1. Glaciers and Glaciation
Prepared by Betsy Conklin for
Dr. Isiorho

2. Glaciers
glacier: a large, long-lasting mass of ice, formed on land that moves under the influence of gravity and its own weight
alpine glaciation: found in mountainous regions
continental glaciation: exists where a large part of a continent is covered by glacial ice

3. The Theory of Glacial Ages
theory of glacial ages: states that at times in the past, colder climates prevailed during which much more of the land surface of the earth was glaciated than at present
because the last episode of glaciation was at its peak only about 18,000 years ago, its record has remained largely undestroyed by subsequent erosion and so provides abundant evidence to support the theory

4. Distribution of Glaciers
glaciation is most extensive in polar regions, where little melting takes place at any time of year
presently one-tenth of the land surface is covered by glaciers (compared with about one-third during the peak of the glacial ages)
approximately 85% of the present-day glacier ice is on the Antarctic continent, 10% is in Greenland

5. Types of Glaciers
valley glacier: a glacier that is confined to a valley and flows from a higher to a lower elevation; like streams, small valley glaciers may be tributaries to a larger trunk system
Valley glacier on the flanks of Mount Logan, Canada’s highest mountain

6. Types of Glaciers (cont.)
ice sheet: a mass of ice that is not restricted to a valley but covers a large area of land (over 50,000 square km); Greenland and Antarctica are the only two places on earth to now have ice sheets
ice cap: a glacier covering a relatively small area of land but not restricted to a valley
Diagrammatic cross section of an ice sheet. Vertical scale is highly exaggerated

7. Formation and Growth of Glaciers
A new snowfall may be in the form of light “powder snow,” which consists mostly of air trapped between many six-pointed snowflakes. In a short time the snowflakes settle by compaction under their own weight and much of the air between them is driven out. This eventually forms glacier ice.

8. Formation and Growth of Glaciers (cont.)
ablation\wasted: under the influence of gravity, glacier ice moves downward and is eventually lost or wasted
icebergs: a block of glacier-derived ice floating in water

9. Glacial Budgets
if, over a period of time, the amount of snow a glacier gains is greater than the amount of ice and water it loses, the glacier’s budget is positive if it expands, if the opposite occurs the glacier’s budget is negative
advancing glaciers: glaciers with positive budgets that push outward and downward at their edges
receding glaciers: glaciers with negative budgets that grow smaller and their edges melt back

10. Glacial Budgets (cont.)
zone of accumulation: the upper part of the glacier with a perennial snow cover
zone of wastage: the lower part of the glacier where ice is lost, or wasted, by melting, evaporation, and calving
snow line: the boundary between these two altitudinal zones of a glacier is an irregular line; marks the highest point at which the glacier’s winter snow cover is lost during a melt season
terminus: the lower edge of a glacier which moves farther downvalley when a valley glacier has a positive budget

11. Glacial Budgets (cont.)
A valley glacier as it would appear at the end of a melt season. Below the snow line, glacier ice
and snow have been lost during the melting season. In the zone of accumulation above that line,
firm is added to the glacier from the previous winter fall.

12. Movement of Valley Glaciers
valley glaciers move downslope under the influence of gravity and their own weight, the rate being variable, ranging from less than a few millimeters a day to more than 15 meters a day
glaciers in temperate climates - where the temperature is at or near the melting point for ice - tend to move faster than those in colder regions - where the ice temperature stays well below freezing

13. Movement of Valley Glaciers (cont.)
basal sliding: the sliding of the glacier as a single body over the underlying rock
plastic flow: movement that occurs within the glacier due to the plastic or “deformable” nature of the ice itself
rigid zone: the upper part of the glacier

14. Movement of Valley Glaciers (cont.)
Movement of a glacier. Markers on the glacier indicate the center of the glacier moves
faster than its side. Cross-sectional view shows movement within the glacier.

15. Crevasses
crevasses: open fissures in a glacier caused when the glacier passes over a steep part of the valley floor and moves faster than the upper part of the ridge zone of ice which cannot stretch to move as rapidly as the underlying ice. Being brittle, the ice of the rigid zone is broken by the tensional forces

16. Glacial Erosion faceted: given a flat surface by abrasion
striations: scratches in the rock in the direction of ice movement
rock flour: a powder of fine fragments produced by the grinding of rock across rock
A striated bed rock surface in South Australia

17. Glacial Valleys
u-shaped valley: characteristic cross-profile of a valley carved by glacial erosion
hanging valley: a smaller valley that terminates abruptly high above a main valley
truncated spurs: ridges that have triangular facets produced by glacial erosion at their lower ends
rock-basin lakes (tarns): a lake occupying a depression caused by glacial erosion of bedrock

18. Cirques, Horns, and Artes
cirque: a steep-sided, half-bowl shaped recess carved into a mountain at the head of a glacial valley
horn: the sharp peak that remains after cirques have cut back into a mountain on several sides
arte: sharp ridges that separate adjacent glacially carved valleys

19. Glacial Deposition
till: the unsorted and unlayered rock debris carried or deposited by a glacier
erratic: an ice-transported boulder that has not been derived from the nearby bedrock
Till transported on top of and alongside a glacier in Peru

20. Moraines
moraines: a body of till either being carried on a glacier or left behind after a glacier has receded
lateral moraines: elongate mounds of till which form along the sides of a valley glacier
medial moraine: a single long ridge of till on a glacier, formed by adjacent lateral moraines joining and being carried downglacier
end moraine: a ridge of till piled up along the front edge of a glacier
ground moraine: a blanket of till deposited by a glacier or released as glacier ice melted

21. Moraines (cont.)

22. Outwash outwash: the material deposited by the debris-laden meltwater
drumlins: bodies of till shaped into streamlined hills
esker: a long, sinuous ridge of water-deposited sediment
kettle: a depression caused by the melting of a stagnant block of ice that was surrounded by sediment
Drumlin in New York state
An esker in northeastern Washington

23. Continental Glaciated Terrain
Drumlin in New York state
An esker in northeastern Washington

24. Glacial Lakes and Varves
Varve: two thin layers of sediment, one dark and the other light in color, representing one year’s deposition in a lake
Varves from a former glacial lake. Each pair of light and dark
layers represents a year’s deposition. Gradations on ruler are
centimeters

25. Indirect Effects of Past Glaciation
pluvial lakes: a lake formed during an earlier time of abundant rainfall
fiord: a costal inlet that is a drowned glacially carved valley
tillite: lithified till (evidence of older glaciation comes from rocks called tillites)
A fiord in Alaska

26. Pictures
All pictures used in this power point presentation were taken from the following:
Carlson, Diane H., David McGeary and Charles C. Plummer. Physical Geology: Updated Eighth Edition. New York City, McGraw-Hill Higher Education, 2001.