Glacial Legacies of the Northeast US

How is a glacier an agent of erosion?

4-6 geologically recent ice ages glaciers covered almost all the land surface of the NE United States including New York and Vermont. This is probably what most of the area looked like at its peak about 20,000 years ago.

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GlacierGlacier: :

• • A mass of ice and surficial A mass of ice and surficial snow that persists throughout snow that persists throughout the year and flows outward or the year and flows outward or downhill like a fluid under its downhill like a fluid under its own weight. Most range in size own weight. Most range in size from 100 meters to 10’s of from 100 meters to 10’s of thousands of kilometers.thousands of kilometers.

Two types of glaciers:Two types of glaciers:• AlpineAlpine (form in (form in

mountains/valleys)mountains/valleys)• ContinentalContinental (exist at the poles, (exist at the poles,

advance covering continents)advance covering continents)

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Average Global Temperatures for the Past 500,000 years.The last continental glacier, dubbed the “Wisconsin” Ice Sheet,

receded approximately 10,000 years ago.

What causes Ice Ages?

• Milankovitch Theory: small, regular changes in the earth’s orbit and in the tilt of earth’s axis cause Ice Ages.

» Shape of earth’s orbit changes every 100,000 thousand years. (eccentricity of the ellipse)

» Tilt of earth’s orbit: (21.5 to 24.5 degrees)» Precession: circular movement of earth’s axis.

• Other: irregularities of the sun, volcanic dust, or position of the continents.

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Ice coverage of North America approximately 21,000 years ago

Retreat (melt back) of the glaciers with successive melt water lakes and rivers.

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The only part of New York that was clearly never covered by glaciers is Allegheny State Park in Western New York State.

Long Island was built by glacial sediment.

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How selected features of continental glaciation, including kames, originated.

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The alpine Athabaska Glacier in Alberta, Canada is one of the most accessible modern glaciers. Note the road and cars parked left of the melt water lake.

Which type of glacier is this?

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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.

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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.

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Debris from the continental glaciers was left behind as irregular terrain such as this terminal (end) moraine on Cape Cod.

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Locations of moraine deposits in New York State

Glacial till sediment, in some places hundreds of feet thick, covers most of New York State.

What can we say about the “sorting” of glacial till?How do we know these sediments weren’t eroded by water?

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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. 19

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.

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Terminal moraines form the backbone of Long Island and extend to the east.

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South Shore of Long Island (south of the Ronkokoma Moraine)

Sorted sand was deposited in this “outwash plain” as the glaciers melted and water deposited the sands in the plain.

The north shore of Long Island (Harbor Hill Moraine) looks a bit different! It has bluffs of unsorted glacial till dropped by the receding glacier. Rocks of diverse types settle onto the beach and are eroded by wave action.

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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.

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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.

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An esker is along US Route 6 in Northern Westchester County, NY.

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Another esker follows NY Route 79 north of Binghamton, NY.

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Parts of Route 79 were built right along the esker. (See the arrows.)

Eskers make a firm road base, that is well drained and can supply hgh quality sand and gravel.

(Lower Hudson River)

Glaciers transport “foreign” rocks!

Most of New York State does not have igneous or metamorphic bedrock, these rock types are common throughout the state in glacial deposits. 29

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.

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A glacial “erratic” or drop stone is an especially large transported rock. This one is almost the size of a house. It is located east of Tarrytown, NY.

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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. 32

Drumlins are elongated hills of unsorted sediment, usually aligned north-south. Drumlins form under continental glaciers. Hundreds of them can be seen between Rochester and Syracuse in Western New York State.

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This is pat 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.

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New York’s drumlin field is among the most extensive anywhere.35

Drumlins are eroded by wave action along the south shore of Lake Ontario at Chimney Bluffs County Park.

Fine clay binds the sediment the includes particles as big as large boulders. The unsorted sediment is an indication of ice deposited till.

Mr. Coyle grew up half a mile from here, this is where he swam as a little kid!

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Both alpine and continental glaciers scour broad “U-shaped valleys”. This is about a ten mile walk up the the alpine Castner Glacier.

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A V-shaped stream valley such as this in the Rocky Mountains of Colorado is the work of stream erosion.

Some New York streams, including the Genesee River in Letchworth Gorge carve out narrow V-shaped valleys. 39

Glaciers carved this broad U-shaped valley in the Rocky Mountains of Montana.

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U-shaped valleys such as this one in the western Finger Lakes are common in this part of New York State.

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The Finger Lakes 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.

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Portions of Seneca and Cayuga Lakes looking north from an airplane. Can you match them with the last image?

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Looking north along Canandaigua Lake in the Finger Lakes.

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Glacial erosion deepened the main north-south valley where the town of Montour Falls, NY is located. The glacial flow (river) was cut-off to create a “hanging valley. Similar to a waterfall.

Glacial polish and striations (diagonal to the top left) are displayed on this rock surface near Tarrytown.

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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.

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Grooves and glacial polish near Peekskill, NY document the southward movement of the ice. Also notice the stepped edges on the right (south) side.

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Glacially carved grooves (deep striations) are

common in the hard rocks of the

Adirondacks.

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Rocks carried by a glacier are often partially rounded and scratched by abrasion with other rocks.

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Chatter marks and crescent gouges on hard bedrock surfaces are more evidence of glacial movement.

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A whaleback (or roche mountonnée) is a bedrock surface that has been scoured on the north side and plucked on the south end. They are common in areas of hard crystalline bedrock.

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From this image it’s clear that the ice moved southward from left to right to produce whalebacks in Canopus Lake, Putnam County, NY.

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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. 54

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.

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But even the highest of the Adirondack Mountains have rounded summits eroded by the glaciers.

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A kame is a hill that has been deposited like a delta (meltwater) at the edge of a glacier. This kame is in a town park in Shortsville, NY, near Rochester.

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The courses of both the Niagara River and the Genesee River were

changed causing them to make dramatic new gorges and waterfalls.

The weight of the glaciers caused part of North America to sink.

Since the ice has melted, rebound is causing these depressed areas to slowly rise to their pre-glacial elevations.

Note Hudson Bay, which lies over a depressed part of Earth’s granitic continental crust.

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One result of postglacial isostatic rebound is these bays along the south shore of Lake Ontario. The north shore has rebounded more than the south shore, causing the lake to invade stream valleys. Sodus Bay is a good example. Lake Ontario

Pattern Ground

Pattern ground is rock pushed into polygons by the freeze-thaw cycles in a post-glacial climate. This image is a location in the Rocky Mountains, but similar patterned ground can be observed in some Catskill forest locations.

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Finger Lakes

Drumlin Field

Long Island Moraines

Polish, Grooves

Striations

Major regional features of the ice ages.

Valley Heads Moraine

Rounded Mountain Tops

Post-glacial Lakes

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Eskers, Kames

Till banks

Changed stream

channels

Evidence of Glaciers in VT

• Rounded mountain tops (abrasion)• Roche moutonnée topography (Camel's Hump is a

classic and well-known example, with a sloping north face and very steep south face)

• Lake Winooski and Lake Hitchcock (CT River)• Eskers• U-shaped valleys• Champlain Sea and the Charlotte Whale• Gravel and sand deposits along Lake Champlain• Striations and erratics• Glacial and Fjord-type lakes (Crystal Lake, Lake

Willoughby)

The Charlotte Whale

Camel’s Hump- Roche Moutonnee

Lake Willoughby

The end.

(until the next Ice Age arrives)

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