Astronomy

How many tsunamis have been caused by meteorites falling?

How many tsunamis have been caused by meteorites falling?


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I don't know if this is a better fit for Earth Science (because of the tsunami part) or for Astronomy (because of the meteorite part).

The Wikipedia page on tsunamis says that tsunamis can be caused the the fall of a meteorite. The first reference after that claim mentions that tsunamis can be caused by meteorites, but in an unsubstantiated way. The second reference is behind a paywall so I can't access it.

How many recorded tsunamis have been caused by the fall of a meteorite?


None in historical times.

A tsunami is caused by a displacement of water, so for a meteorite to cause a measurable tsunami it would have to be very large. The largest known impactor in historic times, in Tunguska, was about 50m diameter could have created waves, but probably not a tsunami. There is evidence that a much larger impact, he Eltanin impact, 2.1 million years ago in the pacific ocean off Chile (a 1.5km diameter impactor) also did not create a tsunami. The waves generated were short wavelength turbulent waves and the energy was lost in friction. Tsunami need to be very long wavelength to cross oceans and cause damage remotely.

Much larger impacts would create tsunami, and the size of the tsunami may exceed that created by earthquakes. See my source Are ocean impacts a serious threat."


Tsunamis in the Caribbean

A tsunami is an ocean wave or series of waves caused by a large-scale disturbance of the ocean floor or surface that abruptly displaces a large mass of water. Tsunamis may be caused by earthquakes, volcanic events, landslides into the sea or impact of stellar objects such as asteroids, comets and meteorites. This article focuses primarily on tsunamis generated by earthquakes and volcanic events. While it is possible for the region to be hit by a tsunami such as the one recently experienced in Asia, scientists currently believe that there is a very low probability of this phenomenon occurring in the Caribbean.

In the past 500 years there have been at least ten earthquake-generated tsunamis in the entire Caribbean which have been reported and verified. Four of these have led to deaths. In total about 350 people in the Caribbean have been killed by these events. These tsunamis occurred as a result of earthquakes in:

  • May 1842, Haiti – An intense local tsunami was believed to have killed up to 200 people in the town of Port-de-Paix. This figure is highly uncertain since total casualties caused by the earthquake were more than 7,000.
  • November 1867, Virgin Islands – Death toll about 20, all in the Virgin Islands
  • October 1918 Puerto Rico – Death toll about 29 in Puerto Rico
  • August 1946 , Dominican Republic – An intense local tsunami which mainly affected the town of Matanzas where up to 100 people were killed

Additional earthquake-generated tsunamis of note also occurred in 1843 affecting Guadeloupe and Antigua and in 1690 in St. Kitts Nevis. The number of casualties related to these tsunamis, if any, is uncertain. In July 2003, a major dome collapse from the Soufriere Hills Volcano in Montserrat caused a tsunami that was experienced in Guadeloupe at about 1m high and in some parts of Montserrat at 4m in amplitude.

Potentially, there are two groups of earthquakes which may generate tsunamis in the Caribbean. These are (1) Earthquakes occurring within the region which may generate local tsunamis (by local we mean that only nearby islands are affected).In the past 500 years there have been approximately 50 potentially tsunamigenic local earthquakes but only 10-20% of these earthquakes actually generated tsunamis that caused significant inundation.(2) Distant earthquakes occurring outside of the region may generate tele-tsunamis.

In November 1755, a major earthquake in the Azores fracture zone near Portugal resulted in a tele-tsunami which crossed the Atlantic and was noticed throughout the eastern Caribbean from Barbados to Antigua and as far west as Cuba. This earthquake is commonly referred to as the Great Lisbon Earthquake. The amplitude of the tsunami in all islands was about 2-3 metres and waves continued to arrive for many hours. No damage or casualties were reported. European sources also reported that the Azores fracture zone generated a second tele-tsunami in March 1761 but no local confirmed observations were made in the Caribbean.

While recent events in Asia have caused much concern over the Caribbean’s vulnerability to tsunamis, it is important to note that all oceans can experience tsunamis but there are more large, destructive tsunamis in the Pacific Ocean because of the many major earthquakes along the margins of the Pacific Ocean and also because dip-slip earthquakes (which involve vertical rather than lateral ground motion) are more common in the Pacific than elsewhere. As a result of the immediacy of the tsunami hazard to countries in the Pacific, there is currently a tsunami early warning system in that region.


Meteorites whipped up mega-tsunamis on Mars

Catastrophic floods, triggered by comets and asteroids smashing into young Mars, helped shape the planet’s landscape – and may help in our hunt for life on the Red Planet. Belinda Smith reports.

The Solar System is no stranger to mega-tsunamis. Just last year, on Earth, scientists analysed unusual boulders sitting 200 metres above sea level on the West African island of Santiago.

The only way those rocks could have ended up on the highlands, they reported in Science Advances, was if a 170-metre wave – pushed along when the oceanic volcano Fogo collapsed 73,000 years ago – dumped them there.

In a 2010 article in Planetary and Space Science , a North American team headed by Canadian Bill Mahaney proposed something similar might have happened on Mars during the Hesperian Period, around 3.4 billion years ago, when it was thought the Red Planet was flush with vast oceans.

But rather than landslides, meteorites could well have forced Martian mega-tsunamis – the Solar System was still being bombarded with asteroids and comets (although not quite on the scale of the Heavy Bombardment which finished around 400 million years earlier).

The problem, though, was tracing ancient Martian coastlines. Mars today lacks liquid water on its surface, let alone oceans. Finding the coasts of these ancient seas, and then locating evidence of huge waves, is tricky.

Mahaney and colleagues suggested the best places to start might be the Chryse Planitia and Arabia Terra regions of the northern plains – some of the oldest, most heavily cratered terrains on the planet.

Rodriguez and colleagues examined infrared (or thermal) images of those areas and found what appeared to be coastal boundaries – thermally dark sediments abutting bright, bouldered, rocky segments – on different elevations.

Left: Colour-coded digital elevation model of the study area showing the two proposed shoreline levels of an early Mars ocean that existed approximately 3.4 billion years ago. Right: Areas (in brown) covered by the documented tsunami events extending from these shorelines.
Alexis Rodriguez

These are evidence of two tsunamis: one which covered around 800,000 square kilometres and extended around 530 kilometres inland, and another that covered a million square kilometres with a reach of around 650 kilometres.

The second flowed further because, over the intervening few million years since the first, the plain eroded and smoothed, easing the wave’s passage. It also dumped huge chunks of ice inland.

To reach such distances, both tsunamis were around 50 metres tall when they hit shore, and as tall as 120 metres in parts.

The team also saw what seemed to be backwash channels. Like those found on Earth when a tsunami’s water is dragged back to sea by gravity, the Martian channels were perpendicular to the ancient shoreline.

Simulations then showed the meteorites responsible for such massive waves would have left impact craters around 30 kilometres wide.

The team saw seven impact craters in the region fit the bill, which turned out to be two such meteorites every 30 million years for the area at the time, or one every three million years striking anywhere on Mars.

Tracing mega-tsunami flows can help scientists nail down targets to search for life, says study co-author Alberto Fairén: “In spite of the extremely cold and dry global climatic conditions, the early Martian ocean likely had a briny composition that allowed it to remain in liquid form for as long as several tens of millions of years.

“Subfreezing briny aqueous environments are known to be habitable environments on Earth, and consequently, some of the tsunami deposits might be prime astrobiological targets.”

Belinda Smith

Belinda Smith is a science and technology journalist in Melbourne, Australia.

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Meteorite Minerals Hint at Earth Extinctions, Climate Change

A huge asteroid that wiped out the dinosaurs may not have been the only cosmic event to cause mass extinctions or change Earth’s climate. Tiny minerals leftover from many smaller meteorites could provide the geological evidence needed to show how rocks falling from the sky changed the course of life’s evolution on our planet more than just once.

The tiny minerals called spinels — about the size of a sand grain — can survive the harshest weather and chemical changes on Earth’s surface. Swedish researchers hope to collect enough of the spinels in different parts of the world to connect the dots between the breakup of huge asteroids in space and certain extinction or climate events during Earth’s history.

"I think it would be very interesting if our spinel approach in the long run could provide empirical evidence for how asteroid showers in the inner solar system correlate with the onset of ice ages," Birger Schmitz, a marine geologist at Lund University in Sweden, said. [Potentially Dangerous Asteroids (Images)]

The hunt for spinels has led Schmitz and his colleagues to dissolve tons of rocks in acid over the past decade or so — many of the rocks originating from a commercial limestone quarry in Thorsberg, Sweden. Such a tactic could reveal convincing patterns in the geological records that scientists cannot piece together from the occasional fossilized meteorite or rare impact crater.

Without a trace

Most meteorites that have fallen to Earth end up disappearing without becoming fossilized or leaving an impact crater for scientists to find. That has made it virtually impossible for scientists to recover enough evidence to back theories about how astronomical events have tied into Earth’s history.

"We know that in desert areas on Earth, meteorites typically decompose within 20 [thousand] to 30,000 years," Schmitz said. "In wetter areas, decomposition goes faster."

But the vanishing meteorites do leave behind different types of spinels, including extremely tough chromium or alumina oxides. The chemical and isotopic fingerprints of such spinels reveal what type of meteorites they originate from. Scientists now know that extraterrestrial spinel minerals can be found in the layers of built-up sediment of almost any age over the past 3.5 billion years.

Such spinels can reveal differences in the rate and types of meteorites falling to Earth at different times in the planet’s history, Schmitz said in the June issue of the journal Chemie der Erde. They could also reveal more about the chemical makeup of asteroids, or help scientists understand if any asteroid breakups affected life on Earth in the past.

Beyond dinosaur extinction

The spinel record could reveal more extinction events with extraterrestrial links than just the mass dinosaur extinction. An earlier mass extinction during the Frasnian-Fammenian period about 372 million years ago coincides with at least three large impact craters.

"There are many large craters on Earth associated with this event, but no close connection between one large impact and the extinction event has yet been shown," Schmitz said.

But falling space rocks may bring more than just destruction to Earth. Perhaps the greatest explosion of new ocean life in Earth’s history took place during the Great Ordovician Biodiversification Event about 470 million years ago — a period coinciding with the largest known asteroid breakup in the solar system’s asteroid belt over the last 3 billion years.

Schmitz and colleagues discovered a rapid increase in the number of spinels found in the limestone rock layers marking the start of that diversification period at sites in Sweden, western Russia and central China. They speculate that the asteroid breakup led to frequent impacts on Earth by kilometer-sized asteroids that could have spawned the resulting changes in the diversity of life. [Wipe Out: History's Most Mysterious Extinctions (Countdown)]

Another theory links asteroid showers to Earth’s three most recent major ice ages that occurred about every 250 to 300 million years. No definitive proof exists yet, but the ice age periods roughly coincide with the sun’s orbit around the galaxy every 225 to 250 million years — an event that could expose Earth to more frequent meteorite falls at certain periods. The study of spinels could help prove such theories right or wrong in the coming years.

Lab science on acid

Building a record of Earth’s history through extraterrestrial spinels still represents a fairly new idea, despite scientists having known about spinels for several decades. But Schmitz is looking forward to continuing the hunt for spinels with a specially designed lab at Lund University.

The new lab will use acid to dissolve about 5 to 10 tons of sedimentary limestone per year in search of spinels — a big step up from how Schmitz’s group handled just over one tenth of a ton per year about 15 years ago. Industrial-grade lab equipment includes acid-resistant pumps for injecting acid into large plastic barrels holding different rock samples.

Schmitz’s approach has slowly won over skeptics in the meteorite research community, said Philipp Heck, associate curator of meteoritics and polar studies at the Field Museum of Natural History in Chicago. He added that the spinel approach would prove most effective when sediment layers representing past ages of the Earth are highly condensed and the rate of meteorites hitting the Earth was much higher than it is today.

"This is certainly a very useful approach to study the extraterrestrial record of ordinary chondrites in sediments," Heck said. "This approach needs now to be applied to different types of meteorites."

But geologists won’t need an entirely new lab to start getting in on the action by tackling smaller amounts of rocks that could hold hidden extraterrestrial treasure.

"The best thing is that all you need for the identification of the extraterrestrial spinels is a regular scanning electron microscope with an attached standard-type element identification system (EDS)," Schmitz said. "Most geology departments have this equipment."


Contents

Tsunami

The term "tsunami" is a borrowing from the Japanese tsunami 津波 , meaning "harbour wave." For the plural, one can either follow ordinary English practice and add an s, or use an invariable plural as in the Japanese. [14] Some English speakers alter the word's initial /ts/ to an /s/ by dropping the "t," since English does not natively permit /ts/ at the beginning of words, though the original Japanese pronunciation is /ts/ .

Tidal wave

Tsunamis are sometimes referred to as tidal waves. [15] This once-popular term derives from the most common appearance of a tsunami, which is that of an extraordinarily high tidal bore. Tsunamis and tides both produce waves of water that move inland, but in the case of a tsunami, the inland movement of water may be much greater, giving the impression of an incredibly high and forceful tide. In recent years, the term "tidal wave" has fallen out of favour, especially in the scientific community, because the causes of tsunamis have nothing to do with those of tides, which are produced by the gravitational pull of the moon and sun rather than the displacement of water. Although the meanings of "tidal" include "resembling" [16] or "having the form or character of" [17] tides, use of the term tidal wave is discouraged by geologists and oceanographers.

A 1969 episode of the TV crime show Hawaii Five-O entitled "Forty Feet High and It Kills!" used the terms "tsunami" and "tidal wave" interchangeably. [18]

Seismic sea wave

The term seismic sea wave is also used to refer to the phenomenon, because the waves most often are generated by seismic activity such as earthquakes. [19] Prior to the rise of the use of the term tsunami in English, scientists generally encouraged the use of the term seismic sea wave rather than tidal wave. However, like tsunami, seismic sea wave is not a completely accurate term, as forces other than earthquakes—including underwater landslides, volcanic eruptions, underwater explosions, land or ice slumping into the ocean, meteorite impacts, and the weather when the atmospheric pressure changes very rapidly—can generate such waves by displacing water. [20] [21]

While Japan may have the longest recorded history of tsunamis, the sheer destruction caused by the 2004 Indian Ocean earthquake and tsunami event mark it as the most devastating of its kind in modern times, killing around 230,000 people. [22] The Sumatran region is also accustomed to tsunamis, with earthquakes of varying magnitudes regularly occurring off the coast of the island. [23]

Tsunamis are an often underestimated hazard in the Mediterranean Sea and parts of Europe. Of historical and current (with regard to risk assumptions) importance are the 1755 Lisbon earthquake and tsunami (which was caused by the Azores–Gibraltar Transform Fault), the 1783 Calabrian earthquakes, each causing several tens of thousands of deaths and the 1908 Messina earthquake and tsunami. The tsunami claimed more than 123,000 lives in Sicily and Calabria and is among the most deadly natural disasters in modern Europe. The Storegga Slide in the Norwegian Sea and some examples of tsunamis affecting the British Isles refer to landslide and meteotsunamis predominantly and less to earthquake-induced waves.

As early as 426 BC the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause. [12] [13]

The cause, in my opinion, of this phenomenon must be sought in the earthquake. At the point where its shock has been the most violent the sea is driven back, and suddenly recoiling with redoubled force, causes the inundation. Without an earthquake I do not see how such an accident could happen. [24]

The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15–19) described the typical sequence of a tsunami, including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave, after the 365 AD tsunami devastated Alexandria. [25] [26]

The principal generation mechanism of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. [27] This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests. [28] [29] However, the possibility of a meteorite causing a tsunami is debated. [30]

Seismicity

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crustal deformation when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. [31] More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. Movement on normal (extensional) faults can also cause displacement of the seabed, but only the largest of such events (typically related to flexure in the outer trench swell) cause enough displacement to give rise to a significant tsunami, such as the 1977 Sumba and 1933 Sanriku events. [32] [33]

Over-riding plate bulges under strain, causing tectonic uplift.

Plate slips, causing subsidence and releasing energy into water.

The energy released produces tsunami waves.

Tsunamis have a small wave height offshore, and a very long wavelength (often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres), [34] which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimetres (12 in) above the normal sea surface. They grow in height when they reach shallower water, in a wave shoaling process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas.

On April 1, 1946, the 8.6 Mw Aleutian Islands earthquake occurred with a maximum Mercalli intensity of VI (Strong). It generated a tsunami which inundated Hilo on the island of Hawaii with a 14-metre high (46 ft) surge. Between 165 and 173 were killed. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska.

Examples of tsunamis originating at locations away from convergent boundaries include Storegga about 8,000 years ago, Grand Banks in 1929, and Papua New Guinea in 1998 (Tappin, 2001). The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilised sediments, causing them to flow into the ocean and generate a tsunami. They dissipated before travelling transoceanic distances.

The cause of the Storegga sediment failure is unknown. Possibilities include an overloading of the sediments, an earthquake or a release of gas hydrates (methane etc.).

The 1960 Valdivia earthquake (Mw 9.5), 1964 Alaska earthquake (Mw 9.2), 2004 Indian Ocean earthquake (Mw 9.2), and 2011 Tōhoku earthquake (Mw9.0) are recent examples of powerful megathrust earthquakes that generated tsunamis (known as teletsunamis) that can cross entire oceans. Smaller (Mw 4.2) earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can devastate stretches of coastline, but can do so in only a few minutes at a time.

Landslides

In the 1950s, it was discovered that tsunamis larger than had previously been believed possible can be caused by giant submarine landslides. These large volumes of rapidly displaced water transfer energy at a faster rate than the water can absorb. Their existence was confirmed in 1958, when a giant landslide in Lituya Bay, Alaska, caused the highest wave ever recorded, which had a height of 524 metres (1,719 ft). [35] The wave did not travel far as it struck land almost immediately. The wave struck three boats—each with two people aboard—anchored in the bay. One boat rode out the wave, but the wave sank the other two, killing both people aboard one of them. [36] [37] [38]

Another landslide-tsunami event occurred in 1963 when a massive landslide from Monte Toc entered the reservoir behind the Vajont Dam in Italy. The resulting wave surged over the 262-metre (860 ft)-high dam by 250 metres (820 ft) and destroyed several towns. Around 2,000 people died. [39] [40] Scientists named these waves megatsunamis.

Some geologists claim that large landslides from volcanic islands, e.g. Cumbre Vieja on La Palma (Cumbre Vieja tsunami hazard) in the Canary Islands, may be able to generate megatsunamis that can cross oceans, but this is disputed by many others.

In general, landslides generate displacements mainly in the shallower parts of the coastline, and there is conjecture about the nature of large landslides that enter the water. This has been shown to subsequently affect water in enclosed bays and lakes, but a landslide large enough to cause a transoceanic tsunami has not occurred within recorded history. Susceptible locations are believed to be the Big Island of Hawaii, Fogo in the Cape Verde Islands, La Reunion in the Indian Ocean, and Cumbre Vieja on the island of La Palma in the Canary Islands along with other volcanic ocean islands. This is because large masses of relatively unconsolidated volcanic material occurs on the flanks and in some cases detachment planes are believed to be developing. However, there is growing controversy about how dangerous these slopes actually are. [41]

Meteorological

Some meteorological conditions, especially rapid changes in barometric pressure, as seen with the passing of a front, can displace bodies of water enough to cause trains of waves with wavelengths. These are comparable to seismic tsunamis, but usually with lower energies. Essentially, they are dynamically equivalent to seismic tsunamis, the only differences being 1) that meteotsunamis lack the transoceanic reach of significant seismic tsunamis, and 2) that the force that displaces the water is sustained over some length of time such that meteotsunamis cannot be modelled as having been caused instantaneously. In spite of their lower energies, on shorelines where they can be amplified by resonance, they are sometimes powerful enough to cause localised damage and potential for loss of life. They have been documented in many places, including the Great Lakes, the Aegean Sea, the English Channel, and the Balearic Islands, where they are common enough to have a local name, rissaga. In Sicily they are called marubbio and in Nagasaki Bay, they are called abiki. Some examples of destructive meteotsunamis include 31 March 1979 at Nagasaki and 15 June 2006 at Menorca, the latter causing damage in the tens of millions of euros. [42]

Meteotsunamis should not be confused with storm surges, which are local increases in sea level associated with the low barometric pressure of passing tropical cyclones, nor should they be confused with setup, the temporary local raising of sea level caused by strong on-shore winds. Storm surges and setup are also dangerous causes of coastal flooding in severe weather but their dynamics are completely unrelated to tsunami waves. [42] They are unable to propagate beyond their sources, as waves do.

Man-made or triggered tsunamis

There have been studies of the potential of the induction of and at least one actual attempt to create tsunami waves as a tectonic weapon.

In World War II, the New Zealand Military Forces initiated Project Seal, which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park the attempt failed. [43]

There has been considerable speculation on the possibility of using nuclear weapons to cause tsunamis near an enemy coastline. Even during World War II consideration of the idea using conventional explosives was explored. Nuclear testing in the Pacific Proving Ground by the United States seemed to generate poor results. Operation Crossroads fired two 20 kilotonnes of TNT (84 TJ) bombs, one in the air and one underwater, above and below the shallow (50 m (160 ft)) waters of the Bikini Atoll lagoon. Fired about 6 km (3.7 mi) from the nearest island, the waves there were no higher than 3–4 m (9.8–13.1 ft) upon reaching the shoreline. Other underwater tests, mainly Hardtack I/Wahoo (deep water) and Hardtack I/Umbrella (shallow water) confirmed the results. Analysis of the effects of shallow and deep underwater explosions indicate that the energy of the explosions does not easily generate the kind of deep, all-ocean waveforms which are tsunamis most of the energy creates steam, causes vertical fountains above the water, and creates compressional waveforms. [44] Tsunamis are hallmarked by permanent large vertical displacements of very large volumes of water which do not occur in explosions.


Volcano World

A tsunami is a huge sea wave, or also known as a seismic sea-wave. They are very tall and height and have extreme power. A tsunami is formed when there is ground uplift and quickly following a drop. From this, the water column is pushed up above the average sea level. Volcanic tsunamis can result from violent submarine explosions. They can also be caused by caldera collapses, tectonic movement from volcanic activity, flank failure into a water source or pyroclastic flow discharge into the sea. As the wave is formed, it moves in a vertical direction and gains great speeds in deeper waters and can reach speeds as fast as 650 mph. In shallow water it can still be as fast as 200mph. They travel over the continental shelf and crash into the land. This power doesn’t decrease when they hit land though, there is an extreme amount of energy when the water travels back towards its source. Approximately 5 percent of tsunamis are formed from volcanoes and approximately 16.9 percent of volcanic fatalities occur from tsunamis. (Tanguy, J.C. 1998)

Image 1 - This image shows how the eruption of a volcano on a waters edge causes a tsunami to form.

The debris avalance crashes into the sea once it travels down the volcanoes side pushing the water up as they meet. (Springer,L. 2005.).

Image 2 - This is a cartoon showing the uplift and drop of the ground.

As you can see, from this motion, the wave travels across the water growing in height until it hits a continent. (Springer,L. 2005.).

Tsunamis can affect an area larger than most other volcanic effects greater than 25 km. These waves are great in size and power when heading towards land or boats but are miniscule out in open water. (Thorarinsson, S. 1979.) (Latter, J.H. 1981.) Deposits from tsunamis are generally thin layers of sand that go much further than the original tide’s edge. These sand deposits are taken from the tidal zone and transported inland during the occurrence of the tsunami. As the water recedes, it drags along sediments from inland back into the water source. The deposits are poorly sorted and many times contain pumice and lithic grains from the eruption.

Image 3 - This just shows an example of how far and how large tsunami waves can grow even though its initial

souce may not have been a large collapse. (Unknown author. 2000.).

On August 27, 1883, when Krakatoa erupted, it caused the largest and most disastrous volcanic tsunami in history. It grew to be as big as 40 meters tall. The wave was formed just under a minute after the explosion, and then close to fifteen minutes later an air wave formed with great power. Sea levels rose and fell all over the world rose. (Choi, B.H. 2003.). This tsunami is through to have killed over thirty six thousand people and countless livestock. (Tanguy, J.C. 1998). There was a second explosion when the magma chamber collapsed allowing sea water to rush into the magma chamber forming a second, but smaller tsunami. This one was only about 10 meters in height.

Image 4 - This image shows where the flank and rock fell into the water and where the giant tsunami formed.

You can see where it radiated out from the source and continued to travel across the oceans.

Red shows where it is strongest and green shows where it is the weakest, yet still considered a tsunami. Choi, B.H. 2003.).

The island of Thera, also known as Santorini, in Greece erupted 3600 B.P. during what is known as the Late Bronze Age. It was one of five volcanic islands located along the Hellenic arc. The caldera collapsed into the sea and the giant wave traveled across the Southern Aegean Sea as far as the western coasts of Turkey and Crete. Deposits contained macro and microfossils from deep-sea sediments and there was evidence of pyroclastic material and a lot of pumice. These sediments are known as homogenites. It was later realized that the graded deposits were well sorted and were overlain by tephra fallout from a later eruption. (Carey, S. 2001) The wave grew to be over 17 meters at its highest and 1.9 meters when it was just starting to form. In other areas nearby, waves grew to be between 7 and 12 meters in height. (McCoy and Heiken, 2000.). Much of the area directly surrounding Thera collapsed from the pressure of the waves or were weathered away from pyroclastic material. Now, you can only see some of what is left of the dome sticking out from the water. There are no current estimates of the number of fatalities in the region.

Image 5 - This image shows where the caldera collapsed and formed the initial tuff ring.

From the large amount of rock and ash falling into the ocean, the tsunami formed.

Now, there is only evidence of pieces of the caldera left above water. (McCoy and Heiken, 2000.).


Study: Today’s Rare Meteorites Were Common in Ordovician Period

This is an artist’s rendering of the space collision 466 million years ago that gave rise to many of the meteorites falling today. Image credit: Don Davis, Southwest Research Institute.

Around 466 million years ago (Ordovician period), there was a giant collision in our Solar System. Something hit an asteroid and broke it apart, sending chunks of rock falling to Earth as meteorites.

But what kinds of meteorites were making their way to our planet before that collision?

A research team led by Field Museum scientist Philipp Heck has tackled that question by creating the first reconstruction of the distribution of meteorite types before the collision.

The scientists discovered that most of the meteorites we see today are rare, while many meteorites that are rare today were common before the collision.

The discovery confirms a hypothesis presented in 2016 when Lund University Professor Birger Schmitz revealed that he had found a so-called ‘fossil’ meteorite.

The meteorite was given the name Osterplana 065 and was discovered in a quarry outside Lidköping in Sweden. The term ‘fossil’ was used because of its unusual composition, different from all known groups of meteorites, and because it originated from a celestial body that was destroyed in ancient times.

The discovery led to the hypothesis that the flow of meteorites may have been completely different 466 million years ago.

“The new results confirm this hypothesis,” said Prof. Schmitz, co-author on the current study.

“Based on 43 micrometeorites, which are as old as Osterplana 065, our new study shows that back then the flow was actually dramatically different.”

“The conventional view is that the Solar System has been very stable over the past 500 million years. So it is quite surprising that the meteorite flow at 466 million years ago was so different from the present,” he added.

Dr. Heck, Prof. Schmitz and their colleagues retrieved samples of rock from an ancient seafloor that contained micrometeorites, and then dissolved the rocks in acid so that only microscopic chromite crystals remained.

“Chrome-spinels, crystals that contain the mineral chromite, remain unchanged even after hundreds of millions of years,” Dr. Heck said.

“Since they were unaltered by time, we could use these spinels to see what the original parent body that produced the micrometeorites was made of.”

Analysis of the chemical makeup of the spinels showed that the meteorites and micrometeorites that fell earlier than 466 million years ago are different from the ones that have fallen since.

A full 34% of the pre-collision meteorites belong to a meteorite type called primitive achondrites today, only 0.45% of the meteorites that land on Earth are this type.

Other ancient micrometeorites sampled turned out to be relics from the asteroid Vesta, which underwent its own collision event over a billion years ago.

“Meteorite delivery from the asteroid belt to the Earth is a little like observing landslides started at different times on a mountainside,” said co-author Dr. William Bottke, of the Southwest Research Institute.

“Today, the rocks reaching the bottom of the mountain might be dominated by a few recent landslides. Going back in time, however, older landslides should be much more important.”

“The same is true for asteroid breakup events some younger ones dominate the current meteorite flux, while in the past older ones dominated.”

“Knowing more about the different kinds of meteorites that have fallen over time gives us a better understanding of how the main asteroid belt evolved and how different collisions happened,” Dr. Heck added.

“Ultimately, we want to study more windows in time, not just the area before and after this collision during the Ordovician period, to deepen our knowledge of how different bodies in Solar System formed and interact with each other.”


The physics of a tsunami

Tsunamis can have wavelengths ranging from 10 to 500 km and wave periods of up to an hour. As a result of their long wavelengths, tsunamis act as shallow-water waves. A wave becomes a shallow-water wave when the wavelength is very large compared to the water depth. Shallow-water waves move at a speed, c, that is dependent upon the water depth and is given by the formula:

where g is the acceleration due to gravity (= 9.8 m/s 2 ) and H is the depth of water.

In the deep ocean, the typical water depth is around 4000 m, so a tsunami will therefore travel at around 200 m/s, or more than 700 km/h.

For tsunamis that are generated by underwater earthquakes, the amplitude of the tsunami is determined by the amount by which the sea-floor is displaced. Similarly, the wavelength and period of the tsunami are determined by the size and shape of the underwater disturbance.

As well as travelling at high speeds, tsunamis can also travel large distances with limited energy losses. As the tsunami propagates across the ocean, the wave crests can undergo refraction (bending), which is caused by segments of the wave moving at different speeds as the water depth along the wave crest varies.


How many tsunamis have been caused by meteorites falling? - Astronomy

How many meteorites hit the earth each year, and how do they determine that?

It's a bit hard to tell exactly how many meteorites hit Earth each year. Most meteors that you see in the sky are caused by pea-sized pieces of rock and there's a lot of stuff this size in the solar system that Earth can run into! We can estimate the number of meteorites per year by carefully monitering the meteorites per day in one area, for example by using an all-sky camera to image the meteors visible in a given location, and then assume that all areas get roughly the same number of meteorites and add up the total.

Another way to tell how many meteorites hit Earth each year is to look at the number of meteorites found in dry regions where there isn't much vegtation or erosion (like deserts), where you expect to be able to find most of the meteorites that fell. We can get an estimate of how long ago the meteorite fell to Earth by looking at how it's been weathered, or altered by Earth's atmosphere and the local climate. Then we can plot how many meteorites fell at that region per year.

However, I can still find a lot of different estimates for how much stuff hits Earth each year, partly because different studies look at different size ranges, and all the procedures have errors. Estimates for the mass of material that falls on Earth each year range from 37,000-78,000 tons. Most of this mass would come from dust-sized particles.

A study done in 1996 (looking at the number of meteorites found in deserts over time) calculated that for objects in the 10 gram to 1 kilogram size range, 2900-7300 kilograms per year hit Earth. However, unlike the number above this does not include the small dust particles. They also estimate between 36 and 166 meteorites larger than 10 grams fall to Earth per million square kilometers per year. Over the whole surface area of Earth, that translates to 18,000 to 84,000 meteorites bigger than 10 grams per year. But most meteorites are too small to actually fall all the way to the surface. (This study was led by P. A. Bland and was published in Monthly Notices of the Royal Astronomical Society.)


How many tsunamis have been caused by meteorites falling? - Astronomy

How many meteorites hit the earth each year, and how do they determine that?

It's a bit hard to tell exactly how many meteorites hit Earth each year. Most meteors that you see in the sky are caused by pea-sized pieces of rock and there's a lot of stuff this size in the solar system that Earth can run into! We can estimate the number of meteorites per year by carefully monitering the meteorites per day in one area, for example by using an all-sky camera to image the meteors visible in a given location, and then assume that all areas get roughly the same number of meteorites and add up the total.

Another way to tell how many meteorites hit Earth each year is to look at the number of meteorites found in dry regions where there isn't much vegtation or erosion (like deserts), where you expect to be able to find most of the meteorites that fell. We can get an estimate of how long ago the meteorite fell to Earth by looking at how it's been weathered, or altered by Earth's atmosphere and the local climate. Then we can plot how many meteorites fell at that region per year.

However, I can still find a lot of different estimates for how much stuff hits Earth each year, partly because different studies look at different size ranges, and all the procedures have errors. Estimates for the mass of material that falls on Earth each year range from 37,000-78,000 tons. Most of this mass would come from dust-sized particles.

A study done in 1996 (looking at the number of meteorites found in deserts over time) calculated that for objects in the 10 gram to 1 kilogram size range, 2900-7300 kilograms per year hit Earth. However, unlike the number above this does not include the small dust particles. They also estimate between 36 and 166 meteorites larger than 10 grams fall to Earth per million square kilometers per year. Over the whole surface area of Earth, that translates to 18,000 to 84,000 meteorites bigger than 10 grams per year. But most meteorites are too small to actually fall all the way to the surface. (This study was led by P. A. Bland and was published in Monthly Notices of the Royal Astronomical Society.)


Watch the video: If an Asteroid Falls in the Ocean, Will It Cause a Tsunami? (November 2022).