ran@ho95e.UUCP (ran) (08/05/85)
Does anybody out there know about the origin of the Great Lakes (and have any newer theories come out lately, particularly with regards to plate tectonics and hot spots)? I remember learning that they were supposedly formed (though I don't know whether that means "created" or "put into their present form") during the Ice Ages. However, I have trouble understanding this. If you look at them (in particular, Superior, Michigan, and Huron), they are *very deep*. For instance, Superior is 1300 feet deep. With the surface at about 600 ft, it extends 700 feet below sea level. Michigan and Huron do the same (but not by as much). How did glaciers manage to dig these lakes so deep????? Other glacial lakes (Manitoba, Great Slave) are relatively shallow. I'm wondering if some plate tectonics might be involved here. The only other inland areas below sea level I can think of had tectonic causes (Death Valley, Dead Sea, Caspian Sea, Loch Ness). Might the Great Lakes be the remnant of a failed rifting (which was much later covered by ice)? I'm struck by the three way shape of the 3 lakes, which is typical of riftings (see the Horn of Africa, for instance). However, I know nothing of the geology of the area (except that they sit where the Canadian Shield pokes through). Does the geology blatantly contradict the above guess, or is it a possibility? Thanks.
eugene@ames.UUCP (Eugene Miya) (08/08/85)
> Does anybody out there know about the origin of the Great Lakes > (and have any newer theories come out lately, particularly > with regards to plate tectonics and hot spots)? > > Michigan and Huron do the same (but not by as much). How did glaciers > manage to dig these lakes so deep????? Other glacial lakes > (Manitoba, Great Slave) are relatively shallow. > > I'm wondering if some plate tectonics might be involved here. The only > other inland areas below sea level I can think of had tectonic causes > (Death Valley, Dead Sea, Caspian Sea, Loch Ness). Might the Great Lakes > be the remnant of a failed rifting (which was much later covered by ice)? First, I should say that I an not a geologist by training, but have worked with glaciologists. DO NOT UNDER-ESTIMATE the powers of frozen water! New theories in this area are not necessarily better. I don't think tectonic activity is greatly involved in the case of the Great Lakes. You would see relatively recent evidence of this, however, let me point you to the latest issue of Time Mag. Research is taking place in Superior which will shed more light on it's formation. Patience! --eugene miya NASA Ames Research Center {hplabs,ihnp4,dual,hao,decwrl,allegra}!ames!aurora!eugene emiya@ames-vmsb
shindman@utcs.UUCP (Paul Shindman) (08/09/85)
Although the exact origin escapes me right now, I do know that
there is one heckuva good film about it entitled "The Rise and
Fall of the Great Lakes" that was produced by the National Film
Board of Canada.
Anyone who wants more info on this film should contact their local
library (if they also have films) or send me e-mail and I'll look
up the details.
--
-----------------
Paul Shindman, U of T Computing Services, Toronto (416) 978-6878
USENET: {ihnp4|decvax}!utcs!shindman
BITNET: paulie at utoronto IP SHARP MAIL: uoftdoug@escher.UUCP (Douglas J Freyburger) (08/09/85)
> If you look at them (in particular, Superior, Michigan, and Huron), > they are *very deep*. For instance, Superior is 1300 feet deep. > With the surface at about 600 ft, it extends 700 feet below sea level. > Michigan and Huron do the same (but not by as much). How did glaciers > manage to dig these lakes so deep????? Other glacial lakes > (Manitoba, Great Slave) are relatively shallow. Sorry, but most of the Great Lakes are *very shallow*. It is hard to find a place in Erie, Superior, and Huron more than about 100 feet deep, and most of Michigan is less than 200 feet deep. Only Ontario is *very deep*, common several of hundreds. Given this shallowness, glacier dredging seems reasonable. On a clear day, I remember being able to see the floor the Erie (in the 70s, but not the 60s). > I'm wondering if some plate tectonics might be involved here. The only > other inland areas below sea level I can think of had tectonic causes > (Death Valley, Dead Sea, Caspian Sea, Loch Ness). Might the Great Lakes > be the remnant of a failed rifting (which was much later covered by ice)? Well, there used to be a mountain range there a VERY long time ago. The Catskills (sp?), the Boston Hills on the US side, and something else in Western Ontario. I might be missing badly here, this is from my high school geography course. There is a nice ridge that runs long the southern shore of lake Ontario, though. It goes from somewhere in New York or Vermont that extends through the start of Niagara Falls' gorge. There are different types of rock on each side of this escarpment. Was there a meeting an older Canadian shield with an older American shield VERY long ago to form that mountain range, and the escarpement that exists there now? If so, it would make the depth of lake Ontario easier to explain. Doug Freyburger DOUG@JPL-VLSI, DOUG@JPL-ROBOTICS, JPL 171-235 ...escher!doug, doug@aerospace, Pasadena, CA 91109 etc.
ayers@convexs.UUCP (08/14/85)
/* ---------- "Geology (Great Lakes) Question" ---------- */ >Does anybody out there know about the origin of the Great Lakes >(and have any newer theories come out lately, particularly >with regards to plate tectonics and hot spots)? > >I'm wondering if some plate tectonics might be involved here. The only >other inland areas below sea level I can think of had tectonic causes >(Death Valley, Dead Sea, Caspian Sea, Loch Ness). Might the Great Lakes >be the remnant of a failed rifting (which was much later covered by ice)? For the latest on plate tectonics, see the most recent issue of National Geographic... > If you look at them (in particular, Superior, Michigan, and Huron), > they are *very deep*. For instance, Superior is 1300 feet deep. >>Sorry, but most of the Great Lakes are *very shallow*. It >>is hard to find a place in Erie, Superior, and Huron more >>than about 100 feet deep, and most of Michigan is less than >>200 feet deep... Time magazine, August 12, 1985, pg. 49: "...on the first submarine exploration to the bottom of one of the world's biggest bodies of fresh water, Lake Superior...using the _Sea-Link_, they have been able to plunge right to the bottom. The deepest point: 1,330 ft." Well, that's one mystery less... blues, II