Drilling For Africa's Climate History

[zavvy]

<b>Drilling For Africa's Climate History</b><br /><br />LINK<br /><br />The still waters of Lake Bosumtwi impose a sense of deep calm on those who visit the sub-Saharan African nation of Ghana. But the silence, punctuated by occasional frogs' croaks and bird calls, belies a violent origin.<br /> <br />"A million years ago, this was the site of an enormous catastrophe," explains Christian Koeberl, a geologist from Vienna University, Austria. <br /><br />"We had a lush rainforest, filled with animals minding their own business, when a kilometre-sized rock came hurtling down from space, at enormous velocity, and crashed into the ground here. <br /><br />"Within a few seconds, it opened up a gigantic hole in the ground which later filled with water and became the lake we see today," he told the BBC World Service's Discovery programme. <br /><br />Researchers know of 170 impact craters around the world, including the enormous Chicxulub structure in the Gulf of Mexico formed 65 million years ago, and widely associated with the demise of the dinosaurs. <br /><br />But Lake Bosumtwi is unique to science, says Professor Koeberl. <br /><br />"It is the youngest large impact crater we have on Earth, and it's very well preserved. There is no crater of the same size that is younger; and there is no crater that is better exposed or larger." <br /><br />Earth prepared <br /><br />This summer, following a 10-year campaign of geological field work and geophysical investigations, Koeberl and a team of collaborators brought a floating drilling platform, to bring up samples of crushed and melted rock from the basement of the crater. <br /><br />"What we're trying to understand is how exactly the meteorite hit the Earth, from which direction did it come, what type of meteorite it was, and what were the immediate consequences," Professor Koeberl says. <br /><br />"There are many more rocks of this size out in space - and an impact

 

[thalion]

For a climate geek like myself, this is a great article. Thanks for posting it!

 

[meteo]

Crater and tectonic lakes are great because they are deep (no oxygen at the bottom, critters don't stir up the mud) wave action also doesn't penetrate to the bottom. Lake Bosumtwi is the deepest lake in Ghana. The accumulation is usually slow and steady. However, since the accumulation is so slow these lakes have "low resolution." The low accumulation of sediment is also good if you want to go far back into time. Slow accumulation means it takes a while for the lake to fill up with sediment (with no drainage).<br /><br />Feeling adventerous check out "Paleolimnology: The History and Evolution of Lake Systems" everything you ever wanted to know about lake evolution. <br /><br />Yes, I am also a climate geek. <img src="/images/icons/smile.gif" />

 

[diogenes]

Aren't those the kinds of lake that sometimes wipe out their surrounding environment?<br /><br />I'm thinking like Nyos and Monoun.<br /><br />http://perso.wanadoo.fr/mhalb/nyos/nyos.htm

 

[meteo]

No, sorry; the tectonic lakes I'm referring to are just lakes that happen to be very big and very deep.<br /><br />Lake Tanganyika<br />Nyasa Malawi<br /><br />By tectonic lakes I'm noy refferring to hydrothermaly active lakes, but rift lakes. They are usefull because of the slow steady accumulation over long periods of time. A glacial lake that was as deep would be just as usefull. It just happens that becuase of the way lakes are formed tectonic lakes are the deepest.<br /><br />The size of these lakes tends to smooth out the local variance becasue they are so big (the temperature at the bottom of these lakes changes over longer periods of time then a small pond), so large lakes are usefull for a global perspective but for a local climate perspective it is better to select a smaller more sensitive lake (a smaller crater lake.)