[meteorite-list] Terrestrial Impact Craters

From: Jensan Scientifics/ Sci-Mall <jensan_at_meteoritecentral.com>
Date: Thu Apr 22 09:52:10 2004
Message-ID: <3D55CECC.A4295507_at_pcii.net>

Hello Keith, hello Tracy,

Tracy is correct in her appreciation of crater-wiping forces on Earth.
There are very few terrestrial impact sites of great age (Barringer is a
youngster at abt. 50,000 yrs) that remain without plenty of alteration!

Here are two items to add to the discussion, though...

The Wabar impact, although not that large, occurred in sand and several
craters remain visible. They have retained shape in part due to the
formation of a glass lining in the crater bowl that resists wind
erosion. They may fill and empty over the years as the surface dunes
shift.

The so-called "splosh" craters on Mars have very obvious lobate ejecta
blankets that suggest the impacts occurred in a wet target material. For
a neat simulation of this, consider the way the Yellowstone mudpots toss
gooey mud into an ejecta pattern as the bubbles burst at the surface.
The difference on Mars is that, unlike the mudpots model, the ejecta
remains frozen in shape on the surface for us to see today after many
millenia.

You can see lots of crater comparison info on the newly published
poster:

"Meteorite Impact Craters on the Earth"......at..

http://www.sciencemall-usa.com/impactposter.html

Best,
Dave and Sarah
.................................
.................................

Tracy Latimer wrote:
>
> I think that any crater in loose sediments would likely be filled in
> rapidly by the same mechanisms that deposited the sediment in the first
> place. You might, for a while, be able to track the crater by deformation
> in the surrounding sedimentary layers, but eventually it would all even
> out, leaving barely a ruffle in the geologic record. Only craters in
> hard, non-disappearing rock, not sludgy mud, would have a chance of
> remaining long enough for us to discover them.
>
> Tracy Latimer
Received on Sat 10 Aug 2002 10:41:16 PM PDT