Transcript Glaciers Presentation - North Syracuse Central School District

Thomas McGuire, Cave Creek, AZ
Author, Amsco School Publications, NY
At least four geologically recent ice ages glaciers covered
almost all the land surface of New York State. This is probably
what most of the state looked like about 20,000 years ago.
#1
Glacier: A mass of ice and snow that
persists throughout the year and flows
outward or downhill like a fluid under its own
weight. Most range in size from 100 meters to
10,000 kilometers.
#2
#3
Ice coverage of North America approximately
21,000 years ago
The only part of New York that was clearly
never covered by glaciers is Allegheny State
Park in Western New York State.
#4
Long Island was
built by glacial
sediment.
#5
The alpine Athabaska Glacier in Canada is one of the most
accessible modern glaciers. Note the road and cars parked
left of the melt water lake.
Glaciers push, drag and carry great quantities of sediment
from clay size to boulders. The blue lines show the far
edge of this glacier about a quarter mile away. This is the
Castner Glacier in Alaska.
#6
#7
Two lateral (side) moraines beside the Athabaska glacier. Ice
flowing in the valley to the right has pushed these ridges of
unsorted till into place.
Debris from the continental glaciers was left behind as irregular (hummocky)
terrain such as this terminal (end) moraine on Cape Cod.
Locations of moraine deposits in New York State
Glacial till
sediment, in
some places
hundreds of
feet thick,
covers most
of New York
State.
#8
#9
Within moraines closed depressions are common. Some
may have been created by a block of ice melting within the
glacial deposits. Here we see ice on a former water surface.
The ice makes this kettle northwest of Oneonta especially
visible.
Terminal moraines form the backbone of Long Island and
extend to the east.
The Ronkokoma Moraine dips below
sea level at Montauk Point. This is
New York’s most eastern landfall. Note
the boulders washed out of the
moraine.
This hummocky, irregular land surface south of Naples,
NY is a part of the Valley Heads Moraine. The irregular
land surface and kettle holes are typical of moraines.
Sediment deposited
directly by the ice Is a
mixed jumble of
sediment from clay size
particles to large
boulders.
But this is layered
glacial outwash on
Long Island that is
deposited by water from
the melting glaciers.
Layering indicates
water deposits
while a jumble of
unsorted material is
a sign of glacial ice
deposits.
# 10
The north shore of Long Island has bluffs of
glacial till in the Harbor Hill Moraine. The
transported rocks of diverse types settle onto
the beach.
The sandy beaches along the south shore are composed of sorted outwash
sediment.
Glacial outwash
deposits are a
prime source for
high quality sand
and gravel.
Surprisingly. this
is New York
State’s most
economically
valuable
geological
resource.
The ice wall is the lower
end of the Castner
Glacier in central Alaska.
Glacial meltwater feeds
this fast flowing river
emerging from the
glacier. Much of the
melting occurs at the
bottom of the ice.
Long ridges called
eskers are sometimes
deposited in tunnels by
these subglacial
streams.
# 11
# 12
An esker is along US Route 6 in Northern Westchester County, NY.
Another esker follows NY Route 79 north of Binghamton, NY.
Glacial deposits such
as these at Croton
Point in the Lower
Hudson River contain
rocks that have been
transported by the
moving ice.
Although most of
New York State does
not have igneous or
metamorphic
bedrock, these rock
types are common
throughout the state
in glacial deposits.
# 13
Cobblestone homes
in Western New York
State were
constructed from
glacially deposited
stones that were
embedded in thick
mortar.
Many of these stones
differ greatly from the
composition of
nearby bedrock.
Some of them were
clearly transported
hundreds of miles
southward from
Canada.
# 14
An erratic is an especially large transported rock. This one is
almost the size of a house. It is located east of Tarrytown, NY.
Occasionally an erratic is left perched on top of smaller boulders after
many years of erosion. This perched erratic is at North Salem in
Westchester County.
# 15
Drumlins are elongated hills of unsorted sediment, usually aligned northsouth. Drumlins form under continental glaciers. Hundreds of them can be
seen between Rochester and Syracuse in Western New York State.
This is part of
drumlin field east
of Rochester, NY.
Note that the
trailing ends of the
hills are the
southern slopes.
The north slopes
are usually more
blunt.
# 16
# 17
New York’s drumlin field is among the most extensive anywhere.
Drumlins are eroded by wave action
along the south shore of Lake Ontar
at Chimney Bluffs County Park.
Fine clay binds the sediment the
includes particles as big as large
boulders. The unsorted sediment is
indication of ice deposited till.
#1
Both alpine and continental glaciers
scour broad U-shaped valleys. This is
the alpine Castner Glacier.
# 19
31
A V-shaped stream valley
such as this in the Rocky
Mountains of Colorado is
the work of stream
erosion.
# 20
Some New York streams, including the
Genesee River in Letchworth Gorge
carve out narrow V-shaped valleys.
In spite of it name, there are few glaciers left in
Glacial National Park. The permanent ice has
melted back so much that long-lasting snow fields
are now found where moving ice used to be.
Glaciers carved this broad U-shaped valley in the Rocky Mountains of Montana.
# 21
U-shaped valleys such as this one in the
western Finger Lakes are common in this part
of New York State.
35
# 22
The _______________of Western New York State were excavated as
U-shaped valleys by the glaciers advancing to the south. Moraines
dammed the former south flowing outlet rivers.
Portions of Seneca and Cayuga Lakes looking
north from an airplane. Can you match them with
the last image?
Looking north along Canandaigua Lake in the Finger Lakes.
Glacial erosion deepened the main north-south valley where the town of Montour Falls,
NY is located. But the east-west tributary valleys were not made deeper. So this
39
waterfall descend from a hanging valley.
Glacial polish and striations (diagonal to the top left) are
displayed on this rock surface near Tarrytown.
Striations can be
observed at about
4000 feet elevation on
Hunter Mountain in
the Catskills.
They show that the ice
was a minimum of a
mile thick over this
part of New York
State.
#2
Grooves and glacial polish near Peekskill, NY document the southward
movement of the ice. Also notice the stepped edges on the right (south)
side.
Glacially carved
grooves are
common in the hard
rocks of the
Adirondacks.
Rocks carried by a glacier are often
partially rounded and scratched by
abrasion with other rocks.
# 24
The Hudson River Valley from Cornwall to Peekskill is the only glacially
carved fjord on the east coast of North America. Ocean vessels can
travel all the way up to Federal Dam north of Albany.
The angular and jagged landscapes of the Southwest such as at
Monument Valley in Arizona, indicate an area that was never covered
by continental glaciers.
The highest
of the
Adirondack
Mountains
have
rounded
summits
eroded by
the glaciers.
How selected features of continental glaciation originated.
Retreat (melt back) of the glaciers with successive melt water lakes and rivers.
One of the melt water channels created a waterfall
more powerful than Niagara Falls that fell over these
cliffs at Clark Reservation in Syracuse. As you see,
the waterfall is now dry except for the plunge pool at
the bottom.
Image of Mt. Rainier,
Washington State
The end.
(…or is a new ice age right around the corner?)