, the Earth's lithosphere, its rigid outer shell, is broken into sixteen larger plates and several smaller plates. These are in slow motion, due to convection in the underlying ductile mantle, and most volcanic activity on Earth takes place along plate boundaries, where plates are converging (and lithosphere is being destroyed) or are diverging (and new lithosphere is being created.) [3]

Divergent plate boundaries

At the mid-oceanic ridges, two tectonic plates diverge from one another as hot mantle rock creeps upwards beneath the thinned oceanic crust. The decrease of pressure in the rising mantle rock leads to adiabatic expansion and the partial melting of the rock, causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, and so most volcanic activity on the Earth is submarine, forming new seafloor. Black smokers (also known as deep sea vents) are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea level, volcanic islands are formed, such as Iceland. [4]

Convergent plate boundaries

Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. The oceanic plate subducts (dives beneath the continental plate), forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, thus creating magma. This magma tends to be extremely viscous because of its high silica content, so it often does not reach the surface but cools and solidifies at depth. When it does reach the surface, however, a volcano is formed. Thus subduction zones are bordered by chains of volcanoes called volcanic arcs. Typical examples are the volcanoes in the Pacific Ring of Fire, such as the Cascade Volcanoes or the Japanese Archipelago, or the Sunda Arc of Indonesia. [5]


Hotspots are volcanic areas thought to be formed by mantle plumes, which are hypothesized to be columns of hot material rising from the core-mantle boundary. As with mid-ocean ridges, the rising mantle rock experiences decompression melting which generates large volumes of magma. Because tectonic plates move across mantle plumes, each volcano becomes inactive as it drifts off the plume, and new volcanoes are created where the plate advances over the plume. The Hawaiian Islands are thought to have been formed in such a manner, as has the Snake River Plain, with the Yellowstone Caldera being the part of the North American plate currently above the Yellowstone hotspot. [6] However, the mantle plume hypothesis has been questioned. [7]

Continental rifting

Sustained upwelling of hot mantle rock can develop under the interior of a continent and lead to rifting. Early stages of rifting are characterized by flood basalts and may progress to the point where a tectonic plate is completely split. [8] [9] A divergent plate boundary then develops between the two halves of the split plate. However, rifting often fails to completely split the continental lithosphere (such as in an aulacogen), and failed rifts are characterized by volcanoes that erupt unusual alkali lava or carbonatites. Examples include the volcanoes of the East African Rift. [10]

The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit however, this describes just one of the many types of volcano. The features of volcanoes are much more complicated and their structure and behavior depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have landscape features such as massive plateaus. Vents that issue volcanic material (including lava and ash) and gases (mainly steam and magmatic gases) can develop anywhere on the landform and may give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Hawaii's Kīlauea. Other types of volcano include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter, Saturn, and Neptune and mud volcanoes, which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes except when the mud volcano is actually a vent of an igneous volcano.

Fissure vents

Volcanic fissure vents are flat, linear fractures through which lava emerges.

Shield volcanoes

Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent. They generally do not explode catastrophically, but are characterized by relatively gentle effusive eruptions. Since low-viscosity magma is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland, as well.

Lava domes

Lava domes are built by slow eruptions of highly viscous lava. They are sometimes formed within the crater of a previous volcanic eruption, as in the case of Mount St. Helens, but can also form independently, as in the case of Lassen Peak. Like stratovolcanoes, they can produce violent, explosive eruptions, but the lava generally does not flow far from the originating vent.


Cryptodomes are formed when viscous lava is forced upward causing the surface to bulge. The 1980 eruption of Mount St. Helens was an example lava beneath the surface of the mountain created an upward bulge, which later collapsed down the north side of the mountain.

Cinder cones

Cinder cones result from eruptions of mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 meters (100 to 1,300 ft) high. Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico, Caja del Rio is a volcanic field of over 60 cinder cones.

Based on satellite images, it was suggested that cinder cones might occur on other terrestrial bodies in the Solar system too on the surface of Mars and the Moon. [11] [12] [13] [14]

Stratovolcanoes (composite volcanoes)

  1. Large magma chamber
  2. Bedrock
  3. Conduit (pipe)
  4. Base
  5. Sill
  6. Dike
  7. Layers of ash emitted by the volcano
  8. Flank
  9. Layers of lava emitted by the volcano
  10. Throat
  11. Parasitic cone
  12. Lava flow
  13. Vent
  14. Crater
  15. Ash cloud

Stratovolcanoes (composite volcanoes) are tall conical mountains composed of lava flows and tephra in alternate layers, the strata that gives rise to the name. Stratovolcanoes are also known as composite volcanoes because they are created from multiple structures during different kinds of eruptions. Classic examples include Mount Fuji in Japan, Mayon Volcano in the Philippines, and Mount Vesuvius and Stromboli in Italy.

Ash produced by the explosive eruption of stratovolcanoes has historically posed the greatest volcanic hazard to civilizations. The lavas of stratovolcanoes are higher in silica, and therefore much more viscous, than lavas from shield volcanoes. High-silica lavas also tend to contain more dissolved gas. The combination is deadly, promoting explosive eruptions that produce great quantities of ash, as well as pyroclastic surges like the one that destroyed the city of Saint-Pierre in Martinique in 1902. Stratovolcanoes are also steeper than shield volcanoes, with slopes of 30–35° compared to slopes of generally 5–10°, and their loose tephra are material for dangerous lahars. [15] Large pieces of tephra are called volcanic bombs. Big bombs can measure more than 4 feet(1.2 meters) across and weigh several tons. [16]


A supervolcano is a volcano that has experienced one or more eruptions that produced over 1,000 cubic kilometers (240 cu mi) of volcanic deposits in a single explosive event. [17] Such eruptions occur when a very large magma chamber full of gas-rich, silicic magma is emptied in a catastrophic caldera-forming eruption. Ash flow tuffs emplaced by such eruptions are the only volcanic product with volumes rivaling those of flood basalts. [18]

A supervolcano can produce devastation on a continental scale. Such volcanoes are able to severely cool global temperatures for many years after the eruption due to the huge volumes of sulfur and ash released into the atmosphere. They are the most dangerous type of volcano. Examples include Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico (both western United States) Lake Taupo in New Zealand Lake Toba in Sumatra, Indonesia and Ngorongoro Crater in Tanzania. Fortunately, supervolcano eruptions are very rare events, though because of the enormous area they cover, and subsequent concealment under vegetation and glacial deposits, supervolcanoes can be difficult to identify in the geologic record without careful geologic mapping. [19]

Submarine volcanoes

Submarine volcanoes are common features of the ocean floor. Volcanic activity during the Holocene Epoch has been documented at only 119 submarine volcanoes. but there may be more than one million geologically young submarine volcanoes on the ocean floor. [20] [21] In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above the ocean's surface. In the deep ocean basins, the tremendous weight of the water prevents the explosive release of steam and gases however, submarine eruptions can be detected by hydrophones and by the discoloration of water because of volcanic gases. Pillow lava is a common eruptive product of submarine volcanoes and is characterized by thick sequences of discontinuous pillow-shaped masses which form under water. Even large submarine eruptions may not disturb the ocean surface, due to the rapid cooling effect and increased buoyancy in water (as compared to air), which often causes volcanic vents to form steep pillars on the ocean floor. Hydrothermal vents are common near these volcanoes, and some support peculiar ecosystems based on chemotrophs feeding on dissolved minerals. Over time, the formations created by submarine volcanoes may become so large that they break the ocean surface as new islands or floating pumice rafts.

In May and June 2018, a multitude of seismic signals were detected by earthquake monitoring agencies all over the world. They took the form of unusual humming sounds, and some of the signals detected in November of that year had a duration of up to 20 minutes. An oceanographic research campaign in May 2019 showed that the previously mysterious humming noises were caused by the formation of a submarine volcano off the coast of Mayotte. [22]

Subglacial volcanoes

Subglacial volcanoes develop underneath icecaps. They are made up of lava plateaus capping extensive pillow lavas and palagonite. These volcanoes are also called table mountains, tuyas, [23] or (in Iceland) mobergs. [24] Very good examples of this type of volcano can be seen in Iceland and in British Columbia. The origin of the term comes from Tuya Butte, which is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analyzed and so its name has entered the geological literature for this kind of volcanic formation. [25] The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near the boundary with the Yukon Territory.

Mud volcanoes

Mud volcanoes (mud domes) are formations created by geo-excreted liquids and gases, although there are several processes which may cause such activity. [26] The largest structures are 10 kilometers in diameter and reach 700 meters high. [27]

The material that is expelled in a volcanic eruption can be classified into three types:

    , a mixture made mostly of steam, carbon dioxide, and a sulfur compound (either sulfur dioxide, SO2, or hydrogen sulfide, H2S, depending on the temperature) , the name of magma when it emerges and flows over the surface , particles of solid material of all shapes and sizes ejected and thrown through the air [28][29]

Volcanic gases

The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide [30] and sulfur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.

Lava flows


The form and style of eruption of a volcano is largely determined by the composition of the lava it erupts. The viscosity (how fluid the lava is) and the amount of dissolved gas are the most important characteristics of magma, and both are largely determined by the amount of silica in the magma. Magma rich in silica is much more viscous than silica-poor magma, and silica-rich magma also tends to contain more dissolved gases.

Lava can be broadly classified into four different compositions: [31]

    If the erupted magma contains a high percentage (>63%) of silica, the lava is described as felsic. Felsic lavas (dacites or rhyolites) are highly viscous and are erupted as domes or short, stubby flows. [32]Lassen Peak in California is an example of a volcano formed from felsic lava and is actually a large lava dome. [33]

Because felsic magmas are so viscous, they tend to trap volatiles (gases) that are present, which leads to explosive volcanism. Pyroclastic flows (ignimbrites) are highly hazardous products of such volcanoes, since they hug the volcano's slopes and travel far from their vents during large eruptions. Temperatures as high as 850 °C (1,560 °F) [34] are known to occur in pyroclastic flows, which will incinerate everything flammable in their path, and thick layers of hot pyroclastic flow deposits can be laid down, often many meters thick. [35] Alaska's Valley of Ten Thousand Smokes, formed by the eruption of Novarupta near Katmai in 1912, is an example of a thick pyroclastic flow or ignimbrite deposit. [36] Volcanic ash that is light enough to be erupted high into the Earth's atmosphere as an eruption column may travel hundreds of kilometers before it falls back to ground as a fallout tuff. Volcanic gases may remain in the stratosphere for years. [37]

Felsic magmas are formed within the crust, usually through melting of crust rock from the heat of underlying mafic magmas. The lighter felsic magma floats on the mafic magma without significant mixing. [38] Less commonly, felsic magmas are produced by extreme fractional crystallization of more mafic magmas. [39] This is a process in which mafic minerals crystallize out of the slowly cooling magma, which enriches the remaining liquid in silica.

Mafic lavas occur in a wide range of settings. These include mid-ocean ridges Shield volcanoes (such the Hawaiian Islands, including Mauna Loa and Kilauea), on both oceanic and continental crust and as continental flood basalts.

  • Some erupted magmas contain <=45% silica and produce ultramafic lava. Ultramafic flows, also known as komatiites, are very rare indeed, very few have been erupted at the Earth's surface since the Proterozoic, when the planet's heat flow was higher. They are (or were) the hottest lavas, and were probably more fluid than common mafic lavas, with a viscosity less than a tenth that of hot basalt magma. [44]

Lava texture

Mafic lava flows show two varieties of surface texture: ʻAʻa (pronounced [ˈʔaʔa] ) and pāhoehoe ( [paːˈho.eˈho.e] ), both Hawaiian words. ʻAʻa is characterized by a rough, clinkery surface and is the typical texture of cooler basalt lava flows. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Pāhoehoe flows are sometimes observed to transition to ʻaʻa flows as they move away from the vent, but never the reverse. [45]

More silicic lava flows take the form of block lava, where the flow is covered with angular, vesicle-poor blocks. Rhyolitic flows typically consist largely of obsidian. [46]


Tephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases. Magma commonly explodes as the gas dissolved in it comes out of solution as the pressure decreases when it flows to the surface. These violent explosions produce particles of material that can then fly from the volcano. Solid particles smaller than 2 mm in diameter (sand-sized or smaller) are called volcanic ash. [28] [29]

Tephra and other volcaniclastics (shattered volcanic material) make up more of the volume of many volcanoes than do lava flows. Volcaniclastics may have contributed as much as a third of all sedimentation in the geologic record. The production of large volumes of tephra is characteristic of explosive volcanism. [47]

Eruption styles are broadly divided into magmatic, phreatomagmatic, and phreatic eruptions. [48]

Magmatic eruptions

Magmatic eruptions are driven primarily by gas release due to decompression. [48] Low-viscosity magma with little dissolved gas produces relatively gentle effusive eruptions. High-viscosity magma with a high content of dissolved gas produces violent explosive eruptions. The range of observed eruption styles is expressed from historical examples.

Hawaiian eruptions are typical of volcanoes that erupt mafic lava with a relatively low gas content. These are almost entirely effusive, producing local fire fountains and highly fluid lava flows but relatively little tephra. They are named after the Hawaiian volcanoes.

Strombolian eruptions are characterized by moderate viscosities and dissolved gas levels. They are characterized by frequent but short-lived eruptions that can produce eruptive columns hundreds of meters high. Their primary product is scoria. They are named after Stromboli.

Vulcanian eruptions are characterized by yet higher viscosities and partial crystallization of magma, which is often intermediate in composition. Eruptions take the form of short-lived explosions over the course of several hours, which destroy a central dome and eject large lava blocks and bombs. This is followed by an effusive phase that rebuilds the central dome. Vulcanian eruptions are named after Vulcano.

Peléan eruptions are more violent still, being characterized by dome growth and collapse that produces various kinds of pyroclastic flows. They are named after Mount Pelée.

Plinian eruptions are the most violent of all volcanic eruptions. They are characterized by sustained huge eruption columns whose collapse produces catastrophic pyroclastic flows. They are named after Pliny the Younger, who chronicled the Plinian eruption of Mount Vesuvius in 79 AD.

The intensity of explosive volcanism is expressed using the Volcanic Explosivity Index (VEI), which ranges from 0 for Hawaiian-type eruptions to 8 for supervolcanic eruptions. [49]

Phreatomagmatic eruptions

Phreatomagmatic eruptions are characterized by interaction of rising magma with groundwater. They are driven by the resulting rapid buildup of pressure in the superheated groundwater.

Phreatic eruptions

Phreatic eruptions are characterized by superheating of groundwater that comes in contact with hot rock or magma. They are distinguished from phreatomagmatic eruptions because the erupted material is all country rock no new magma is erupted.

Volcanoes vary greatly in their level of activity, with individual volcanic systems having an eruption recurrence ranging from several times a year to once in tens of thousands of years. [50] Volcanoes are informally described as active, dormant, or extinct, but these terms are poorly defined. [51]


There is no consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By human lifespans, however, they are not.

Scientists usually consider a volcano to be erupting or likely to erupt if it is currently erupting, or showing signs of unrest such as unusual earthquake activity or significant new gas emissions. Most scientists consider a volcano active if it has erupted in the last 10,000 years (Holocene times)—the Smithsonian Global Volcanism Program uses this definition of active. As of March 2021 [update] , the Program recognizes 1,413 active volcanoes that have had eruptions during the Holocene Epoch. [52] Most volcanoes are situated on the Pacific Ring of Fire. [53] An estimated 500 million people live near active volcanoes. [53]

Historical time (or recorded history) is another timeframe for active. [54] [55] However, the span of recorded history differs from region to region. In China and the Mediterranean, it reaches back nearly 3,000 years, but in the Pacific Northwest of the United States and Canada, it reaches back less than 300 years, and in Hawaii and New Zealand, only around 200 years. [54] The incomplete Catalogue of the Active Volcanoes of the World, published in parts between 1951 and 1975 by the International Association of Volcanology, uses this definition, by which there are more than 500 active volcanoes. [54] [56] As of March 2021 [update] , the Smithsonian Global Volcanism Program recognizes 560 volcanoes with confirmed historical eruptions. [52]

As of 2013, the following are considered Earth's most active volcanoes: [57]

    , the famous Hawaiian volcano, was in nearly continuous, effusive eruption (in which lava steadily flows onto the ground) between 1983 through 2018, and had the longest-observedlava lake. and nearby Stromboli, two Mediterranean volcanoes in "almost continuous eruption" [vague] since antiquity. [clarification needed] , in Réunion, erupts frequently enough to be a tourist attraction.

As of 2010 [update] , the longest ongoing (but not necessarily continuous) volcanic eruptive phases are: [58]

Other very active volcanoes include:

    and its neighbor, Nyamuragira, are Africa's most active volcanoes

Dormant and reactivated

It is difficult to distinguish an extinct volcano from a dormant (inactive) one. Dormant volcanoes are those that have not erupted for thousands of years, but are likely to erupt again in the future. [59] [60] Volcanoes are often considered to be extinct if there are no written records of its activity. Nevertheless, volcanoes may remain dormant for a long period of time. For example, Yellowstone has a repose/recharge period of around 700,000 years, and Toba of around 380,000 years. [61] Vesuvius was described by Roman writers as having been covered with gardens and vineyards before its eruption of 79 CE, which destroyed the towns of Herculaneum and Pompeii. Before its catastrophic eruption of 1991, Pinatubo was an inconspicuous volcano, unknown to most people in the surrounding areas. Two other examples are the long-dormant Soufrière Hills volcano on the island of Montserrat, thought to be extinct before activity resumed in 1995, and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE and had long been thought to be extinct.


Extinct volcanoes are those that scientists consider unlikely to erupt again because the volcano no longer has a magma supply. Examples of extinct volcanoes are many volcanoes on the Hawaiian – Emperor seamount chain in the Pacific Ocean (although some volcanoes at the eastern end of the chain are active), Hohentwiel in Germany, Shiprock in New Mexico, US, Zuidwal volcano in the Netherlands, and many volcanoes in Italy such as Monte Vulture. Edinburgh Castle in Scotland is located atop an extinct volcano, called Arthur's Seat. Whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" calderas can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years may be considered dormant instead of extinct.

Volcanic-alert level

The three common popular classifications of volcanoes can be subjective and some volcanoes thought to have been extinct have erupted again. To help prevent people from falsely believing they are not at risk when living on or near a volcano, countries have adopted new classifications to describe the various levels and stages of volcanic activity. [62] Some alert systems use different numbers or colors to designate the different stages. Other systems use colors and words. Some systems use a combination of both.

Volcano warning schemes of the United States

The United States Geological Survey (USGS) has adopted a common system nationwide for characterizing the level of unrest and eruptive activity at volcanoes. The new volcano alert-level system classifies volcanoes now as being in a normal, advisory, watch or warning stage. Additionally, colors are used to denote the amount of ash produced.

The Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas. They are named Decade Volcanoes because the project was initiated as part of the United Nations-sponsored International Decade for Natural Disaster Reduction (the 1990s). The 16 current Decade Volcanoes are

    -Koryaksky (grouped together), Kamchatka, Russia , Jalisco and Colima, Mexico , Sicily, Italy , Nariño, Colombia , Hawaii, US , Central Java, Indonesia , Democratic Republic of the Congo , Washington, US
    , Kagoshima Prefecture, Japan , Guatemala , Cyclades, Greece , Luzon, Philippines , Canary Islands, Spain , New Britain, Papua New Guinea , Nagasaki Prefecture, Japan , Naples, Italy

The Deep Earth Carbon Degassing Project, an initiative of the Deep Carbon Observatory, monitors nine volcanoes, two of which are Decade volcanoes. The focus of the Deep Earth Carbon Degassing Project is to use Multi-Component Gas Analyzer System instruments to measure CO2/SO2 ratios in real-time and in high-resolution to allow detection of the pre-eruptive degassing of rising magmas, improving prediction of volcanic activity. [63]

Volcanic eruptions pose a significant threat to human civilization. However, volcanic activity has also provided humans with important resources.


There are many different types of volcanic eruptions and associated activity: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.

Volcanic gases can reach the stratosphere, where they form sulfuric acid aerosols that can reflect solar radiation and lower surface temperatures significantly. [64] Sulfur dioxide from the eruption of Huaynaputina may have caused the Russian famine of 1601–1603. [65] Chemical reactions of sulfate aerosols in the stratosphere can also damage the ozone layer, and acids such as hydrogen chloride (HCl) and hydrogen fluoride (HF) can fall to the ground as acid rain. Explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon for biogeochemical cycles. [66]

Ash thrown into the air by eruptions can present a hazard to aircraft, especially jet aircraft where the particles can be melted by the high operating temperature the melted particles then adhere to the turbine blades and alter their shape, disrupting the operation of the turbine. This can cause major disruptions to air travel.

A volcanic winter is thought to have taken place around 70,000 years ago after the supereruption of Lake Toba on Sumatra island in Indonesia, [67] This may have created a population bottleneck that affected the genetic inheritance of all humans today. [68] Volcanic eruptions may have contributed to major extinction events, such as the End-Ordovician, Permian-Triassic, and Late Devonian mass extinctions. [69]

The 1815 eruption of Mount Tambora created global climate anomalies that became known as the "Year Without a Summer" because of the effect on North American and European weather. [70] The freezing winter of 1740–41, which led to widespread famine in northern Europe, may also owe its origins to a volcanic eruption. [71]


Although volcanic eruptions pose considerable hazards to humans, past volcanic activity has created important economic resources.

Volcanic ash and weathered basalt produce some of the most fertile soil in the world, rich in nutrients such as iron, magnesium, potassium, calcium, and phosphorus. [72]

Tuff formed from volcanic ash is a relatively soft rock, and it has been used for construction since ancient times. [73] [74] The Romans often used tuff, which is abundant in Italy, for construction. [75] The Rapa Nui people used tuff to make most of the moai statues in Easter Island. [76]

Volcanic activity is responsible for emplacing valuable mineral resources, such as metal ores. [72]

Volcanic activity is accompanied by high rates of heat flow from the Earth's interior. These can be tapped as geothermal power. [72]

The Earth's Moon has no large volcanoes and no current volcanic activity, although recent evidence suggests it may still possess a partially molten core. [77] However, the Moon does have many volcanic features such as maria (the darker patches seen on the moon), rilles and domes.

The planet Venus has a surface that is 90% basalt, indicating that volcanism played a major role in shaping its surface. The planet may have had a major global resurfacing event about 500 million years ago, [78] from what scientists can tell from the density of impact craters on the surface. Lava flows are widespread and forms of volcanism not present on Earth occur as well. Changes in the planet's atmosphere and observations of lightning have been attributed to ongoing volcanic eruptions, although there is no confirmation of whether or not Venus is still volcanically active. However, radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus's highest volcano Maat Mons, in the form of ash flows near the summit and on the northern flank. [79] However, the interpretation of the flows as ash flows has been questioned. [80]

There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth. They include Arsia Mons, Ascraeus Mons, Hecates Tholus, Olympus Mons, and Pavonis Mons. These volcanoes have been extinct for many millions of years, [81] but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well. [81]

Jupiter's moon Io is the most volcanically active object in the solar system because of tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur, sulfur dioxide and silicate rock, and as a result, Io is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1,800 K (1,500 °C). In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io. [82] Europa, the smallest of Jupiter's Galilean moons, also appears to have an active volcanic system, except that its volcanic activity is entirely in the form of water, which freezes into ice on the frigid surface. This process is known as cryovolcanism, and is apparently most common on the moons of the outer planets of the solar system.

In 1989, the Voyager 2 spacecraft observed cryovolcanoes (ice volcanoes) on Triton, a moon of Neptune, and in 2005 the Cassini–Huygens probe photographed fountains of frozen particles erupting from Enceladus, a moon of Saturn. [83] [84] The ejecta may be composed of water, liquid nitrogen, ammonia, dust, or methane compounds. Cassini–Huygens also found evidence of a methane-spewing cryovolcano on the Saturnian moon Titan, which is believed to be a significant source of the methane found in its atmosphere. [85] It is theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar.

A 2010 study of the exoplanet COROT-7b, which was detected by transit in 2009, suggested that tidal heating from the host star very close to the planet and neighboring planets could generate intense volcanic activity similar to that found on Io. [86]

Many ancient accounts ascribe volcanic eruptions to supernatural causes, such as the actions of gods or demigods. To the ancient Greeks, volcanoes' capricious power could only be explained as acts of the gods, while 16th/17th-century German astronomer Johannes Kepler believed they were ducts for the Earth's tears. [87] One early idea counter to this was proposed by Jesuit Athanasius Kircher (1602–1680), who witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal.

Various explanations were proposed for volcano behavior before the modern understanding of the Earth's mantle structure as a semisolid material was developed. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to chemical reactions and a thin layer of molten rock near the surface.


If there was ever a chance for life on the Moon, it ceased to be as its layers cooled and solidified. The lack of volcanic and seismic activity on the crust and mantle has left the Moon an unchanging, dead rock out in space.

Nevertheless, if the plan is to some day have a colony on its surface, we need to continue learning all we can about the layers of the Moon. For now, it’s enough to wonder and snap a few pictures of our closest neighbor while we’re at it.

About Noah Zelvis

Noah is a content writer who has had a love of all things astronomy for as long as he can remember.
When not reaching for the stars, you’ll likely find Noah traveling or running.