GLACIERS AND GLACIAL LANDSCAPES
Objectives: In this lab we will examine modern glaciers and look at glaciated landscapes
formed during the last glaciation. Following completion of this lab you should:
1)
2)
3)
4)
understand alpine and continental glaciation,
understand the basic principles of glacier mass balance and equilibrium,
be able to identify common glacial features and glaciated landscapes, and
be able to interpret glacial features on topographic maps, air photos and
LIDAR images.
Key Terms and Concepts:
Continental Glacier
Valley Glacier
Cirque Glacier
Arete
Cirque
Drumlin
Esker
Kettle
Terminus
Zone of Accumulation
Snowline (Firnline)
Calving
Alpine Glacier
Ice Sheet
Tidewater Glacier
Horn
Tarn
Moraine
Outwash Plain
Kettle & Kame Topography
Equilibrium Line
Zone of Ablation
Crevasse
Fjord
Station 1. Mount Rainier (Alpine Glaciation):
Washington is the second most glaciated state in the US. Only Alaska, with over 100,000
glaciers covering 3% of the state, is more glaciated. Glaciers in Washington range in size
from tiny cirque glaciers to larger valley glaciers.
A) Mount Rainier National Park Map
Look at the maps of the Mount Rainier area and examine the alpine glaciers.
1) Examine the contour lines on Carbon Glacier. Notice that they are convex
(bowed downstream) in the lower part of the glacier and concave (bowed
upstream) in the upper part. What do these two areas represent? What is the line
that divides them called?
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2) There are many ways to calculate the ELA of a glacier. Glacial moraines may
be used todetermine the steady state ELA of a glacier, as their deposition is
generally restricted to the ablation zone of a glacier. If moraine preservation is
continuous over time, the presence of lateral moraine may be used to determine
the paleo-ELA of ancient glaciers.
What are some potential problems of using highest elevation of preserved lateral
moraines to determine the paleo-ELA of previously glaciated alpine valleys?
For a modern glacier, the location of the glacier’s terminus, the glacier’s head,
and the surface area of the glacier may all be used to determine the ELA.
a) The toe-to-headwall-altitude ratio method (THAR) uses the head of the glacier
(Ah) and the terminus (At) to determine the ELA. Observations have shown that
for most regions, the ELA lies halfway between the altitude of the head and the
altitude of the terminus of the glacier.
THAR = ELA – At = 0.5
Ah - At
Calculate the ELA for Carbon Glacier and the Tahoma Glacier using the THAR
method. Is the ELA the same or different for both glaciers? Is THAR a reliable
method, why or why not? What factors does this method not account for?
3) Estimate the surface slope of Carbon Glacier.
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B) Mount Rainier aerial photo
1) Look at Carbon Glacier. How do crevasses appear? What do crevasses
indicate about the underlying topography?
2) Look at some of the outwash streams flowing from the glaciers. Would you
describe them as meandering or braided? What properties of glacially derived
meltwater streams might explain this drainage pattern?
C) Crillion Glacier Air Photo
Look air photo #6. This glacier is different than any you have seen so far. It is
called a tidewater glacier, because it terminates in the ocean and calves icebergs into the
sea. Empirical studies indicate that the calving rate of a tidewater glacier is partly
controlled by the depth of the water at the glacier terminus.
1) How do you think calving affects glacier equilibrium and mass balance (think
about how non-calving glaciers lose mass versus calving glaciers)?
2) Propose a theory to explain how a calving glacier might advance (i.e., how can
the glacier change the amount of ice lost to calving? What conditions at the base
of a calving glacier might stabilize it?).
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Station 2. North Cascades National Park (Alpine Glaciation):
The North Cascades were covered with extensive alpine glaciers during the last
glaciation. Today, the North Cascades hold about half of all the glaciers in the
continental US.
A) North Cascades National Park (National Park Map)
1) Look at the modern glaciers. Do the glaciers tend to be oriented in one
direction? If so, what direction and why do you think this occurs?
2) What topographic differences exist between landscapes affected by alpine
glaciation and landscapes affected by continental glaciation? Why?
3) Looking at the topography of the North Cascades, which type of glaciation do
you think occurred there? List three or more erosional features that indicate this
type of glaciation.
4) Temperatures in Alaska were cold enough to support glaciers during the last
ice age, so why did a large part of Alaska remain unglaciated?
B) Wyoming
1) Look at the air photo #9. What are the predominant glacial features in this
photo?
2) How do these features form?
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Station 3. WASHINGTON (Alpine and Continental Glaciers):
During the last glaciation northern Washington was covered with enormous ice sheets
which accumulated in British Columbia and flowed into the Fraser and Okanogan River
valleys into northern Washington. An extensive system of glaciers also existed in the
valleys of the Cascades and Olympics, which extended down into the Puget Lowland. As
climate changed these glaciers retreated until they covered only the highest peaks of the
range. Although these glaciers have been predominantly retreating since 15,000 years
ago, some periods of readvance have occurred. Using your knowledge of glaciers and the
maps provided, answer the following questions.
A) Olympic Mountains and the North Cascades (National Park Maps)
1) Look at the topographic sheet for Olympic National Park and find the glaciers
on Mt. Olympus. Which side of Mt. Olympus supports the largest and most extensive
glaciers? Provide at least two reasons why you think this occurs.
2) Now look at the terminus of the most extensive glaciers on Mt. Olympus.
What is the elevation? Compare this with the average terminus elevation of glaciers in
the North Cascades. Which is lower? Why? Note that the two national park maps are in
different scales; one in feet the other in meters (1 meter is approximately 3.3 feet).
3) Look again to the Olympic National Park map. Study the northern boundary
of the map and see if you can determine the thickness of the Juan de Fuca lobe of the
Cordilleran ice sheet was during the last ice glaciation. To do this you need to use the
Olympic Mountains as a "dipstick" and determine how deeply the mountain range was
"submerged" in ice. (Remember, the ice sheet would have covered peaks and rounded
then off, whereas those areas not covered by the ice sheet would retain their sharp horns
and arêtes).
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B) Mt Rainier (National Park Map and Photo #5)
1) Find the Carbon Glacier on the NW side of Mt. Rainier. Give three reasons
why the Carbon Glacier reaches the lowest elevation of all the glaciers on Mt. Rainier
(two of these reasons you should already be familiar with).
2) Now look at the air photo of the Carbon Glacier (#5). Find the snowline, or
firnline, on the glacier. Using the photo and the topographic map determine the elevation
of the snowline. If this picture was taken at the very end of the summer, what would this
line represent?
3) What would happen to Carbon Glacier if the snowline dropped 100 feet?
C) Puget Lowland (LIDAR and DEM composite)
1) What features (both depositional and erosional) might you look for in
Northern Washington to determine how far the continental ice sheets extended during the
last ice glaciation? (i.e. What sort of features define a glaciated landscape?)
2) Examine the topography. Are landforms oriented in a specific direction? If
so, what is their orientation and what geomorphic agent (ice, water, wind, etc.) created
them?
D) Whidbey Island (LIDAR imagery and 7.5 minute topographic maps)
Look at the Coupeville 7.5 minute topographic map. Find the topographic depressions
located directly northwest of Penn Cove on the topographic map and the Lidar image.
Some of these depressions intersect the water table and form lakes.
1) How do you think these topographic depressions formed?
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2) Where did the Puget Lobe ice sheet terminate when the sediment was deposited in
which the kettle depressions occupy?
If you look south of the town of Coupeville you will observe two prairies (Ebey and
Smith Prairies) that have flat surface topography. Find these same features on the
LIDAR imagery. If you look very close at LIDAR image you will observe faint, braided
channels on the surface of these features. The planar features located south of the town
of Coupeville look very similar to the surfaces of modern deltas (see figure below).
3) If the planar features located south of Coupeville are truly deltas, how might you
reconcile the fact that their braided surfaces lie above modern sea level?
4) What is the modern elevation of Ebey and Smith Prairies (feet above sea level) and
what does this tell you about the elevation of relative sea level at the time that these
deltaic features formed?
5) Since there is no existing stream or high topography to serve as source for these deltas,
how and when do you think they formed?
6) Do you think that the sediment that comprises the deltas is much older, similar in age
or much younger, than the sediment that the kettle depressions occupy northwest of Penn
Cove?
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Station 5. THE NORTHEAST:
Although no glaciers presently exist in the Northeastern U.S., the region was covered
with a mile thick ice sheet less than 20,000 years ago. At that time the Laurentide ice
sheet extended down from Canada and reached a maximum position in Northern
Pennsylvania and on the continental shelf off what is now New England. However, as in
Washington, the glaciers left evidence of their passing.
Greenland
Ice Sheet
Cordilleran
Ice Sheet
Laurentide
Ice Sheet
A) Maximum Extent of the Laurentide Ice Sheet
Look at the reconstruction of the Laurentide Ice Sheet shown above. The
maximum extent of the ice sheets during the last glaciation is outlined. Based on this
reconstruction explain what glacial feature Long Island, Martha's Vineyard, and
Nantucket represent (they are located along the coastline of New York and
Massachusetts).
B) Palmyra, New York
This is a map of the famous drumlin fields located near Syracuse, New York.
How are the drumlins oriented related to paleo-ice flow direction? Drumlins are
asymmetrical. Which side is steeper (the upglacier or downglacier side)?
C) Eastern Greenland
Examine the Greenland topographic map. Many alpine glaciers are still present
here, but has this coast been glaciated by larger ice masses? How can you tell?
Construct a cross-section of the Ikaasaalap llinnera valley (37° 30’ W, 66° N). What
other glacial erosion features do you see on this map?
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Map Needs
Olympic National Park (topographic map) 5 copies
North Cascades National Park (topographic map) 5 copies
Mount Rainier (topographic map) 5 copies
Puget Lowland (composite LIDAR and DEM) 5 copies
Whidbey Island Lidar 5 copies
Coupeville 7.5 minute quadrangle map (3 copies)
Aerial Photographs
Mt. Rainier
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