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.

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.

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

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

Glaciations Past and Present Maximum extent of the Pleistocene glaciation

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?

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

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

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

Glacier Formation and Movement Glacier flow versus glacier advance

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

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. 19-16 p. 461]

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

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

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.

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

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

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. 19-29 p. 467]

Continental Ice Sheets Glacier deposited landscape features

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

Mountain Glaciers Cirque

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

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

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

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

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.

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>