Description

Lonar crater has formed in the approximately 65 million years old Deccan Trap basalt. Layer of basalt here is approximately 400 m thick. Research shows that initially this crater was approximately 230 – 245 m deep, but now it is less than 150 m deep.

Crater has slightly oval form, with a diameter of 1,800 m.

Inner slopes of crater are 5 – 25° steep.

Lonar crater has distinct rims and is visually one of most prominent impact craters on Earth.

Meteorite impact

At some time specialists considered that this crater was created by an eruption of volcano but now it is proved that meteorite impact is the cause. There have been found the characteristic planar deformation structures in the grains of feldspar, shatter cones. Around the crater is ejecta blanket – layer of debris, which fell on the ground after the impact. Tectites – pieces of melted silica – have also been found.

Meteorite most likely came from the east, it hit the ground at 30 – 45° tilt.

Earlier, basing on the data of thermoluminescence analyses, it was believed that meteorite fell 52 thousand years ago.

Recent studies ⁴⁰Ar/³⁹Ar analysis though show a different age – 570 000 ± 47,000 years (1, 2). This method seems to be more reliable, also the crater seems to be too much eroded for a period of 50,000 years.

This is the only impact crater fully created in basaltic rock. Research of Lonar crater provides valuable information about the consequences of meteoritic impact on such planets as Mars.

Ambar lake – another impact crater?

700 m to the north of Lonar crater is located smaller crater – Ambar lake crater (Little Lonar).

Ambar lake also is oval shaped, with 250 – 290 m diameter, with approximately 6 m high rim around it. Lake is located some 5 m below the rim.

Although it is speculated that this smaller crater might have been created by the debris from the large crater, it most likely was created by another piece of meteorite – thus this is one more impact crater.

Lonar lake

In the large crater, 137 m below the crater rim is located a unique lake – Lonar lake. The diameter of this shallow lake is 1.2 km. The uniqueness of the lake is defined by the following factors:

• This is the only lake in the world, which is located in basaltic meteorite crater;
• Tall rims of crater protect the lake from the impact of winds, different parts of the lake do not get mixed, lake basin has its own regime of increased humidity and temperature.

Lonar lake is a saline soda lake with a high content of dissolved carbonates. The salinity of the lake is fluctuating – in the dry period the lake level falls and salinity increases, in the rainy period level rises and water is less salty.

Near the banks of the lake are several freshwater springs – due to this and due to small streams of rainwater the water near the shore is less saline. Near the shores pH of water is neutral – 7, but in the middle water can be very saline and pH can reach 11.

Unusual ecosystem

Each zone in the lake has its own ecosystem. More unusual is the life in the centre – in alkaline zone, where live specific microorganisms, e.g. Halomonas sp., Paracoccus sp. Klebsiella sp., Slackia sp. Actinopolyspora sp.. Some of these microorganisms can survive only in a very alkaline environment and can survive in inorganic environments. These microorganisms are capable to fix atmospheric nitrogen.

Outer zone of the lake is more friendly to common inhabitants of lakes in India – here are seen numerous wading birds, along the shores are seen lizards, gazelles, and other animals. For several centuries local people are mining salts from the lake.

Slopes of the lake also have their own, specific ecosystem. Around the lake is a belt of alkaline mud, which is inundated in rainy periods.

Further grows a belt of acacia trees and then starts jungle with tamarinds, teak trees, and other trees.

Temples

India is a land of temples and the Lonar crater is not an exception. It seems this unusual lake has been sacred for a long time. Currently at the banks of the lake are eight temples – Vishnumandir, Wagh Mahadev, Mora Mahadev, Munglyacha Mandir, Goddess Kamalaja Devia, and three more temples. Some are located higher above the lake, some are partly inundated. Best preserved is Kamalaja Devi temple, which is adorned with sculptures.

Endangered lake

This unique lake with its fragile ecosystem is endangered. India is densely populated and, unfortunately, this density creates increasing problems – the lake is increasingly polluted with sewage from the nearby villages, it happens that trees on the slopes are felled, grazing animals come here. Religious festivities take place at the lake and guests leave garbage and graffiti here.

Crater is protected as a geological landmark, but the protection regime for this unique natural landmark should be more strict and adapted to its specifics. There are initiative to improve the situation (E.g. "Save Lonar") – let’s hope that the unique qualities of the lake will be preserved for future generations.

References

1. F. Jourdan, F. Moynier, C. Koeberl. First ⁴⁰Ar/³⁹Ar Age of the Lonar Crater: a ˜0.65 MA Impact Event?., 41st Lunar and Planetary Science Conference (2010). Accessed on December 29, 2012.
2. F. Jourdan, F. Moynier, C. Koeberl, S. Eroglu. ⁴⁰Ar/³⁹Ar age of the Lonar crater and consequence for the geochronology of planetary impacts. Geology July 2011 v. 39, no. 7, p. 671-674. Accessed on December 29, 2012.

Lonar crater is included in the following articles:

Meteoroid

Some 30 – 50 m large meteoroid (e.g. object which is larger than a meteorite but smaller than an asteroid) hit the savanna near the present-day Pretoria some 220 000 years ago. There are ongoing discussions about the age of the crater – some researchers consider that its age might exceed 300 000 years.

Meteoroid fell with a speed of 20 – 30 km per second and when it hit the 2.06 billion years old granite of Bushveld complex, its kinetic energy turned into an explosion. The energy of this blast was equivalent to 20 – 40 megatons of TNT – like 1000 atomic bombs of Hiroshima type.

Area of some 1000 km² was turned into a desert. It has been calculated that such an impact could create extreme wind with a speed over 1000 km/s and felling trees up to 14 – 19 km far away. Burn damage could spread up to 10 km far.

It is well possible that early humans were living in this area and were exposed to this catastrophe.

Meteoroid itself most likely was chondrite, e.g. it consisted of stone. No parts of it have been found – it turned into vapor during the impact.

Size of crater

Rather soon the freshly created crater cooled down, vegetation returned. Since its creation, the rims of the crater eroded and became less steep. There are not that many proofs of impact left, just large pieces of granite are thrown up to hundreds of meters from the crater rim.

Rims of the crater today rise 60 m above the surroundings. The diameter of the crater is 1,130 m, current depth below the rims is up to 119 m.

Bed of crater is covered with 90 m thick sediments. Thus the total depth of the crater is some 180 m if counted from the crater rims or approximately 120 m below the surroundings.

Salt lake

Name of the crater in the local Tswana language means "Place of Salt". Also, Europeans named it after the lake in it – Saltpan.

This small lake at the bottom of the crater has a diameter of some 300 m, it is less than 3 m deep. Lake has no outlets or inlets, it is fed by rainwater and groundwater. Over time carbonate and sodium chloride salts have accumulated and Tswaing Lake is hypersaline, with a pH around 10.

This lake is a subject of several local legends, including a legend about monstrous watersnake. In reality, only algae and one species of salt-tolerant plants survive in this salty water.

Lake deposits have recorded the climate history of the last 190 000 years – research of this valuable scientific asset continues.

History

Man-made stone tools next to this lake are at least 100,000 years old – back then people most likely were hunting there. Much later local Tswana and Sotho people collected the salt from this lake. They did it for many centuries, at least since 1200 AD.

Initiative was taken over by Europeans and in 1912 – 1956 a company "SA Alkali Ltd." pumped the brine from the floor of the crater as a raw material for obtaining salt and soda.

Meanwhile a scientific discussion was ongoing between those who considered that this is a volcanic crater (Wagner, 1922) and those who believed that this is an impact crater (Rohleder, 1933). Only the data from boreholes in 1989 – 1990 proved the impact origin of the Tswaing crater. In these times a dam was built in the lake for drilling equipment.

Today Tswaing crater is a beloved tourist destination. In 1996 here opened a museum – the third museum next to impact crater after Meteor Crater Visitor Centre next to Barringer crater in Arizona, United States and Kaali crater museum in Estonia. The first geopark in Africa has been established here as well.

Tswaing crater is included in the following articles:

Amguid crater has formed in Lower Devonian sandstone in a remote part of Sahara, more than one hundred kilometers from the nearest inhabited place. One can not reach this place in a car. Travelers should walk towards the crater along guelta – a deep river valley with occasional pools of water. This area is pristine – with a wealth of prehistoric (unexplored!) landmarks and undisturbed wildlife.

Amguid crater was mentioned in the scientific literature in 1953 (1) by French explorer Roman Karpoff – he noted that he has noticed a possible impact crater from a plane in 1948. French geologist Jean-Phillippe Lefranc reached the crater in the late 1960s.

As the crater looks little eroded and "fresh", scientists consider that it is younger than 100 thousand years but older than 10 thousand years. There is no research yet which would provide more exact data.

Nevertheless the structure of the crater clearly shows that this is an impact crater. The crater is almost perfectly circular, with steep walls. Amguid crater has raised rims, which are covered with sandstone blocks, often several meters in diameter. Research from space hints that ejecta fell mainly to the north-north-east, thus it is probable that meteorite was falling from the south-south-west.

Diameter of the crater (as measured in Google Earth) is 500 – 530 m, the approximate depth between the bottom of the crater and its rims is 65 m.

Crater has been partly filled with wind-blown sand – thus far we do not know the real depth of the crater below the layer of this sand. The central part of the Amguid crater is flat, covered with aeolian silts. These silts refract the light – due to this from the space it looks as if the crater has a white area in the center.

There are no reports of parts of meteorite from this crater but among the collectors in very small amounts is sold the exotic Amguid Crater Glass or Golden Moldavite – a melted glass in rare golden color.

References

1. Roman Karpoff. The meteorite crater of Talemzane in Southern Algeria. Meteoritics, Volume 1., number 1. p.31. (1953)

Amguid crater is included in the following articles:

History

This crater is located in Sperrgebiet – a restricted area of Namibia reserved for diamond mining. Geologists noticed this structure in the 1960s, and meteoritic origin was proposed already in 1965 (1). Few people entered this remote part of Namib Desert – only in 1986 and 1987 further research took place and the impact origin of the Roter Kamm crater was confirmed.

Researchers in the 1990s proposed that this meteorite fell approximately 3.7 million years ago. More recent research from 2008 shows different results (2) – laser argon dating shows that the impact took place some 4 – 5 million years ago, in Pliocene.

Geology

Diameter of this crater is 2.5 km and depth (height difference between the highest part of its rim and deepest part of central part) – 130 m. Rims of the crater rise some 40 – 90 m above the surrounding plain but the interior is located some 50 m below the surrounding plain.

It is estimated that the crater is filled with at least a 100 m thick layer of sand. Only in some sectors in the ridges is exposed bedrock. Roter Kamm crater is degraded but nevertheless, it is one of the best visible impact craters on Earth.

Meteorite here hit very old (Precambrian, 1.2 billion years) granitic gneiss – Namaqua Metamorphic Complex with some younger sedimentary rocks. There have been found no pieces of meteorite – most likely it has evaporated totally during the impact. Melted rocks contain traces of this chondritic meteorite.

Most ejecta is found to the northwest – west from the crater. This and the oblong shape of crater suggest that meteorite was falling from south-east.

References

1. Dietz R. S., 1965. Roter Kamm, Southwest Africa – probable meteorite crater: Meteoritics, v.2.no.4.p.311 – 314.
2. Lutz Hecht, Wolf Uwe Reimold, Sarah Sherlock, Roald Tagle, Christian Koeberl, Ralf-Thomas Schmitt. New impact-melt rock from the Roter Kamm impact structure, Namibia: Further constraints on impact age, melt rock chemistry, and projectile composition. Meteoritics & Planetary Science. Volume 43, Issue 7, pages 1201–1218, July 2008.

Roter Kamm crater is included in the following articles:

This comparison with Meteor Crater is a matter of taste – the Pingualuit crater in Canada or Lonar crater in India are magnificent natural landmarks as well, several more craters (e.g. in Algeria and Mauritania) are very impressive as well. Nonetheless Wolfe Creek crater is highly unusual, magnificent natural landmark.

Aboriginal legends

This crater – Kandimalal – was well known to local Djaru people and is the centerpiece of several local legends. Local people even considered that it has been created by a fallen star, the legend seems to tell a story about real meteorite impact!

According to this legend once upon a time a crescent moon and evening star passed each other too close. The evening star became too hot due to this and fell to the ground.

As the star hit the ground, there was great explosion, flash and giant cloud of dust.

Another legend tells that the rainbow snake named Kalpurtu came out from the underground through the crater (another rainbow snake meanwhile created the nearby Sturt Creek). According to legend sometimes a bright light shines from the crater, also the giant snake can be seen sometimes.

Aboriginal art of this region often depicts the crater and rainbow snake.

Discovery by scientists

Crater was noticed from the air by geologists Frank Reeves, N.B.Sauve and pilot Dudley Hart on June 21, 1947. Two months later they reached the crater on the ground.

Frank Reeves named the crater after the adjacent Wolfe Creek, which in turn was named after Robert Wolfe – local prospector and storekeeper during the gold rush.

Size of crater

Average diameter (from rim to rim) of this crater is 875 m. Rims of crater rise 25 – 35 m above the surroundings. Present depth of crater is up to 60 m below the rims and up to 25 m below the surroundings.

Rims of crater are up to 40 degrees steep.

In the central part of crater is located a white area with sediments of gypsum – traces of ephemeral lakes which appear after the rare summer rains.

Conditions for life inside the crater are more beneficial due to porous ground, presence of water and shade. Here grow even some larger trees and many other plants, animals here are met more often than elsewhere.

Impact

Crater was created by more than 50 000 tonnes heavy meteorite less than 300 000 years ago.

This meteorite fell with the fantastic speed – approximately 15 km per second. Meteorite exploded when it hit the laterites and 700 – 800 million years old Precambrian quartzite.

The powerful explosion melted the rock and scattered impressive blocks of red-brown quartzite and pieces of meteorite around the crater.

Initial depth of crater was some 120 – 150 m. Later it was partly filled with sand and gypsum.

Medium octahedrite

This impact was caused by a meteorite consisting of iron and nickel – medium octahedrite (IIIAD meteorite).

Crater and its vicinities (even 3.9 km far from the crater) contain many pieces of meteoritic mass. Some pieces have been well preserved, others have turned into "shale-balls" – up to 250 kg heavy clusters of balls from iron oxide.

Two previously unknown, very rare minerals have been discovered in this site – reevesite (named after Frank Reeves) and cassidyite (named after William A. Cassidy who mapped the crater).

Wolfe Creek crater is the second largest crater in the world (after Meteor crater in Arizona) where peaces of meteorite have been found. Generally in larger explosions the meteorite evaporates.

References

1. Outback Australia – travel guide. Wolfe Creek Meteorite Crater National Park. Accessed on January 16, 2013.

Wolfe Creek crater is included in the following articles:

This is one of the best-preserved impact craters on Earth, a truly unique place where one can learn, what happens when Earth is bombarded by a meteorite.

Description

Meteor crater is located in a desert with scarce vegetation cover. It is very impressive. Rims of the crater are visible from far away and rise up to 45 m above the surrounding plains.

When one reaches the rim, there opens a grand view on approximately 1,200 m wide, up to 170 m deep crater. The crater is not entirely round but rather square, which, possibly, is caused by joints in bedrock.

The impact

50,000 years ago the climate in Arizona was more temperate than now. This was the ice age – further, in the north, there were giant glaciers, but there were growing forests, walking large Pleistocene mammals – mammoths, ground sloths, and other animals. Most likely this place was devoid of people – they came later.

Impact was almost as fast as lightning.

Some 300 000 tons heavy, 50 m wide iron-nickel meteorite hit the ground with a speed of 12.8 km per second.

Meteorite lost approximately half of its mass before hitting the ground – and the remaining part exploded and evaporated when it blasted in the ground. Most of the metal mixed with the blasted rocks.

The force of the impact was approximately 2.5 megatons – 150 times more than the atomic bomb in Hiroshima. Countless animals and plants died immediately, whole plain turned into a lifeless desert.

Meteorite pierced Triassic and Permian sediments – mudstone, dolomite, limestone, sandstone. Depth of crater reached some 400 meters, surroundings of crater were covered with upturned rocks. The total mass of uplifted sediments was 175 million tons.

Nature heals itself fast. Soon after the crater was filled with a deep lake. Forest returned, the area was full of life again.

210 – 240 m thick layer of sediments formed on the bed of the lake.

As the climate changed, the lake and forest disappeared, desert environment evolved. This helped to preserve the crater and now Meteor crater is one of the best-preserved impact craters on Earth.

History

Meteorite or volcano?

The area around the crater was a well-known location to look for pieces of oxidized iron. It is assessed that some 30 tons of raw iron were found here. The largest known piece is Holsinger meteorite – a 639 kg heavy, 0.9 m long piece, which was found some 2.5 km north from the crater rim in 1911.

Nevertheless the idea that meteorites can create a large crater was something new for science.

In 1891 chief geologist of US Geological Service Grove Karl Gilbert considered that this crater is created either by the explosion of volcanic gas or by a meteorite.

He thought that meteorite should have a similar size to the size of the crater – and that this giant mass of iron should be buried under the crater. Magnetic measurements did not show any significant mass of iron below the crater – thus he concluded that this is an explosion crater caused by volcanic processes.

This hypothesis was widely accepted by the scientific community.

Barringer

When the enterprising lawyer and mine owner Daniel Moreau Barringer (1860 – 1929) learned about the existence of the giant crater in Arizona and pieces of metal found at it, he was convinced that this is a meteorite crater.

He became obsessed with this crater and saw many possibilities in it. If the size of meteorite would be comparable to the size of the crater, here could lie 10,000,000 tons of iron – enough to make its finder one of the richest people in the world.

It was also irritating for Barringer to see that scientists blindly disregard many proofs of meteorite impact and support the hypothesis of volcanic explosion without any direct proof.

Barringer purchased the land (beforehand managing to obtain the name of the local post office – Meteor. This is the formal reason why the crater is officially called Meteor Crater) and established “Standard Iron Company”.

In 1903 – 1905 there were made first drills that did not bring the desired result. They obtained more and more proofs for meteorite impact – but could not find the giant chunk of iron.

There were made up to 419 m deep drills and Barringer spent most of his fortune and ran in debts. In 1929 he obtained proof that large meteorites are vaporized during the impact event. Shortly afterward he died of a heart stroke.

Some discussions about the origin of this crater continued until the 1960s when Eugene Merle Shoemaker added more proof in favor of the impact hypothesis and profoundly described the crater. Here were discovered two rare forms of silica – coesite and stishovite, which are created by extreme overpressure.

The crater is the property of the Barringer family up to this day. This inhospitable, alien-looking crater has served as a true oasis for the scientific research and popularization of science. There is built Meteor Crater Visitor Center on the north rim – it provides rich information about meteorites around the world, space, and astronomy. Access to the bottom of the crater though is limited to scientists.

References

1. The Barringer Meteorite Crater, official website. Acessed in the 31st December 2012.

Meteor crater is included in the following articles:

Place of power

Local Inuit people knew well about this unusual lake. This eerie, unusually calm place was considered to be a site of extreme power, where one comes to revitalize himself.

The name given to it though is more prosaic. "Pingualuit" could be translated as the site "where the land rises", but this translation could designate also skin blemishes due to cold weather.

Discovery and research

White people learned about this lake rather recently.

It is possible that the first ones to notice it were military pilots who used this unusual, round lake for navigation. In June 1943 was taken the first known aerophotographic image of the crater.

Diamond prospector Frederick W. Chubb learned about this unusual lake and became interested in it. He thought that this might be an extinct volcano and there is a possibility to find diamonds nearby.

He asked for the assistance of an expert – Victor B. Meen from the Royal Ontario Museum. Meen immediately noticed that this looks rather like an impact crater (back then there were known just a few impact craters) and was intrigued enough to organize an expedition to this remote area together with Chubb.

Meen and Chubb managed to reach the crater in 1950. Crater was named – Chubb crater.

In 1951 Meen organized another expedition, researchers with a magnetometer found a magnetic anomaly under the northern rim of the crater. It was believed that a large mass with a high content of metal might be lying below the surface here. Later this proved to be wrong – meteorite evaporated during the explosion.

In 1962 Ken Currie found convincing proof of impact hypothesis: impactites – rocks with characteristic deformations caused by meteorite explosion. Such rocks can even have a melted crust, which is enriched with the vapor of meteorite.

Upon the request of Quebec geographers, crater was renamed in 1968 – "New Quebec crater". Current – and the original local name – "Pingualuit" – was returned in 1999.

Description

Impact crater to a large extent has preserved its original, bowl-shaped form. The width of the Pingualuit crater is 3 440 m, depth – 400 m. Rims of the crater rise up to 160 m above the surrounding tundra. The crater rim is the highest point in the whole region, 667 m above sea level. Before the glacial ages, rims definitely were higher – glaciers have eroded them.

Crater sits on a bulge – the catastrophic impact has fractured rocks in a wide area and increased their volume.

Impact took place approximately 1.4 million years ago, in the Pleistocene. The meteorite hit more than 2 billion years old, Archaean granodiorite – very hard rock – and almost immediately evaporated in a terrible explosion, which melted thousands of tons of stone and wiped away all life for hundreds of kilometers around the crater.

Analysis shows that meteorite was chondritic (stone) with siderophile element enrichment (e.g. rich with metals).

Pingualuit Lake

In the crater is located a large lake. The diameter of Pingualuik lake is 2.8 – 3.2 km, depth – 267 m. Rims of crater rise up to 163 m above the lake level and are very steep – 30 – 45 °.

It is dangerous to descend to the lake – there is only one place where one can access the water safely.

Although most of the lakes and rivers in Quebec are incredibly clean, Pingualuk Lake in this respect is in a league of its own. This lake has incredible transparency and contains some of the purest freshwaters in the world, salinity level is less than 3 ppm.

Lake in the right lighting (what is very rare here) has an amazing, incredible blue color. Secchi disk is visible well over 35 m depth – one of the best results in the world. Just a few lakes, like Crater Lake in the USA, Baikal in Russia, and earlier measurements of Lake Mashū in Japan have results above 40 m.

This clarity of the water is explained by several factors. There are no outlets and no significant inlets in this lake. For the most part – from early November to July – the lake is covered with ice. And finally – this is a remote place – the nearest village Kangiqsujuaq is 100 km west of the crater.

In the lake lives Arctic Char (Salvelinus alpinus). The lake environment is very poor and as a result, this isolated population of fish has interesting adaptations – thin bodies and large heads.

Unique geological recordings

Several glacial ages have taken place since the creation of the crater. These glaciers removed all sediments from the bedrock, thus erasing all the information about the past in this part of North America. But there is hope that the bottom of the Pingualuit crater was not affected – this lake most likely survived as a subglacial lake hidden deep under the blanket of the glacier.

An expedition in the winter of 2007 took sediment cores from the deepest place of the lake bed. The total thickness of the sediments here is 11.2 m, but the team managed to get 8.5 m long core.

Research is ongoing, but initial results show the sediments have "recorded" two more interglacial periods before the current one. Remnants of now-extinct diatoms have been found.

Pingualuit National Park

In order to protect the unique impact crater and pristine nature around in 2004 was established Pingualuit National Park.

Crater here is the main attraction. It is not easy to reach it – Pingualuit is accessible by feet, canoe, or by air.

Climate here is harsh – mean yearly temperature is − 10 °C, frost-free season lasts only 20 days.

Crater rim looks like a hill already from the distance of some ten kilometers. Walk towards the rim is tiresome, slopes are covered with rubble and granite boulders.

View to the lake opens suddenly – but what a view! This sight might have no analogs in the world. The lake lies far below and looks closer than it is in reality. Towards the other side opens a view of primeval, endless tundra.

The quietness of this place can be stunning. People can easily hear the small waves of the lake beating against the shores far below.

References

1. Charles O’Dale. Pingualuit impact crater. The Royal Astronomical Society of Canada.
2. Pingualuit crater lake project. Accessed on December 27, 2012.

Pingualuit crater is included in the following articles:

Meteorite or volcano?

Guelb Tenoumer with its perfectly circular form is well known to local people and also Europeans since older times. Already in the 1950s scientists started a discussion whether this crater was formed by a volcano or meteorite.

At first the scattered rocks similar to basalt and rhyodacite around the crater created an impression the this is an ancient volcano. Convincing proof in the favour of meteorite impact was discovered in 1970 when key characteristics of outer impact – planar deformation features – were found in the supposed "lava". Since then it is widely accepted that the Tenoumer crater has been created by meteorite impact.

Three meteorites at once or three different events?

Mauritania has several impressive craters, which are aligned approximately on one line – Aouelloul crater, Tenoumer crater and Temimichât-Ghallaman crater. It is tempting to assume that all three craters were created by one single, catastrophic shower of meteorites.

Further investigations though show that this is not true. Aouelloul crater is old – approximately 3.1 million years. Age of Temimichât-Ghallaman crater is not known, there are discussions still, whether this is impact crater. Tenoumer crater is comparatively new – approximately 21,400 years.

Geology

Diameter of this amazingly circular crater is 1.9 km. Rims of the crater rise some 110 m above the bottom of crater. Research though shows, that this crater is filled with approximately 200 – 300 m thick layer of unconsolidated sediments. Thus Tenoumer crater is very impressive structure, even larger than the famous Barringer crater in Arizona, United States.

Meteorite hit very hard rock – this area is formed from approximately 3.5 billion years old Precambrian gneisses and granites (Reguibat shield), which are covered with thin crust of weathered rock. It is hard to comprehend, how powerful should be an explosion which blasts and melts thousands of tons of such hard stone.

Inner slopes of crater are very steep. Around the crater, mainly to the east, northwest and southwest, are scattered blasted pieces of melted rocks. These pieces are up to 20 m long and contain small, fractured glass inclusions, also other deformations of rock grains have been observed.

No pieces of meteorite, even no traces of it in the surrounding rocks have been found thus far.

References

1. Storzer D., Sélo M., Latouche L., and Fabre J., The Age of Tenoumer Crater, Mauritania, Revisited. Lunar and Planetary Science XXXIV (2003). Accessed on December 26, 2012.

Tenoumer crater is included in the following articles:

Discovery

Local people knew about the existence of this unusual place since ancient times. In the rims of the crater are several ancient tombs. Locals call this place – "hofrath A’welloul" ("Hofrat Aouelloul" – Aouelloul Hole).

First European to see this crater was A. Pourquié, who saw it from an airplane in 1938 while making the aerial photographic mapping of this area. Théodore Andre Monod (Natural History Museum of Paris) reached the site on foot in 1950 and both published account of their discovery in 1951 (1.).

Morphology

Crater has well-defined rims, which rise 15 – 20 m high above the surrounding plains. The diameter of the crater is approximately 390 m – this is a comparatively small impact crater.

The bottom of the crater is up to 53 m below the rims. Sometimes a small, perennial pool of water forms in it – this means that meteorite has not cracked the bedrock.

Geology

Meteorite here met Ordovician sandstone and quartzite rock. The porous mass of sandstone softened the impact, but nevertheless, the consequences were significant. The explosion raised thousands of tons of sandstone and quartzite rock, some of it melted. Now the rim of the crater is formed from a coarse rock thrown up from the crater, part of sand is vitrified by the extreme heat.

The bottom of the crater is covered with a thick layer of aeolic sand and silt. There have been no explorations but it is assessed that the thickness of this layer is approximately 23 m – thus the depth of the crater is up to 56 m without counting the rim or roughly 76 m if the height of the rim is added.

Tectites – main source of information about the meteorite

Only one piece of the meteorite has been found near the crater and it is even not clear whether this piece is from the same meteorite which formed the crater. This stone – Zerga meteorite – was found in 1973.

To the south, south-east, and north from the crater though are found unsightly, semi-transparent, brown stones – tektites. Tectite is natural glass, formed by the heat and scattered by the impact.

Tectites provided valuable information about the Aouelloul meteorite. Analysis of their chemical composition shows that the content of osmium, iridium, and nickel in this glass exceeds the content of these elements in surrounding rocks. Thus it was proved that the Aouelloul crater is an impact crater. The analysis provided also data about the age of meteorite – it is 3.1 ± 0.3 million years, Pliocene period.

This meteorite most likely was chondrite, e.g. it was a stone meteorite, albeit with a rather high content of iron.

It is hard to tell the direction of the impact, but a bit to the north is found another, smaller crater, possibly formed by a smaller piece of this same meteorite. This impact crater shows that the main impact was in the center, e.g. meteorite struck from above.

Very rough calculations show that, if the meteorite approached Earth with a speed of 20 – 25 km per second, this meteorite had a diameter of some 20 m.

Meteorite seekers

Sometimes (elsewhere) tektites are beautiful gemstones, but the main value of tektites is their rarity, these are valuable items for collectors.

The desert near Adrar is almost lifeless and the red hue of sand makes it similar to Mars. Heat here for most time is almost unbearable and Europeans, who search for tektites, soon conclude that the outcome is not worth the effort.

Most tektites are found by boys – shepherds, who sell them to merchants. These stones rarely exceed the size of a fist.

In local markets most tektites are falsifications. The few tourists coming to this area often are buying just a slag from old iron smelters and even stones processed by people in Neolithic Age.

Crater is privately owned, visitors are asked to leave cars outside the crater and not to make tents inside it.

References

1. Th. Monod, A. Pourquié. Le crateré d’Aouelloul (Adrar, Sahara occidental). Bulletin de l’Institut fondamental d’Afrique noire, 1951, 13, p.293 – 311. Accessed on December 26, 2012.
2. Cosmic Secrets. The Enigmas on Earth – Impact Craters on Earth. Accessed on December 26, 2012.
3. Christian Koeberl, Wolf Uwe Reimold, Steven B. Shirey. The Aouelloul crater, Mauritania: On the problem of confirming the impact origin of a small crater. Meteoritics & Planetary Science 33, 513-517 (1998). Accessed on December 26, 2012.

Aouelloul crater is included in the following articles:

Volcanic crater, sinkhole or… impact crater?

The unusual, round lake in the central part of Saaremaa was well known to local people. Initially scientists thought that this is volcanic crater or sinkhole, formed by a collapse of large cave.

Geologist Ivan Reinvald (1878 – 1941) was sent to explore this natural feature in 1927. He was not sure at all that this is a sinkhole or volcanic crater – Reinvald considered that it was formed by a meteorite. In 1935 he found small pieces of a meteorite but in 1937 – two smaller craters nearby. Thus it was proved that Kaali Crater is formed by meteorite.

Today Kaali Crater is recognized as one of the most outstanding geological landmarks in Estonia. There has been established a specially protected area (50 ha), near the crater, has been constructed a visitor center.

Attack from the space

This crater is like a large scar amidst the idyllic rural landscape of Saaremaa and tells about the terrible events which happened here in Bronze Age.

Different methods of dating show different results – but currently most specialists agree that catastroph happened more than 4 000 years ago, possibly – 7 600 years ago, at 5 600 BC. Most likely Saaremaa and surrounding lands were inhabited in these times.

The everyday life of those people changed (or ceased) dramatically in a fraction of second.

Some 400 – 1 000 tons heavy meteor entered the atmosphere of Earth with a speed of 15 – 45 km/s. It was not like meteors of action movies, which seem to be as slow as airplanes before landing. This real meteor would seem lightning fast to human eye.

Atmosphere almost immediately heated this stone mass, it started to slow down and evaporate. At the height of some 5 – 10 km metor divided into smaller pieces and after a fraction of second these pieces hit the central part of Saaremaa from the north-east, at the angle of 45° and with a speed of 10 – 20 km/s. It was like a giant bullet with a diameter of some meters but: some 10 – 25 times faster than bullet!

The largest piece, which created Kaali Crater, was approximately 20 – 80 tons heavy.

The effect of this cataclysm could be compared to the effect of the nuclear blast.

Geological consequences

Overheated meteorite penetrated the dolomite layers and exploded. The giant mass of meteorite was vaporized – the largest piece found thus far does not reach 40 grams. Small pieces of meteorite can be found now in Saaremaa, Muhu island, and Western Estonia, glassy spherules have been found in the bogs of Western Estonia, in a layer which formed some 7,600 BC.

The force of the largest meteorite fractured the Silurian dolomite into small pieces up to the depth of 40 – 50 meters. Some 110 m wide and approximately 25 m deep crater was formed, with a 3 – 7 m high rim of debris around it. Approximately 81 000 m³ of dolomite were ejected from the crater, forming some 7 – 8 km high, extremely hot gas flow.

Other pieces of meteorite formed smaller craters, with 12 – 40 m diameter, 1 – 4 m deep. Thus far have been found nine craters, all within a distance of 1 km from the main crater. Most likely there were many smaller craters, but these have disappeared now.

Saaremaa and nearby areas experienced significant earthquakes but extreme heat scorched everything in a distance of some 6 kilometers.

Today Kaali Crater has a lake in it – this lake has a diameter of 30 – 60 m and depth of 1 – 6 m, depending on the time of year. Lake is fed by groundwater and precipitation. The crater is 16 m deep now (not counting the rims of debris), the lake has up to 6 m thick sediments. Upturned blocks of dolomite can be seen in the walls of the crater.

Historical consequences

Most likely people died in this unexpected catastrophe. The life of survivors was never the same again – we can only try to imagine how the prehistoric people were constantly waiting for the next terrible hit from the sky. Such catastrophes cannot be easily forgotten, people remembered these events for many generations and gradually these historical events turned into mythological events.

The crater and its surroundings were unbearably hot initially. Gradually it cooled down but this scar of Earth most likely was taboo to local people for some centuries. Kaali Crater got a very special status – it became a cult site.

In the early Iron Age there was built a dry stone wall around the crater. This wall was 470 m long, approximately 2 m high. It is well possible that it concealed some covert activities from the common people, although the purpose of this wall is not entirely clear.

In the sediments of Kaali Lake has been found a silver collar and bracelet from around the 3rd – 5th century AD. Many bones of domesticated animals have been found as well – animals were sacrificed here even in the 17th century. Further research in the sediments of Kaali Lake could bring more discoveries.

Estonian, Finnish and Scandinavian folklore includes some tales, which could be linked to this prehistoric event. It is possible that even Greek folklore tells about it: the story of Phaeton – the son of Sun god Helios could be based on the narrative about this cataclysm.

References

1. The Kaali meteorite craters. Saaremaa, Island of Baltic Sea. Accessed in the 22nd November 2012.
2. Anto Raukas, Kustav-Olimar Laigna. Height of the turbulent gas flow and transport distance of glassy spherules on the example of the Kaali impact, Estonia. Proceedings of the Estonian Academy of Sciences. Geology. September 2005.

Kaali Crater is included in the following articles: