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Geological > Geology of Long Island Sound
Figure 7:  17,500 - 15,500 Years Ago
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A View of Connecticut and the Drained Lakebed of Glacial Lake Connecticut, About 15,500 Radiocarbon Years Ago

The spillway for glacial Lake Connecticut was located across a low spot on the Orient Point-Fishers Island moraine, at a place now known as the Race. The spillway for the lake that occupied the Block Island Sound basin crossed a low spot in the terminal moraine just east of Montauk Point. Water issuing from this lake system flowed southward to the sea trough Block Channel. As the spillways were eroded, lake levels dropped.

By around 15,500 years ago, worldwide melting of the Wisconsinan ice sheet had started to contribute to a rise in sea level. Locally, the ice front stood near the Massachusetts border, and the shore of the rising sea was still well south of the terminal moraine. Erosion of the spillway across the terminal moraine had allowed the lake in the Block Island Sound basin to steadily lower, and eventually drain completely. This sequence of events lead to a similar fate for glacial Lake Connecticut, as the spillway at the Race slowly yielded to erosion. An east-flowing stream system developed on the exposed bed of glacial Lake Connecticut. This drainage took a turn to the south as it passed through the Orient Point-Fishers Island moraine, and headed for the sea across the drained lakebed in the Block Island Sound basin.

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