I seriously doubt that any crater on Earth was caused by impact. In another thread I mentioned Kebira Crater, which was most likely the cause of the fragments of glass that are scattered in the Great Sand Sea near Gilf Kebir. The glass chunks are incredibly pure -- so much so that Egyptologist who found a piece in King Tut's tomb wrote that such purity was impossible for modern glass-makers, so how did the ancients do it?
The answer is that the glass was not man made, but was formed by fusing the silica sands at incredible temperatures. If the glass had been created by impact, then it would be contaminated by halite and alumina, the predominant minerals in the area, but it is as clear as water. The interesting feature about the "desert glass" is that dark swirls of pure iridium are emdedded within in. Tiny bubbles of cristabolite, a mineral that is formed at extremely high temeratures, are also there. How?
The so-called K/T boundary layer contains spherules of glass that are high in iridium -- they might have come from Popigai Crater, or from Chesapeake Bay. Currently, those two formations are the probable sources for the glass beads. In Bass River, New Jersey are thick layers of glass spherules just off the coast at almost a thousand meters depth. They are also clear as glass.
Here's a tip that Lloyd originally gave me about searching this site for information. If you want to find articles about a particular topic type in Google, site:thunderbolts.info "search term"
Putting "crater" as the search term returned these results (abbreviated list):
Richat Crater Revisited (2) Aug 12, 2005 ... Why, for these craters, is it so difficult to find evidence of impact that cannot also be explained by electrical discharge, ...http://www.thunderbolts.info/tpod/2005/ ... visit2.htm
- 13k - Cached - Similar pages
Aorounga Crater May 3, 2006 ... Satellite radar images of the Sahara desert north of Chad have revealed the presence of craters not easily noticed in normal aerial ...http://www.thunderbolts.info/tpod/2006/ ... crater.htm
- 14k - Cached - Similar pages
Popigai Crater, Siberia Jan 7, 2008 ... The infamous Tunguska crater is not the only site in Siberia where tremendous high-energy events have taken place.http://www.thunderbolts.info/tpod/2008/ ... crater.htm
- 19k - Cached - Similar pages
Richat Crater Revisited Aug 11, 2005 ... Why do these three craters and a fourth line up and why are they so circular?http://www.thunderbolts.info/tpod/2005/ ... evisit.htm
- 10k - Cached - Similar pages
Manicouagan: Impact Crater or Lightning Scar? Nov 26, 2007 ... A giant ring-shaped crater in Canada seems to be the result of a meteor strike. Could electrical scarring be a better explanation?http://www.thunderbolts.info/tpod/2007/ ... ouagan.htm
- 19k - Cached - Similar pages
Libya's Kebira Crater Apr 24, 2006 ... A huge crater in the Sahara desert, said to be the largest one ever found in the region, and dwarfing Arizona's "Meteor Crater", ...http://www.thunderbolts.info/tpod/2006/ ... kebira.htm
- 15k - Cached - Similar pages
Pictures of the Day have constantly harped on the fact that asteroids probably *can't* strike the Earth (see "Exploding Bolides"). They develop such intense electrical stress that they disintegrate at altitude. Peakskill was nothing but a few small stones when it finally reached Earth, for example. I think there's a Picture of the Day about Peakskill in the archive, as well.