Transcript North American Glaciation

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
Harbor Hill Moraine
Ronkonkoma Moraine
Outwash Plain
Kames
Glacial Till
Eroding
moraine
at
Montauk
• Unsorted Sediments were
deposited directly by ice.
• Round shape of many
boulders indicates that they
were also shaped by running
water
Boulders
at Orient
Glacial Features of Smithtown & Central LI
Harbor Hill Moraine
Lake
Ronkonkoma
Outwash Plain
Ronkonkoma
Moraine
Harbor Hill
Moraine
Closeup view of Till of
Harbor Hill Moraine
consisting of unsorted silt,
sand, pebbles, and cobbles
Till of Harbor Hill Moraine
overlying outwash
deposits
(RTE 25 A, Setauket)
Kame Deltas indicate large pro-glacial lakes as
continental glacier melted
Harbor Hill Moraine
Ronkonkoma
Moraine
Outwash Plain
Kame
Deltas
Note: Kame Deltas overlie Ronkonkoma Moraine
What does this indicate about the relative age of the Deltas?
Glacial Features of Huntington Area
Delta Deposits
Harbor Hills
Moraine
Outwash Plain
Outwash
Channels
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
Smithtown
Harbor
Carman’s River
Nissequogue River
Carman’s River
Carman’s River cuts
through the Ronkonkoma
Moraine.