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Fraser
2008-Nov-11, 01:30 AM
Ever since our recent encounter with asteroid 2008 TC3 — the first asteroid that was correctly predicted to hit our planet — I've had impact craters on the brain. Earth has about 175 known impact craters, but surely our planet has endured more bashing than that in its history. All the [...]

More... (http://www.universetoday.com/2008/11/10/earths-10-most-impressive-impact-craters/)

Ivan Viehoff
2008-Nov-11, 04:34 PM
The article refers to the Karakul impact crater in Tajikistan being at 6000m. I'm not quite sure exactly what she thinks is at 6000m, maybe the typical height of the mountains forming the rim. Several of the nearby mountains have peaks over 7000m. The shore of the lake is at about 3600m. I know because I have camped there. http://en.wikipedia.org/wiki/Karakul_Lake It has a road running alongside the shore, and a small village. Some of my friends have ridden bicycles along the road. These things don't happen at 6000m.

Well not usually. I met someone who rode a bicycle down from the top of one of the nearby mountains, Pik Lenin 7,134m. That is not only unusual, it is unique. http://www3.utsidan.se/corax-e/muztagh/tomasz.htm

BigDon
2008-Nov-11, 10:17 PM
Wow Ivan.

I met a Mongolian once who told me there isn't anywhere on Earth that a man can go to that a Brit hasn't been to.

I'm beginning to believe him.

stu
2008-Nov-12, 01:05 AM
The 6000 m refers to the local elevation. Just like the highland craters on Mars are on average "2000 m" above "sea level" vs. the ones in the northern plains being "2000 m" below "sea level."

Craters do not have rims that are 6 km above their floors. unless they're well over 1000 km in diameter (such as the Hellas impact basin on Mars, 2300 km in diameter and about 7 km deep from floor to rim).


Edit: Sorry, I should qualify my statement with it being applicable to planetary-sized bodies. For example, Hyperion has a crater that's ~120 km across but 10 km deep (the moon itself is 180x140x112 km). The final depth is proportional to the inverse of the gravity field of the body.

Ivan Viehoff
2008-Nov-12, 05:21 PM
The 6000 m refers to the local elevation. Just like the highland craters on Mars are on average "2000 m" above "sea level" vs. the ones in the northern plains being "2000 m" below "sea level."
Yes but which "local"? The crater floor (generally depressed), the crater rim (generally elevated), or the terrain beyond the rim (representing the terrain as if the crater was not there)? In the case of Karakul, neither the crater base, nor the general terrain beyond the rim are at a typical height of 6000m - I would suggest that there is no area on earth where the general terrain is at 6000m, only relatively localised mountain chains.

Ivan Viehoff
2008-Nov-12, 05:30 PM
I met a Mongolian once who told me there isn't anywhere on Earth that a man can go to that a Brit hasn't been to.
Americans don't travel to exotic places very much in comparison to Europeans. In part that is because you have so much variety of scenery within your own country there is less need to go abroad to find it. But unfortunately it leaves the USA generally with a lower level of knowledge of the Rest Of The World.

Tajikistan was very popular this year - with Europeans - because Tibet was closed.

stu
2008-Nov-13, 03:13 AM
Yes but which "local"? The crater floor (generally depressed), the crater rim (generally elevated), or the terrain beyond the rim (representing the terrain as if the crater was not there)? In the case of Karakul, neither the crater base, nor the general terrain beyond the rim are at a typical height of 6000m - I would suggest that there is no area on earth where the general terrain is at 6000m, only relatively localised mountain chains.

Ah, gotcha. I was answering the question without thinking about the numbers.

Yeah, I'm not sure there's any region on Earth that has, over a large area, an average elevation of 6 km above sea level. A quick check on Wikipedia says that the region is actually 3.9 km above sea level on average, though another Wikipedia page says 3.6 km. That's the (present-day) lake itself, so it would be probably mid-way up the crater depth (25-km lake inside a 45-km crater).

I would say, based on those two Wikipedia pages, that the article at the beginning of this thread is incorrect.

geonuc
2008-Nov-13, 09:48 AM
Over on geology.com, I found this cool Google Maps page showing the locations of fity impact craters:

http://geology.com/meteor-impact-craters.shtml