1. Glacial Legacies of the Northeast US

2. How is a glacier an agent of erosion?

3. 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.
3

4. 4
GlacierGlacier::
•• A mass of ice and surficial snowA mass of ice and surficial snow
that persists throughout the year andthat persists throughout the year and
flows outward or downhill like a fluidflows outward or downhill like a fluid
under its own weight. Most range inunder its own weight. Most range in
size from 100 meters to 10’s ofsize from 100 meters to 10’s of
thousands of kilometers.thousands of kilometers.
Two types of glaciers:Two types of glaciers:
• AlpineAlpine (form in mountains/valleys)(form in mountains/valleys)
• ContinentalContinental (exist at the poles,(exist at the poles,
advance covering continents)advance covering continents)

7. 7
7
Average Global Temperatures for the Past 500,000 years.
The last continental glacier, dubbed the “Wisconsin” Ice Sheet,
receded approximately 10,000 years ago.

8. 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.

9. 9
Ice coverage of North America approximately 21,000 years ago

10. Retreat (melt back) of the glaciers with successive melt water lakes and rivers.
10

11. 1111
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.

12. 12
How selected features of continental glaciation, including kames, originated.

13. 13
The alpine Athabaska Glacier i
Alberta, Canada is one of the
most accessible modern glacie
Note the road and cars parked
left of the melt water lake.
Which type of glacier is this?

14. 14
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.
1414

15. 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.
1515

16. 16
Debris from the continental glaciers
was left behind as irregular terrain such
as this terminal (end) moraine on Cape
Cod.
16

17. 17
Locations of moraine deposits in New York
State

18. 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 18

19. 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

20. 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.
20

21. Terminal moraines form the backbone of Long Island and extend to the east.
21

22. 22
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.

23. 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.
2323

24. 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.
24

25. 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.
25

26. An esker is along US Route 6 in Northern Westchester County, NY.
26

27. Another esker follows NY Route 79 north of Binghamton, NY.
27

28. 28
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.

29. (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

30. 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.
30

31. 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.
3131

32. 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

33. 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.
33

34. 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.
34

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

36. 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!
36

37. 37
Both alpine and continental glaciers
scour broad “U-shaped valleys”. This is
about a ten mile walk up the the alpine
Castner Glacier.
37

38. 38
A V-shaped stream valley such
as this in the Rocky Mountains
of Colorado is the work of
stream erosion.

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

40. Glaciers carved this broad U-shaped valley in the Rocky Mountains of Montana.
40

41. U-shaped valleys such as this one in
the western Finger Lakes are
common in this part of New York
State.
4141

42. 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.
4242

43. Portions of Seneca and Cayuga Lakes looking north from
an airplane. Can you match them with the last image?
43

44. Looking north along Canandaigua Lake in the Finger Lakes.
44

45. 45
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.

46. Glacial polish and striations (diagonal to the top left) are
displayed on this rock surface near Tarrytown.
46

47. 47
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.

48. 48
Grooves and glacial polish near Peekskill, NY document the southward
movement of the ice. Also notice the stepped edges on the right (south)
side.
48

49. 49
Glacially carved
grooves (deep
striations) are common
in the hard rocks of the
Adirondacks.
49

50. Rocks carried by a glacier are
often partially rounded and
scratched by abrasion with 50

51. Chatter marks and crescent gouges on hard
bedrock surfaces are more evidence of
glacial movement.
5151
51

52. 52
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.
52

53. 53
From this image it’s clear that the ice moved southward from left to right to
produce whalebacks in Canopus Lake, Putnam County, NY.
53

54. 54
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

55. The angular and jagged landscapes
of the Southwest such as at
Monument Valley in Arizona,
indicate an area that was never
55

56. But even the
highest of the
Adirondack
Mountains have
rounded summits
eroded by the
glaciers.
5656

57. 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, 57

58. 58
The courses of both the Niagara River and the Genesee River were changed causing
them to make dramatic new gorges and waterfalls.

59. 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.
59

60. 60
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

61. 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.
6161

62. 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
62
Eskers,
Kames
Till
banks
Changed
stream
channels

63. 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)

64. The Charlotte Whale

65. Camel’s Hump- Roche Moutonnee

66. Lake Willoughby

67. The end.
(until the next Ice Age arrives)
67