Re: A 37 million year old lake?
- From: Aidan Karley <doIlookDAFTenoughTOpost@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 07 Jun 2006 12:35:12 +0100
In article <e65mkn$hfr$1@xxxxxxxxxxxxxxxxx>, Paul Ciszek wrote:
According to Wikipedia, http://en.wikipedia.org/wiki/Lake_WanapiteiSatellite photo at
the impact that created Lake Wanapitei occured 37 million years
ago. Now, it may not have been a lake that whole time, but
whatever depression the impact created has had 37 million years
to fill in. And it probably *was* a lake for much of that time,
any time it was below the local water table. Why is it still
concave?
http://maps.google.com/maps?t=k&hl=en&om=1&ll=46.75,-80.75&spn=0.28576,
0.635834
As you say, it probably *was* a lake for much of the time since
impact. But for most of the last couple of million years it's been a
some-what shattered area of rock underneath a glacier. The glacier has
been slowly grinding out the rock, but doing it (slightly) more rapidly
than the surrounding rock. So the depression has been recreated - and
probably most of the lake deposits have been dug out.
In the last few millennia that the ice has been gone, material
has been washed in to the lake from several streams etc. The NW corner
appears to have a nice little delta-shaped delta in it.
Compare the Nordlingen Ries crater. That's about 14 million
years old, but wasn't over-ridden by the glaciation, so it still
retains it's fill of lake sediments etc.
http://maps.google.com/maps?t=h&hl=en&om=1&ll=48.890004,10.546875&spn=0
286685,0.635834
shows the area, and the (relatively) good farm land of the lake
deposits stands out well against the more wooded surrounds and the rim
of crater wall deposits.
--
Aidan Karley, FGS
Aberdeen, Scotland
Written at Wed, 07 Jun 2006 12:09 +0100, but posted later.
.
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- A 37 million year old lake?
- From: Paul Ciszek
- A 37 million year old lake?
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