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Lake Iroquois Brain Dump
Apr. 5th, 2007 02:52 pmSo, one major part of my project is figuring out the deglaciation of the Finger Lakes region to get at when incision started. Ice sheet melts, incision starts- simple, right?
Well, yeah, it would be- if it weren't for glacial lakes.
When the ice sheet started to melt back, massive proglacial lakes formed in front of the retreating ice front. You can see their modern counterparts in places like this one. Because of the Valley Heads Moraine to the south, these lakes couldn't drain that way, and just kept building up as the ice melted. The lakes coalesced, and became Glacial Lake Iroquois.
Finally, just before the ice sheet melted back toward the Mohawk River Valley, the lakes reached a high stand. This wasn't because any more water was being added- a lot was about to be taken away. As soon as the ice melted past the Mohawk River Valley, a good portion of Lake Iroquois rushed out through the valley and into the Atlantic Ocean- catastrophic drainage number one.
Eventually, the water found a level where the Mohawk River Valley was just an outlet- not a catastrophic outlet. After that, things aren't quite as clear. Right on top of Watkins Glen lies two deltas, one on top of the other. It's not a proglacial delta- for one, there's not enough silt and clay in it to convince me. Plus, the orientation of the delta foresets really makes it tempting to think that it was formed by the stream that has since eroded through it- it's exactly what you'd expect. This really makes me think that the lower delta might be another lake stage, one that's been documented in the literature.
After the Mohawk Valley catastrophic drainage, the level of Lake Iroquois would have remained relatively stable. As more ice melted, any extra water that wouldn't fit into the increased volume left by the ice would have just drained into the Atlantic Ocean through the Mohawk River, until isostatic rebound made it too high to get to (note- look into that). However, there was one more valley to the north- the Hudson River Valley. After the ice melted past that... well, end of the party for Lake Iroquois. It pretty much drained away to almost nothing; only Lake Ontario and Lake Champlain remain of a massive body of fresh water that once covered most of Upstate New York.
This is a really tantalizing explanation of what I'm seeing, and it would really make the determination of when incision began much easier. The last catastrophic discharge is considered to have triggered the well-constrained Intra-Allerød cold period, and when that drained out, incision would have pretty much started right then. However, from reading the literature, it doesn't look like Lake Iroquois had a shoreline that far south when it drained out of the Hudson. One interpretation puts it close-within a couple of tens of kilometers- but it wasn't quite there.
But if it wasn't there, what am I seeing?
UPDATE: I spoke with my advisor this morning- he feels I'm correct in making the argument that the deltas were from Lake Iroquois, and suggested I write a paragraph about it in my thesis. Well, that saves me a lot of time, but I'd still like to sit down and look at a few of these things.
We made a bit of a deal- if he supports me this summer, I graduate in August. Well, I was going to do that anyway, but if it means I get support now...
Well, yeah, it would be- if it weren't for glacial lakes.
When the ice sheet started to melt back, massive proglacial lakes formed in front of the retreating ice front. You can see their modern counterparts in places like this one. Because of the Valley Heads Moraine to the south, these lakes couldn't drain that way, and just kept building up as the ice melted. The lakes coalesced, and became Glacial Lake Iroquois.
Finally, just before the ice sheet melted back toward the Mohawk River Valley, the lakes reached a high stand. This wasn't because any more water was being added- a lot was about to be taken away. As soon as the ice melted past the Mohawk River Valley, a good portion of Lake Iroquois rushed out through the valley and into the Atlantic Ocean- catastrophic drainage number one.
Eventually, the water found a level where the Mohawk River Valley was just an outlet- not a catastrophic outlet. After that, things aren't quite as clear. Right on top of Watkins Glen lies two deltas, one on top of the other. It's not a proglacial delta- for one, there's not enough silt and clay in it to convince me. Plus, the orientation of the delta foresets really makes it tempting to think that it was formed by the stream that has since eroded through it- it's exactly what you'd expect. This really makes me think that the lower delta might be another lake stage, one that's been documented in the literature.
After the Mohawk Valley catastrophic drainage, the level of Lake Iroquois would have remained relatively stable. As more ice melted, any extra water that wouldn't fit into the increased volume left by the ice would have just drained into the Atlantic Ocean through the Mohawk River, until isostatic rebound made it too high to get to (note- look into that). However, there was one more valley to the north- the Hudson River Valley. After the ice melted past that... well, end of the party for Lake Iroquois. It pretty much drained away to almost nothing; only Lake Ontario and Lake Champlain remain of a massive body of fresh water that once covered most of Upstate New York.
This is a really tantalizing explanation of what I'm seeing, and it would really make the determination of when incision began much easier. The last catastrophic discharge is considered to have triggered the well-constrained Intra-Allerød cold period, and when that drained out, incision would have pretty much started right then. However, from reading the literature, it doesn't look like Lake Iroquois had a shoreline that far south when it drained out of the Hudson. One interpretation puts it close-within a couple of tens of kilometers- but it wasn't quite there.
But if it wasn't there, what am I seeing?
UPDATE: I spoke with my advisor this morning- he feels I'm correct in making the argument that the deltas were from Lake Iroquois, and suggested I write a paragraph about it in my thesis. Well, that saves me a lot of time, but I'd still like to sit down and look at a few of these things.
We made a bit of a deal- if he supports me this summer, I graduate in August. Well, I was going to do that anyway, but if it means I get support now...
