Pleistocene Glaciation of Pleistocene Glaciation of North AmericaNorth America

Pleistocene Ice AgesPleistocene 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 AmericaIce Ages in North AmericaContinental 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

FjiordsCoastal 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 & FlatDigital 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 DeltasOutwash 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.