Friday, February 23, 2007

Friday Geology Pic: Lake Superior

Lake Superior from Space!

I've been talking with some friends about a possible trip this year, and we're thinking we might head towards the Lake Superior area...specifically the North Shore (the shore that borders with northern Minnesota).

The great thing about Lake superior, is that 1. Its beautiful. the waters are blue, and overlooking the cliffs and the lake shores, the water is nice and clear.

2. Its geologically great. I went college up in the midwest, and unfortunately alot of the people and professors tend to focus on the glacial history of the area. Afterall, the glaciers created Lake superior, and its the absence of glaciers that are slowly draining the lake via isostatic rebound. But I think there's an even more elegant story along its shores, one thats far more dynamic and spans BILLIONS of years of geologic time.

Lake Superior kind of looks like a finger pointing to the southwest. Its has a long linear axis that trends NE/SW. This axis is actually the trace of what geologists call and aulacogen. Its basically a valley where the old north american tectonic plate actually tried to rip itself in failed of course, and left this dramatic valley on the earth's surface. Similar events are taking place in East Africa right now, you may have heard of the east african rift.

The East African Rift is home to my single favorite volcano ever, Ol Doinyo Lengai - its lava flows BLACK and cools WHITE, definately check out the fucking sweet pics here. But I digress....

...Anyhow, much later, glaciers followed along this valley, and once they melted and receded, the valley filled up to form Lake Superior.

Whenever you drive along the North Shore, or even into the Upper Peninsula of Michigan, all the rocks you see are really really really old basaltic lava flows, and related sediments. these basalts formed as the plate was tearing apart, creating large fissure eruptions. Even though these flows are older than 1.8 billion years, you can still see some of their original flow features in exposures all along the shoreline.

Picture of Shovel point at tettagouche state park along the north shore of Lake Superior (its the ridge in the back). Shovel point is a thick exposure of basalt lava formed during the aulacogenic event back in the Proterozoic.

I think thats pretty cool. Most losers will only tell you about huge glaciers forming lake superior, but Lake Superior's beginning was actually Billions of years before the glaciers ever covered the land...and this lake of water, started as a valley of hellish LAVA.

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