POW! Take That, Triassic!

Spectacular image of The Manicouagan Reservoir (impact structure), in Quebec. 70 Km= ~42 miles, so roughly 125 miles in circumference, that would be a really fun boating and camping trip. I'd bet there's some spectacular geology to be seen as well. (click the pic for hugeness)

The lake actually surrounds the central uplift of the impact structure, which is about 70 kilometers in diameter and is composed of impact-brecciated (relativley large pieces of rock embedded in finer grained material) rock. Glaciation and other erosional processes have reduced the extent of the crater, with the original diameter estimated at about 100 kilometers.

The impact that formed Manicouagan is thought to have occurred about 212 million years ago, toward the end of the Triassic period. Some scientists believe that this impact may have been responsible for a mass extinction associated with the loss of roughly 60% of all species. It has been proposed that the impact was created by an asteroid with a diameter of about 5 kilometers.

Oddly, the reason I actually went and looked at the full-sized version of this was not for the geology- I've seen numerous pictures of this structure- but because I wanted to look at the clouds more carefully. Note that the little cotton-ball cumulus are absent wherever there is any significant water. I'm guessing the cumulus are forming from spotty summer convective updrafts. Under those conditions, the water will be cooler than the land, so the air won't rise there. In fact, that would be where the air that has ascended and cooled would descend again. As air rises and decompresses, it cools; when it cools to the dewpoint, clouds form. As the air descends again, it recompresses and warms up. Any cloud droplets in the warmer air evaporate, and the cloud disappears. Note that the contrails crossing the ring structure do continue across it- they're well above the convection cells. Airliners like to fly right near the top (or just over) of the mixing layer of our atmosphere, the troposphere, to avoid the turbulence associated with that mixing,

The geology is pretty neat too: I hadn't realized this impact had been associated with the Triassic extinction. (Don't take this to mean "This impact caused that extinction." Note the weasel words in the excerpt above: "Some scientists believe..." kind of indicating that there is not a strong concensus on the point.) I also hadn't noticed the oddly circular "horns" sticking off the ring at about the 11 o'clock position in this image. I suspect that is merely happenstance. While at a glance it looks like an adjacent impact, if it was, I think it would have been studied and widely known.

Just checked Wikipedia to see if I could find any info to support some geospecualtion regarding what I think I see, and it asserts pretty strongly that this was not the cause of the Triassic-Jurassic extinction. Regarding the regional geology, it doesn't say much, so I'll keep my speculatin' to myself.

I'd love to visit that island!