Pleistocene Glaciation of North America

Pleistocene Ice Ages

Direct Effects of Past Glaciation –Most of the soil and sedimentary rocks were scraped off of underlying crystalline rock in northern and eastern Canada –Future lake basins were gouged out of the bedrock –Extensive sets of recessional moraines were left behind by retreating ice sheets in the upper midwestern U.S. and in Canada

Indirect Effects of Past Glaciation Large pluvial lakes (formed in a period of abundant rainfall) existed in closed basins in Utah, Nevada and eastern California –Great Salt Lake is a remnant of the much larger pluvial Lake Bonneville –Huge floods emanated as ice-dammed lakes (e.g., Lake Missoula) drained catastrophically Sea level was significantly lowered by large amounts of water locked up into ice sheets, allowing stream channels and glaciers to erode valleys below present-day sea level Giant gravel ripples formed during draining of Lake Missoula

Ice Ages in North America Continental Glaciers advanced & Receded at least 4 times during past 2 million years During glacial advances, sea level drops exposing continental shelf Maximum advance of last glacier 18,000 yrs ago Sea level rises 300 ft by 8,000 yrs, resulting in present coastline

Evidence of Glaciation in the U.S.

End Moraines in the Contiguous United States and Canada

Fjiords Coastal inlets formed by drowning of glacially carved valleys by rising sea level

The Great Lakes

Origin as Meltwater Lakes

NY State’s Finger Lakes

Kettle Lakes

Ice Lobes in New York State

Retreat of the Wisconsinan Glacier (A)Maximum extent of ice about 21,750 years ago (B)14,000 years ago – retreating glacier (C)12,000 – 13,000 years ago

Retreat of the Wisconsinan Glacier Stages D, E, and F occurred 11,000 to 12,000 years ago The final stage was approximately 11,000 years ago

Long Island Glaciation

Continental Glaciers Retreat forming Long Island of Today Lakes form as ice sheet melts Sea Level Rises LI Sound fills with water from Ocean LI takes modern form (from Newsday “Long Island Our Story”

Major Landforms of Long Island

Long Island Moraines

Topography of Long Island North Shore: Irregular Coast & Hilly South Shore: Straight Coast & Flat Digital Elevation Model: 2X Vertical Exaggeration (Bennington, 2003) Data from NYSDEC & Cornell University

Glacial Features of LI Lake Ronkonkoma Ronkonkoma Moraine Harbor Hill Moraine Kames Outwash Plain

Glacial Till Unsorted Sediments were deposited directly by ice. Round shape of many boulders indicates that they were also shaped by running water Eroding moraine at Montauk Boulders at Orient

Glacial Features of Smithtown & Central LI Outwash Plain Ronkonkoma Moraine Harbor Hill Moraine Lake Ronkonkoma

Harbor Hill Moraine Till of Harbor Hill Moraine overlying outwash deposits (RTE 25 A, Setauket) Closeup view of Till of Harbor Hill Moraine consisting of unsorted silt, sand, pebbles, and cobbles

Kame Deltas indicate large pro-glacial lakes as continental glacier melted Kame Deltas Outwash Plain Harbor Hill Moraine Note: Kame Deltas overlie Ronkonkoma Moraine What does this indicate about the relative age of the Deltas? Ronkonkoma Moraine

Glacial Features of Huntington Area Outwash Plain Outwash Channels Harbor Hills Moraine Delta Deposits

Delta Deposits at Caumsett The sediments in the cliffs formed when streams of water carrying sand and gravel gushed from the glacier and entered the lake. The faster the water the larger size sand grains, pebbles or boulders it can carry. Upon reaching the still water, the streams slowed and dropped their sediments forming a delta.

Weathering breaks rocks down & Erosion wears away land & transports sediments Frost Action split this rock Erosion of bluffs at Caumsett, forming fan

Rivers Erode the Land Nissequogue River Carman’s River Ronkonkoma Moraine Smithtown Harbor

Carman’s River Carman’s River cuts through the Ronkonkoma Moraine.