Examples of Glacial Erosion in New York

Glacial Activity

Glacial stages in North America

• The major glacial stages of the current ice age in North America are the Illinoian, Sangamonian and Wisconsin stages.

• During the most recent North American glaciation, during the latter part of the Wisconsin Stage (26,000 to 13,300 years ago), ice sheets extended to about 45 degrees north latitude. These sheets were 3 to 4 km thick.

• This Wisconsin glaciation left widespread impacts on the North American landscape. The Great Lakes and the Finger Lakes were carved by ice deepening old valleys. Most of the lakes in Minnesota and Wisconsin were gouged out by glaciers and later filled with glacial meltwaters.

Northern hemisphere glaciation during the last ice ages. The accumulation of 3 to 4 km thick ice sheets caused a sea level lowering of about 120 m. Also, the Alps and the Himalayas were covered by glaciers. Winter sea ice coverage was much more limited in the south.

Courtesy by: John S. Schlee (2000) Our changing continent, United States Geological Survey.

Appalachian PlateauThe Appalachian Plateau was glaciated many times, and deposits of previous glaciations were eroded and redeposited during later glaciations. Thus, exotic-rich stratified sediments in valleys were recycled and moved farther south within valleys during each episode of glaciation. Evidence of this reworking is seen in the fragments of glacial conglomerate found in valleys throughout central New York. These are pieces of carbonate-cemented glacial gravel reworked from deposits of previous glaciations. Cementation of gravel took place in the vadose zone (above water table) during ice-free periods after each glaciation. At least three generations of glacial conglomerates are preserved--postglacial, mid-Wisconsin and pre-Wisconsin (Aber 1979). The Appalachians - USGS

FJORDS

The Finger Lakes

The Finger Lakes are often described as inland fjords because of their deeply eroded bedrock valleys and thick sediment infill. A dozen lakes are found in two groups--eastern and western. These lakes occupy deep ice-carved valleys.

Near-vertical space photograph of the Finger Lake district of central New York. Space-shuttle photo STS 51B-33-028, 4/85.

The Finger Lakes The Finger Lakes were formed by glacial activity during the Pleistocene epoch (Ice Age), which began about 100 million years ago. The first glacier affecting the region was reportedly 2,500 feet thick and had a cap of crusted ice about 200 feet thick, which was carried along by the sheer mass of the glacier. It was believed to have traveled at a rate of two to three feet per day and expanded southward across New York State, extending as far south as Williamsport, Pennsylvania.

Waterfall at Finger Lakes, New York Copyright 2008 Toby Thornton

Hudson River

The Hudson River is a Fjord. The valley was partially carved by a southward advancing ice sheet (or continental glacier). When the glaciers melted, rising sea level flooded the Hudson River Valley with sea water. Copyright 2010 New York Yacht Club. All Rights

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Glacial Grooves and Striations

Cloisters Museum and Fort Tryon Park

This rock and wall is at the Cloisters Museum in New York City (on Manhattan Island). What are the "scratches" called, and how do they form? Why are they in New York City? Glaciers once covered the New York City area. The moving ice scraped the bedrock producing glacial groove and striations. The glaciers that once covered New York have since melted.

Central Park

• Glacial striations are widespread in Central Park. Best seen after rain and in low-angle light, the parallel sets of striae transect the structures of the schist bedrock. Image by Brett Bennington

Central ParkThe striations that form on these rocks, were caused as debris is dragged across the glacier bed. Many of the exposures preserve glacially-polished surfaces, striations, and grooves carved from rocks embedded in the base of the ice sheet as it moved southward. Crenulation or Crenulation cleavage is a texture formed in metamorphic rocks such as phyllite, schist and some gneiss by two or more stress directions resulting in superimposed foliations.

Photos courtesy by Garret Miller

Central Park

• Glaciers left their mark all over New York's Central Park. To the right is a glacially scoured outcrop of gneiss and schist on the west side of the park, with the Midtown skyline behind. Photo courtesy of the U.S. Geological Survey.