1. McKnight's Physical Geography Glacial Modification of Terrain
Chapter 19
Glacial Modification of Terrain
Modified by AJ Allred for Geography 1000
Salt Lake Community College, Fall 2013
Andrew Mercer
Mississippi State University
© 2014 Pearson Education, Inc.

2. Snowpack over years turns to ice.
Ice mass motion under gravity grinds anything in its path.
Glaciation increases erosion rate on a mountain by at least 10 times that of an un-glaciated mountain.

3. Types of Glaciers Continental ice sheets mountain glaciers
Exist in non-mountainous areas
Antarctica and Greenland only two
Outlet glaciers OR
mountain
glaciers

4. Glaciations Past and Present
Glacial ice volume has varied considerably over the last few million years
Evidence left behind allows scientists to determine the chronology of past glaciations
Pleistocene glaciation
Began at least 2.59 million years ago
Last major ice retreat occurred only 9000 years ago
Wisconsin glacial stage marked end
At peak, one-third of total land covered in ice
Most recent “ice age” has advanced and retreated many times, like a bulldozer scraping the earth

5. Glaciations Past and Present
Maximum extent of the Pleistocene glaciation

6. Glaciations Past and Present
Contemporary glaciation
About 10 percent of total Earth land surface still covered by ice
96 percent of the total ice cover is Greenland and Antarctica
Many scattered, small North American glaciers
Mt. Timpanogos (shady side) may still have a small glacier – the last one in Utah?

7. Glaciations Past and Present
Climate change related to contemporary glaciation
Retreating of polar ice caps
Shrinking ice caps an indicator of a warming climate
Antarctic ice shelves breaking
Higher flow rates of outlet glaciers

8. Glacier Formation and Movement
Small variation in global temperature easily changes balance between ice advance and ice retreat
Snow begins as crystallized water vapor
Compresses to granular form
Further compression results in glacial ice
Glacial ice can be thousands
of feet thick

9. Glacier Formation and Movement
Glacier “flow” is orderly sliding of ice molecules
Ice under extreme pressure deforms instead of slipping
Melt water helps glacier to slide along
Flow in response to overlying weight

10. Glacier Formation and Movement
Glacier flow versus glacier advance

11. The Effects of Glaciers
Erosion by glaciers
Volume and speed determine success of glacial erosion
Erosive power of moving ice is greater than that of water
Glacial plucking – picking up of rock material through refreezing of melt-water
Glacial abrasion – bedrock worn down by rock debris inside glacier

12. The Effects of Glaciers
Transportation by glaciers
Glaciers can move large rocks
Typically move sand/silt
Most rock transported along base of the ice
Role of flowing water on moving ice, melt streams
Cracks in ice in which streams run – moulins
[Insert Fig p. 461]

13. The Effects of Glaciers
Deposition by glaciers
Glaciers move rock and soil from one region to another – much U.S. farm soil came from Canada
Till – rock debris deposited by moving or melting ice
Large boulders that are different from surrounding local bedrock, glacial erratics
A glacial erratic

14. The Effects of Glaciers
Deposition by melt water
Large portion of debris carried by glaciers deposited or re-deposited by melt water
Sub-glacial streams from glaciers carry sedimentary material
The Effects of Glaciers

15. Continental Ice Sheets
The “Finger Lakes” of New York state resulted from heavy amounts of ice forming on streams during an ice age. As the “ice age” deepened, ice carved stream beds like “bulldozers”. Later, ice covered the entire region. Only in the last several thousands years has ice retreated enough to expose land for farming and city-building.

16. Continental Ice Sheets
Erosion by ice sheets
Heavy ice can even carve or crush large granite peaks or ‘plutons’
Abrasion on one side – think of scraping like sand paper
“Plucking” on the other side – think of sticking your tongue on a frozen surface and leaving behind some of your skin when you pull away.
Scraping or “abrasion” on the front side
Plucking or pulling off frozen chunks off the back side

17. Continental Ice Sheets
Deposition by Ice Sheets
Moraines – piles of debris left by the glacial “bull dozer”
Pots and kettles – holes in the ground caused by glacier movement and “plucking”
Drumlins – stripes of debris
left along the glacier’s path

18. Minnesota “Land of 10,000 Lakes” [Insert Fig. 19-29 p. 467]
Much of central and northern United States owes farm land to glacial scraping that delivered soil from Canada.
[Insert Fig p. 467]

19. Continental Ice Sheets
Glacier deposited landscape features

20. Mountain Glaciers Mountain glacier development and flow
Usually form in sheltered depressions near heads of stream valleys
Basic landform in glaciated mountains is the cirque, which is a
pocket or scoop mark left
by a glacier moving down
a mountain.
Some cirques reach
all the way to the
bottom of the mountain
cirque

21. Mountain Glaciers
Cirque

22. Mountain Glaciers “U” shaped valley carved by mountain glacier.
Looks just like “Little Cottonwood Canyon”

23. Mountain Glaciers Erosion in the valleys
Some glaciers never leave cirques
Principle erosive work is to deepen, steepen, and widen valleys
U-shaped glacial troughs

24. Mountain Glaciers Deposition by mountain glaciers
Notice the piles of debris left each time the glacier stopped and backed-up

25. Mountain Glaciers
Notice the moraine (debris piles) at the front edge of where a glacier stopped “bulldozing” and retreated.

26. The Periglacial Environment
Much of high-latitude regions are still covered by “permafrost” or “gelisols” that remain frozen or partly frozen.
Earth warming is causing such areas to shrink.
Frozen soils become less stable when they thaw and become soggy.

27. Causes of the Pleistocene Glaciations
The start and stop of “ice ages” may have many causes
Milankovitch cycles – changes in earth “wobble”
Variations in solar output
Variations in carbon dioxide in atmosphere
Changes in continental positions
Atmospheric circulations
Tectonic upheaval – quaking and volcanoes
Are we still in an ice age? <no one really knows>