I. Origin of Glaciers

II. Types of Glaciers

III. The Ice Front

IV. Tools of Glacial Erosion

V. Features Produced by Glacial Erosion

VI. Features Produced by Glacial Deposition

VII. The Most Recent Ice Age

VIII. Effects of the Pleistocene Ice Age

IX. Possible Essay Questions

X. Practice Questions

• Definition - any mass of solid ice that is moving (flowing) is called a glacier.

• Whenever the amount of snowfall exceeds the amount of melting, snow will start to accumulate to great depth.
• As overburden pressure in the snowfield increases, snowflakes are recrystallized (metamorphosed) into granular ice (firn).
• Continued pressure increase causes the ice crystals to become aligned and to change from granular to solid ice (ice schist).
• Alignment of the crystals allows the ice to move (flow) plastically.

Back to Top

II. Types of Glaciers - There are only two types of glaciers in the world

• Valley (alpine) glaciers -

• Most of the world's glaciers are valley glaciers, which flow down valleys under the influence of gravity (like molasses flows slowly down an inclined channel).

• Continental glaciers -

• Continental glaciers flow radially outward from a center of extreme thickness (like molasses poured on a table top spreads slowly outward in all directions).
• Greenland and Antarctica are covered with the only two continental glaciers remaining in the world today.

Back to Top

• Determined by rate of snow accumulation in relation to rate of melting. That part of the glacier where accumulation exceeds melting is called the zone of accumulation. That part of the glacier where melting exceeds accumulation is called the zone of melting (ablation). The ice front will remain in the same place as long as the rate of accumulation is equal to the rate of melting.
• If climatic change causes accumulation to increase, the ice front will advance until the rate of melting once again equals the rate of accumulation
• If climatic change causes accumulation to decrease, the ice front will retreat (melt back up the valley) until the rate of melting once again equals the rate of accumulation

• Remember that the glacier ice is always physically moving downhill in valley glaciers or outward in continental glaciers, regardless of whether the ice front is advancing or retreating.

• Crevasses -

• The top surface of flowing ice is brittle because it is under less pressure, hence contains many fractures (crevasses), especially in places where the gradient increases.

Back to Top

• Glaciers pluck pieces of bedrock from their bottom (and from the sidewalls and headwalls of valley glaciers) by alternate freezing and thawing action. Other rocks fall onto the surface of the glacier from the surrounding mountains and melt their way down to the bottom.
• These rocks (the load of the glacier), which are dragged along in the moving ice, scrape and abrade the land under the glacier, thus eroding it away.
• After the glacier melts, the exposed rock surface will be grooved, scratched, and polished as a result of the passage of the overriding ice and gravel particles.

Back to Top

• U-shaped valley - a wide, flat-bottomed valley with steep sides that is created because most of the glacial load is carried along the sides of the glacier, so maximum glacial erosion occurs along the sides.
• Cirque - a bowl-shaped amphitheater eroded by the head of a glacier.
• Arˆte - a sharp, narrow ridge between adjacent glacial valleys or cirques.
• Glacial horn - a steep mountain that has cirques on three or more sides.
• Hanging valley - a small glacial valley that is tributary to and drops steeply into a major glacial valley.
• Rock basin lake - a water-filled depression within the glacial valley that was carved out of the bedrock by a glacier that for a short distance was actually moving uphill.
• Fiord (fjord) - a glacial valley that has been eroded below sea level so that the ocean fills the valley when the glacier melts.

Back to Top

• Glacial Till - material carried by the glacier is left behind when the glacier melts. It is unsorted- ther are both large and small grains mixed together.
• Loess - Silt that has been blown off a glacier by the wind and deposited downwind.
• Erratic - a large rock that has been carried a great distance by a glacier and left in an isolated position.
• Moraine - a pile of gravel, sand, and mud that has been left at the front or side of the glacier.
• Esker - a subglacial stream fills its tunnel with sediment; when the glacier melts, an elongate, sinuous ridge of sediment is left behind.
• Kettle - a large, slow-melting block of ice becomes separated from the main body of the glacier during the melting process and is surrounded by sediment washed from the glacier; when the ice melts, a depression is left where the ice used to be.

Back to Top

• Occurred during the latest 2,000,000 years of geologic time, during a period called the Pleistocene Epoch.
• For portions of the Pleistocene Epoch, northern Europe, northern Asia (Siberia), and northern North America (almost all of Canada) were covered by large, continental glaciers.
• Four major advances and retreats of the ice are recorded by Pleistocene glacial deposits.
• We are presently in an interglacial time (sometime in the middle of the fourth major retreat), but our historical weather records are so short that we don't know if we are still coming out of the last glacial time (getting warmer) or are starting to enter into a new glacial time (getting cooler).

Back to Top

• The flat, lake-covered topography of eastern Canada and northeastern United States is the result of erosion and deposition by the Pleistocene continental glaciation.
• The Missouri River, which used to flow north, was diverted and forced to join the Mississippi River.
• Water that was needed to make the glacial ice that formed the large, continental glaciers came from the ocean, so sea level was lowered over 400 feet; Alaska and Siberia were joined, as were England and France, and the East Coast was 60 miles farther east.
• Climate was cooler and wetter during glacial advances; most western United States dry lakes were full of water at the time.

 Back to Top

Back to Top

X. Practice Questions

Back to Index