The known impact structures on Earth are far behind the total presumably preserved on the land. There is therefor plenty of possibilities for finding new impact craters. Having found a possible candidate the big work begin - to prove that it is indeed caused by an extraterrestrial impact.
A new ring structure found in Central Africa (revealed by deforestation) could be one of the larger impact crater discovered in the last decade and one of the largest ever according to findings presented the Lunar and Planetary Science Conference in Texas, US, March 2010.
The ring structure is located in the Eastern Kasai province (R.D. Congo) and is centered at 3??37'50''S, 24??31'00''E, 37 km north of Wembo-Nyama. It is recognisable from satellite images for the perfect roundness of the ring. If the external rim of the thalweg is taken into account, the annulus has a total diameter of 36 km. The central part of the structure is irregular and about 50-60 m higher than the depression where the river flows.
The stratigraphy of the area, where the structure occurs, consists of a Precambrian Basement covered by the Karoo Supergroup of late Palaeozoic ' Triassic age (~800 m thick), in turn overlaid by a Jurassic-Cretaceous sedimentary succession. The whole succession is characterized by continental deposits (sandstones to clay, tillite and conglomerates) and is buried by Plio-Pleistocene fluvial and colluvial deposits. The topography indicates a diameter of the structure from 36 to 46 km, but the outer ridge is not well developed, likely deeply weathered and eroded by tropic climate.
The stratigraphy does not match a saltdiapir origin of the ring.
The diameter is too large for a kimberlitic pipe.
A caldera structure is excluded.
A batolith is unlikely.
The authors conclude that an impact origin may be the more valuable solution, and their guess is that it was caused by a major impact event that happened during Cretaceous-Cenozoic time span.
The team will now have to travel to the region to carry out field studies, and examine rocks from the site for tell-tale signs associated with extraterrestrial impacts. Further studies will also be required to accurately determine an age for the ring, but it appears to post-date the Jurassic Period (younger than 150 million years).
Reference:
The Ring Structure of Wembo-Nyama (Eastern Kasai, R.D. Congo): A Possible Impact Crater in Central Africa G. Monegato, M. Massironi, E. Martellato
41st Lunar and Planetary Science Conference (2010), Abstract #1601
Areas of hypoxia, or low oxygen, have long existed in the deep ocean. These areas ' in the Pacific, Atlantic and Indian oceans ' appear to be spreading, however, covering more km??, creeping toward the surface and in some places, such as the US Pacific Northwest, encroaching on the continental shelf within sight of the coastline. In some spots off Washington state and Oregon, the almost complete absence of oxygen has left piles of crab carcasses littering the ocean floor, killed off 25-year-old sea stars, crippled colonies of sea anemones and produced mats of potentially noxious bacteria that thrive in such conditions. Off the Southern California coast, oxygen levels have dropped roughly 20% over the past 25 years.
Commonly, ocean "dead zones" have been linked to agricultural runoff (nitrate loads) and other pollution coming down major rivers such as the Mississippi or the Columbia. One of the largest of the 400 or so ocean dead zones is in the Gulf of Mexico, near the mouth of the Mississippi. However, some of these areas, including those off the Northwest, are apparently linked to broader changes in ocean oxygen levels due to global warming.
1) Northerly winds drive surface water away from shore
2) Oxygen-poor water sucked to surface through upwelling
3) Deep water rich in nutrients fertilises phytoplankton (plankton bloom)
4) Phytoplankton sink to bottom and decay, using plenty of oxygen
During the summer, northerly winds aided by the Earth's rotation (coriolis force and Ekman transport) drive surface water away from the shore. This action sucks oxygen-poor water to the surface in a process called upwelling. Though the water that is pulled up from the depths is poor in oxygen, it is rich in nutrients, which fertilize phytoplankton. These microscopic organisms form the bottom of one of the richest ocean food chains in the world. As they die, however, they sink and start to decay. The decaying process uses oxygen, which depletes the oxygen levels even more.
A few days ago Turkey was struck by a strong earthquake at the East Anatolian fault. As you could see on the USGS tectonic map that I showed in my post on that occasion, the Anatolian block is bounded on the southeast by the East Anatolian fault and the north by the North Anatolian fault. The Anatolian block is moving west relative to the advancing Arabian plate at a rate of about 24 millimeters a year.
The North Anatolian Fault has often been in the news because of earthquakes. It is a 1,500-kilometer-long east-west trending fault that runs across most of Turkey. Since 1939, a progression of deadly earthquakes has been marching westward across the fault - westward towards Istanbul where there is now a seismic gap. A seismic gap is a segment of an active fault that has not slipped in an unusually long time when compared with other segments along the same structure, and people surviving the disastrous earthquake in Chile on Saturday 27 February 2010 will know what that means. In Turkey Istanbul is the next likely target. A new study, however, suggests Turkey's largest city may be struck by a series of moderate earthquakes, rather than one big event.
Slip rates for the North Anatolian Fault have previously been reported as anywhere between 12 and 28 millimeters per year. Only the main branch of the North Anatolian Fault were so far taken into account. The new study included many of the smaller fault strands that have only recently been mapped. The new models, published in Nature Geoscience, indicate that the smaller faults are actually accommodating much of the fault's movement. The North Anatolian Fault is therefore only slipping by between 12 and 17 millimeters per year - according to Hergert & Heidbach.
Even a moderate event of a magnitude of 7.0 could, however, do serious damage to Istanbul, a populous city with many high rises and somewhat lax building codes. Whether Istanbul is struck by a magnitude 7 or 7.6, the damage is likely to be substantial.
Let's face it. There has been no big increase in the number of magnitude 6.0 earthquakes in the past decade - and not in magnitude 7.0 earthquakes either.
Todays earthquake in turkey was magnitude 5.9. According to USGS data, the world is hit by about 134 earthquakes a year in the 6.0- to 6.9-magnitude range ' or about two a week. Earthquakes are common and always have been.
That we have seen such a large death toll over the last couple of months is coincidence, and part of a natural variability. The Haiti quake struck in a very unfortunate place.
Increased construction up and down the world's fault lines like the East Anatolian fault in Turkey is certainly not due to global warming, or a full moon on Old Year's Night, or your mortal sins. We are just more people on this small earth than we were ten, or 100, years ago. In 2009 alone the human population increased by close to 75 million people, and they have to live somewhere, so more people now live in earthquake prone areas, and that is it!
Apart from that earthquakes (and other natural hazards) also seem to get more attention in the media. If this could lead to better understanding of how earthquakes work, and to higher earthquake preparedness, I would be happy.
You shouldn't call a town Bingo I thought, when I saw a report from USGS on a strong Earthquake in eastern Turkey.
My new glasses are apparently not good enough, as it turned out to be Bing??l - and I apologise to my Turkish friends. It is not the first time that the area of Bing??l has been hit by a strong earthquake. Some will remember the quake there on 8 May 2003, when the whole area suffered from a magnitude 6.4 earthquake, leaving 177 dead and 520 injured. Now on 8 March 2010, the area suffered another earthquake, of magnitude 5.9, with its epicenter 45 km west of Bing??l.
Until 1950, Bing??l was known as ??abakcur (Armenian: ''''''), which means violent water in Armenian. It is surrounded by mountains and a large number of glacier lakes, hence the name, but the underground seems to be violent as well.
The town lies at the East Anatolian Fault, a major geologic fault that runs along the tectonic boundary between the Anatolian Plate and the northward-moving Arabian Plate. The difference in the relative motions of the two plates is manifest in the left lateral motion along the fault.
As the new quake with a magnitude of 5.9 (or 6.0) occurred at approximately the same place as the one in 2003 we can reuse the USGS tectonic map from back then with the earthquake marked as a red star.
Turkey is a tectonically active region that experiences frequent destructive earthquakes. At a large scale, the tectonics of the region near the recent earthquake are controlled by the collision of the Arabian Plate and the Eurasian Plate. At a more detailed level, the tectonics become quite complicated. A large piece of continental crust almost the size of Turkey, called the Anatolian block, is being squeezed to the west. The block is bounded to the north by the North Anatolian Fault and to the south-east by the East Anatolian fault. The recent earthquake occurred near the east end of the East Anatolian fault. The faulting in the region is very complicated and extensive. This earthquake may have been the result of rupture on the northeast trending East Anatolian Fault or it may have occurred on the northwest trending Bingol Karakocan fault zone.
At the time of writing at least 57 people were reported killed by the new earthquake.
Was the whole planet covered by a thick layer of ice 716.5 million years ago? A white planet instead of the present 'blue planet'? The so-called 'snowball earth' events are the subject of much scientific controversy. The main debate involves whether these glaciations were truly global or merely localised events.
Fact is that the cold era known as the Cryogenian (from Greek cryos "cold" and genesis "birth"), and that lasted from 850 to 630 million years ago, was blessed with at least two ice ages far worse than the most recent glaciations in the Pleistocene (2.588 million to 11'700 years BP). The Sturtian (in the Cryogenian, around 716.5 million years ago) and Marinoan glaciations (in the Cryogenian, around 635 million years ago), are the greatest ice ages known to have occurred on Earth. There has been and is disagreement as to just how severe the Sturtian glaciation was.
An important aspect in the discussion is exact dating of the glaciation events. A new study published in Science of 5 March 2010 dates Sturtian glacial deposits at 716.5 million years ago. Based on the estimated past positions of where these rocks were deposited (i.e. about 10 degrees latitude of the equator), glaciers probably extended to equatorial latitudes at that time. The data also seem to suggest that the Sturtian glaciation lasted for at least 5 million years.
The age of 716.5 million years closely matches the age of a large igneous province stretching more than 1,500 km from Alaska to Ellesmere Island in far northeastern Canada. This coincidence could mean the glaciation was either precipitated or terminated by volcanic activity.
The survival of eukaryotic life throughout the Sturtian period indicates sunlight and surface water remained available somewhere on the surface of Earth. The earliest animals arose at roughly the same time, following a major proliferation of eukaryotes.
Even in a snowball Earth there would be temperature gradients on Earth and it is likely that ice would be dynamic: flowing, thinning, and forming local patches of open water, providing refuge for life.
This is not the end of the debate, but a few cool facts can help the discussion forward.
For uninitiated, and of course for those with a short memory, there is an overview of (the history of) the snowball earth hypothesis at the Snowball Earth website.
Reference:
Calibrating the Cryogenian by Macodnald et al.
Science, 5 March 2010.
A German submarine was sunk on 9 February 1945 by a British submarine. The shipwreck was located in March 2003 by the Royal Norwegian Navy some 3.5 km west of the island of Fedje in the North Sea, at a depth of 150 metres.
It is now forbidden to fish in the vicinity of the wreck, which contains around 67 tons of mercury. Fish with a higher concentration of mercury have already been caught in the area. The danger is that the poison could eventually pass up the food chain, and be ingested by humans.
It was first decided to entomb the wreck, which also is supposed still to contain dangerous torpedoes, but later the Norwegian authorities changed their mind, as the proposal of entombing the wreck rather than removing it was criticised by locals concerned about possible future leakage. On 29 January 2009, the Norwegian government approved a proposed method of raising the wreck, and the operation was scheduled to begin in 2010. The project has however been postponed a couple of times, not so much because of lack of funds (the operation was originally estimated to cost around 1 billion Norwegian kroner = 125 million ', but is now re-estimated to about the double of this amount), but due to remaining safety concerns.
The earliest possible date is now some time in 2012 - and the mercury cargo is still leaking (3 kg per year?)
I have often written about extraterrestrial bodies, like meteorites, forming craters when they collide with our Earth. Sometimes however they explode in the atmosphere before reaching the surface of the Earth. Such space rock explosions are known as "airburst".
This is what probably happened at Tunguska on 30 June 1908. The blast flattened some 2,000 km?? of Siberian forest, knocking people to the ground about 60 km from the epicentre.
Airbursts on the scale of the Tunguska event are thought to occur every 500-1,000 years on Earth. This figure is based on computer modelling by Dr Bland and his colleagues.
According to new research presented at the 41st Lunar and Planetary Science Conference a large space rock may have exploded over Antarctica about 481,000 years ago, showering a large area with debris. The evidence comes from accumulations of tiny meteoritic particles and a layer of extraterrestrial dust found in Antarctic ice cores.
The debris includes micrometeorites and aggregates of microscopic spherules, like the aggregate shown in the SEM-BSE (microanalytical Scanning Electron Microscope) image above. Some of the debris in question is found more than 2,900 km apart. For cosmic debris to be spread over such a wide area, Ginneken et al. propose that an airburst is the most likely explanation, and they estimate that it could have been caused by an object weighing 100,000 tonnes.
The work may show a way of spotting other 'airburst' events in the geological record.
The Ugandan slopes of Mount Elgon is a densely populated mountainous area where landslides have been reported since the beginning of the twentieth century. Besides the fact that steep slopes, high rainfall and typical soil properties and stratification turn the area into an inherently unstable area, human interference play an important role. Deforestation has reduced the stability of the shallow soils on the eastern slopes, and the excavation of slopes, mainly for house building, is an important destabilizing factor for the western slopes. The growing population density not only increases the risk on damage, but hampers the search for solutions for the landslide problem as well.
In 2007, heavy rains that humanitarian officials said were the worst for 35 years battered eastern Uganda, forcing 2,000 people from their homes and affecting 50,000. Although the region is prone to landslides, the death toll has rarely been so high as now.
Following a heavy downpour in Nametsi village on the slopes on Mt Elgon in eastern Uganda on Monday 1 March 2010, massive landslides struck the Bududa District and the neighboring districts of Sironko and Bukwaon Monday night. They wiped out several villages around Mount Elgon and more than 100 bodies have since been recovered. Yesterday an estimated 245 people were still missing and feared dead in the Bududa district, while death toll and damage in the neighbouring districts were still unknown.
Mount Elgon, the second-highest mountain in Uganda, is an extinct shield volcano 4,321 metres high. It is located about 350 km east of the capital, Kampala. It is the oldest and largest solitary volcano in East Africa, covering an area of around 3500 km??.
Mount Elgon (red marker) at 1.133 N, 34.55 E - just west of the Great Rift Valley
NASA Earth Observatory has published a nice satellite image of the Acraman impact structure in South Australia. The Acraman crater is a so-called complex crater, as opposed to simple craters - see drawing below:
The intermediate crater ring and the (possible) outer crater ring are indicated by dotted white lines.
The impact event is estimated to have occurred about 580-590 million years ago. This age is not derived from the crater itself but from the position of ejecta within nearby sedimentary basins. A remnant of the impact is Lake Acraman, seen in the middle, a small, circular, shallow salt lake about 20 km in diameter.
The evidence for impact includes the presence of shatter cones and shocked quartz in shattered bedrock on islands within Lake Acraman.
Geological studies have found that, over time, Acraman's surface eroded several km below the original crater floor. Studies of the current land surface and debris ejected by the collision suggest that the impact produced an uplifted ring spanning roughly 40 km in the crater's center. The rim surrounding the inner ring may have spanned 85 to 90 km, and the total area of disturbed rocks might have been as wide as 150 km.
Radiometric dating of the rocks affected by the Acraman impact indicates that the event occurred almost 600 million years ago, during a geologic period known as the Ediacaran (sometimes called the Vendian). Although our planet was more than 4 billion years old at that time, it was still before the time when life forms began leaving behind a rich fossil record. Nevertheless, fossils do occur in Ediacaran rock layers, and many of them are acritarchs'small (often microscopic) fossils that could result from a wide range of organisms.
A dramatic change in the types of acritarchs found in the Ediacaran rock record coincides with the estimated occurrence of the Acraman impact. Although some studies have linked this fossil turnover to a nearly worldwide glaciation ('snowball earth'), others have suggested the Acraman impact as a possible cause of the widespread disturbance to life on Earth at that time.
The discovery of the crater and independent discovery of its ejecta were first reported in the journal Science in 1986.
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