Illustration by Karl Anslanslin
When you think of the word delta what pops into your mind? Our guess is the word Nile. The Nile Delta is likely the most widely known. Then perhaps the Mississippi Delta or the Amazon Delta. But the Oneonta Delta? That doesn’t even seem to make sense, does it? How could there even be an Oneonta Delta. Deltas form when large rivers flow into (large) oceans. Right? We have spent a lot of time in Oneonta. There is a large river there, the Susquehanna, but we never noticed an ocean, not even one of them! Looks like we have some explaining to do, doesn’t it?
The Ice Age history here has been studied by professional glacial geologists, most notably our friend Dr. Jay Fleisher, retired professor of geology at Oneonta State. Much of what follows are his thoughts, but we have added a few of our own views. Take a look at the yellow part of our map, courtesy of Karl Anslanslin. Yep, that’s the Oneonta Delta. This vicinity is known as Center City, Oneonta. Have you been there? It’s the flat part of town. Drive across it and you will see that most of it is indeed flat. But the southwest end drops downhill relatively quickly. There is a story here - the story of a delta.
There is no ocean, but the Susquehanna River Valley was once filled with water to make a sizable lake, called Glacial Lake Otego. The blue on our map is part of the lake bottom. There were two creeks that flowed into that lake. Each one carried a lot of sediment and each one deposited that sediment into the lake. Those were the beginnings of two deltas; each deposited in the waters of Lake Otego. As those two grew they expanded into each other and formed a single feature that we can properly call the Oneonta Delta. You might think of it as being a compound delta. It’s important to know that deltas always have nearly flat tops. Their sediments were deposited right up to lake levels. And lake levels are flat.
So now we have learned a lot about the Ice Age at Oneonta. The whole of Center City Oneonta lay beneath the waters of Lake Otego. Those waters filled with sediments and those sediments created the flat part of the town. But there is a lot more to the story. Look at the green parts of our map. Those are labeled alluvial fans. What happened is that there came a moment when all the waters of Lake Otego drained away. That left the delta high and dry. But those two creeks were still carrying large amounts of sediment. Those sediments were spread out across the old delta top as two sloping fans of earth – two alluvial fans. That’s important as, starting next week, we shall begin writing a series of columns about alluvial fans.
Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com.”
