A visit to the floor of an ancient lake – Lake Leeds 9-1-16

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The ghost of a lake
Windows Through Time
Robert Titus

A-7 leeds

Picture caption – View from Sandy Plains Road, on the shore of Lake Leeds, looking out upon the lake basin.

The ghosts of the past are to be seen everywhere. Take a drive west from Leeds on old Rt. 23B. If there are ghost towns, then I guess there are ghost highways too. Pay attention as you drive along the highway and you will see the ghosts of a long-lost tourist trade. All along the road you will see mostly empty, sometimes abandoned motels and cabins and boarding houses. They were all busy, a half century ago. Back then, this highway had a thriving summer tourist trade. Families drove out from the city and spent a day, a week or even a month up here. I am not sure what all they did, but I suspect the clean fresh air had a lot to do with them coming here. Now it is all gone. There is a big difference between a depressed industry and a nearly extinct one. When I drive down the road, I imagine the Fourth of July weekend of 1959; it was different then.
But there are other ghosts and these ones are a lot older and often a lot harder to see. They don’t come out at night; they are best seen in the broad summer daylight. If there are ghost highways, and ghost industries, then they are also ghost lakes. They can be found in the very same places, too.
Head west, again on Rt. 23B from Leeds. Just past the famous Leeds Bridge notice how the landscape changes quickly. Left and south of the highway is a very flat landscape. It stretches off for quite a distance. There are few good reasons to take notice of this landscape; it is so monotonous. But the geologist looks through a time window and sees the past. This is the floor of an ice age lake.
Suddenly it is about 14,000 years ago. All around it is dark and cold and it is all water. The water is not that deep, but it is murky and very little sunlight filters down to reach the floor of the lake where we are. The lake bottom, all around us, is just dull mud: gray and very cold. Up above, a little sunlight can be seen and, drifting by, are small bergs of ice.
It’s time to move on. Driving about three and one half miles west you reach South Cairo. Turn right on County Rt. 67 and cross the flat lake bottom here. On the other side turn right again onto Sandy Plain Road, and drive back east a short distance. Now, spread out in front of you, is the basin of the lake. You have not likely ever seen an ice age lake before and this is a good one. The flat floor of the valley is the old lake bottom. You can look around and imagine the old shore line. You are pretty much standing on that shore. Continue further east on Sandy Plain Road and turn right onto Indian Ridge Road. You will, in fact, see a ridge of rock here, but to your left, I am guessing is an ice age delta that was deposited in the old lake. This delta was the product of Potic Creek which stills flows south as a tributary of Catskill Creek.
Back, when this was a lake, Potic Creek flowed into it and carried enormous amounts of sediment with it. These deposits were dumped in the lake and piled up as the delta. The top of the delta lies at about 225 feet above sea level. That is an important figure; delta tops mark the approximate level of the lake. The lake bottom lies at just about 140 feet. That makes the old lake as having been 85 feet deep.
The lake stretched out six miles from its eastern edge at the Leeds Bridge. It was a mile across, at its widest and generally about 80-90 feet deep. It was, thus, a pretty good sized lake. But it is gone, entirely gone. What happened to it?
The canyon we visited last week, Austin Glen, stretches east from Leeds. This canyon did not, I think, exist at the time of the lake. Instead, a ridge of rock stretched out across the valley. That comprised the dam which impounded the waters of the lake we have been visiting. Today’s Austin Glen was carved through this ridge by torrents of water that flowed through the lake and on to the south. When the canyon was completely excavated, all the water drained out of the lake and it was no more. Today, it exists only in the mind’s eye of the perceptive geologist. When I drive down the highway, to me it becomes the Fourth of July weekend, 12,991 BC. It was different then. Reach the author at titusr@hartwick.edu

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