Glaciers and GlaciationGlaciers and Glaciation

Prepared by Betsy Conklin forPrepared by Betsy Conklin for

Dr. IsiorhoDr. Isiorho

GlaciersGlaciers glacier: a large, long-lasting mass of glacier: a large, long-lasting mass of

ice, formed on land that moves under ice, formed on land that moves under the influence of gravity and its own the influence of gravity and its own weightweight

alpine glaciation: found in alpine glaciation: found in mountainous regionsmountainous regions

continental glaciation: exists where a continental glaciation: exists where a large part of a continent is covered by large part of a continent is covered by glacial iceglacial ice

The Theory of Glacial AgesThe Theory of Glacial Ages theory of glacial ages: states that at times in theory of glacial ages: states that at times in

the past, colder climates prevailed during the past, colder climates prevailed during which much more of the land surface of the which much more of the land surface of the earth was glaciated than at present earth was glaciated than at present

because the last episode of glaciation was at because the last episode of glaciation was at its peak only about 18,000 years ago, its its peak only about 18,000 years ago, its record has remained largely undestroyed by record has remained largely undestroyed by subsequent erosion and so provides subsequent erosion and so provides abundant evidence to support the theoryabundant evidence to support the theory

Distribution of GlaciersDistribution of Glaciers glaciation is most extensive in polar glaciation is most extensive in polar

regions, where little melting takes place at regions, where little melting takes place at any time of yearany time of year

presently one-tenth of the land surface is presently one-tenth of the land surface is covered by glaciers (compared with about covered by glaciers (compared with about one-third during the peak of the glacial one-third during the peak of the glacial ages)ages)

approximately 85% of the present-day approximately 85% of the present-day glacier ice is on the Antarctic continent, glacier ice is on the Antarctic continent, 10% is in Greenland10% is in Greenland

Types of GlaciersTypes of Glaciers valley glacier: a glacier that is valley glacier: a glacier that is

confined to a valley and flows from confined to a valley and flows from a higher to a lower elevation; like a higher to a lower elevation; like streams, small valley glaciers may streams, small valley glaciers may be tributaries to a larger trunk be tributaries to a larger trunk systemsystem

Valley glacier on the flanks of Mount Logan, Canada’s highest mountainValley glacier on the flanks of Mount Logan, Canada’s highest mountain

Types of Glaciers (cont.)Types of Glaciers (cont.) ice sheet: a mass of ice that is not ice sheet: a mass of ice that is not

restricted to a valley but covers a large restricted to a valley but covers a large area of land (over 50,000 square km); area of land (over 50,000 square km); Greenland and Antarctica are the only Greenland and Antarctica are the only two places on earth to now have ice two places on earth to now have ice sheetssheets

ice cap: a glacier covering a relatively ice cap: a glacier covering a relatively small area of land but not restricted to a small area of land but not restricted to a valleyvalley

Diagrammatic cross section of an ice sheet. Vertical scale is highly exaggeratedDiagrammatic cross section of an ice sheet. Vertical scale is highly exaggerated

Formation and Growth of Formation and Growth of GlaciersGlaciers

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

Formation and Growth of Formation and Growth of Glaciers (cont.)Glaciers (cont.)

ablation\wasted: under the ablation\wasted: under the influence of gravity, glacier ice influence of gravity, glacier ice moves downward and is eventually moves downward and is eventually lost or wastedlost or wasted

icebergs: a block of glacier-derived icebergs: a block of glacier-derived ice floating in waterice floating in water

Glacial BudgetsGlacial Budgets if, over a period of time, the amount of snow a if, over a period of time, the amount of snow a

glacier gains is greater than the amount of ice glacier gains is greater than the amount of ice and water it loses, the glacier’s budget is and water it loses, the glacier’s budget is positivepositive if it expands, if the opposite occurs the if it expands, if the opposite occurs the glacier’s budget is glacier’s budget is negativenegative

advancing glaciers: glaciers with positive advancing glaciers: glaciers with positive budgets that push outward and downward at budgets that push outward and downward at their edgestheir edges

receding glaciers: glaciers with negative receding glaciers: glaciers with negative budgets that grow smaller and their edges melt budgets that grow smaller and their edges melt back back

Glacial Budgets (cont.)Glacial Budgets (cont.) zone of accumulation: the upper part of the glacier zone of accumulation: the upper part of the glacier

with a perennial snow coverwith a perennial snow cover zone of wastage: the lower part of the glacier where zone of wastage: the lower part of the glacier where

ice is lost, or wasted, by melting, evaporation, and ice is lost, or wasted, by melting, evaporation, and calvingcalving

snow line: the boundary between these two snow line: the boundary between these two altitudinal zones of a glacier is an irregular line; altitudinal zones of a glacier is an irregular line; marks the highest point at which the glacier’s winter marks the highest point at which the glacier’s winter snow cover is lost during a melt seasonsnow cover is lost during a melt season

terminus: the lower edge of a glacier which moves terminus: the lower edge of a glacier which moves farther downvalley when a valley glacier has a farther downvalley when a valley glacier has a positive budgetpositive budget

Glacial Budgets (cont.)Glacial Budgets (cont.)

A valley glacier as it would appear at the end of a melt season. Below the snow line, glacier ice 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,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.firm is added to the glacier from the previous winter fall.

Movement of Valley Movement of Valley GlaciersGlaciers

valley glaciers move downslope under the valley glaciers move downslope under the influence of gravity and their own weight, influence of gravity and their own weight, the rate being variable, ranging from less the rate being variable, ranging from less than a few millimeters a day to more than than a few millimeters a day to more than 15 meters a day15 meters a day

glaciers in temperate climates - where the glaciers in temperate climates - where the temperature is at or near the melting point temperature is at or near the melting point for ice - tend to move faster than those in for ice - tend to move faster than those in colder regions - where the ice temperature colder regions - where the ice temperature stays well below freezingstays well below freezing

Movement of Valley Movement of Valley Glaciers (cont.)Glaciers (cont.)

basal sliding: the sliding of the glacier basal sliding: the sliding of the glacier as a single body over the underlying as a single body over the underlying rockrock

plastic flow: movement that occurs plastic flow: movement that occurs within the glacier due to the plastic or within the glacier due to the plastic or “deformable” nature of the ice itself“deformable” nature of the ice itself

rigid zone: the upper part of the rigid zone: the upper part of the glacierglacier

Movement of Valley Movement of Valley Glaciers (cont.)Glaciers (cont.)

Movement of a glacier. Markers on the glacier indicate the center of the glacier movesMovement 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.faster than its side. Cross-sectional view shows movement within the glacier.

CrevassesCrevasses crevasses: open fissures in a glacier crevasses: open fissures in a glacier

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

Glacial ErosionGlacial Erosion faceted: given a flat surface by faceted: given a flat surface by

abrasionabrasion striations: scratches in the rock in striations: scratches in the rock in

the direction of ice movementthe direction of ice movement rock flour: a powder of fine rock flour: a powder of fine

fragments produced by the fragments produced by the grinding of rock across rock grinding of rock across rock

A striated bed rock surface in South AustraliaA striated bed rock surface in South Australia

Glacial ValleysGlacial Valleys u-shaped valley: characteristic cross-profile of u-shaped valley: characteristic cross-profile of

a valley carved by glacial erosiona valley carved by glacial erosion hanging valley: a smaller valley that hanging valley: a smaller valley that

terminates abruptly high above a main valleyterminates abruptly high above a main valley truncated spurs: ridges that have triangular truncated spurs: ridges that have triangular

facets produced by glacial erosion at their facets produced by glacial erosion at their lower endslower ends

rock-basin lakes (tarns): a lake occupying a rock-basin lakes (tarns): a lake occupying a depression caused by glacial erosion of depression caused by glacial erosion of bedrockbedrock

Cirques, Horns, and ArCirques, Horns, and Artestes cirque: a steep-sided, half-bowl shaped cirque: a steep-sided, half-bowl shaped

recess carved into a mountain at the head recess carved into a mountain at the head of a glacial valleyof a glacial valley

horn: the sharp peak that remains after horn: the sharp peak that remains after cirques have cut back into a mountain on cirques have cut back into a mountain on several sidesseveral sides

ararte: sharp ridges that separate adjacent te: sharp ridges that separate adjacent glacially carved valleysglacially carved valleys

Glacial DepositionGlacial Deposition till: the unsorted and unlayered till: the unsorted and unlayered

rock debris carried or deposited by rock debris carried or deposited by a glaciera glacier

erratic: an ice-transported boulder erratic: an ice-transported boulder that has not been derived from the that has not been derived from the nearby bedrocknearby bedrock

Till transported on top of and alongside a glacier in PeruTill transported on top of and alongside a glacier in Peru

MorainesMoraines moraines: a body of till either being carried on a moraines: a body of till either being carried on a

glacier or left behind after a glacier has recededglacier or left behind after a glacier has receded lateral moraines: elongate mounds of till which lateral moraines: elongate mounds of till which

form along the sides of a valley glacierform along the sides of a valley glacier medial moraine: a single long ridge of till on a medial moraine: a single long ridge of till on a

glacier, formed by adjacent lateral moraines glacier, formed by adjacent lateral moraines joining and being carried downglacierjoining and being carried downglacier

end moraine: a ridge of till piled up along the front end moraine: a ridge of till piled up along the front edge of a glacieredge of a glacier

ground moraine: a blanket of till deposited by a ground moraine: a blanket of till deposited by a glacier or released as glacier ice meltedglacier or released as glacier ice melted

Moraines (cont.)Moraines (cont.)

OutwashOutwash outwash: the material deposited by the outwash: the material deposited by the

debris-laden meltwaterdebris-laden meltwater drumlins: bodies of till shaped into drumlins: bodies of till shaped into

streamlined hillsstreamlined hills esker: a long, sinuous ridge of water-esker: a long, sinuous ridge of water-

deposited sedimentdeposited sediment kettle: a depression caused by the melting kettle: a depression caused by the melting

of a stagnant block of ice that was of a stagnant block of ice that was surrounded by sedimentsurrounded by sediment

Drumlin in New York stateDrumlin in New York state An esker in northeastern WashingtonAn esker in northeastern Washington

Continental Glaciated Continental Glaciated TerrainTerrain

Drumlin in New York stateDrumlin in New York state An esker in northeastern WashingtonAn esker in northeastern Washington

Glacial Lakes and VarvesGlacial Lakes and Varves Varve: two thin layers of sediment, Varve: two thin layers of sediment,

one dark and the other light in one dark and the other light in color, representing one year’s color, representing one year’s deposition in a lakedeposition in a lake

Varves from a former glacial lake. Each pair of light and darkVarves from a former glacial lake. Each pair of light and darklayers represents a year’s deposition. Gradations on ruler arelayers represents a year’s deposition. Gradations on ruler arecentimeterscentimeters

Indirect Effects of Past Indirect Effects of Past GlaciationGlaciation

pluvial lakes: a lake formed during pluvial lakes: a lake formed during an earlier time of abundant rainfallan earlier time of abundant rainfall

fiord: a costal inlet that is a fiord: a costal inlet that is a drowned glacially carved valleydrowned glacially carved valley

tillite: lithified till (evidence of tillite: lithified till (evidence of older glaciation comes from rocks older glaciation comes from rocks called tillites)called tillites)

A fiord in AlaskaA fiord in Alaska

PicturesPictures

All pictures used in this power point presentation were All pictures used in this power point presentation were taken from the following:taken from the following:

Carlson, Diane H., David McGeary and Charles C. Carlson, Diane H., David McGeary and Charles C. Plummer. Plummer. Physical Geology: Updated Eighth EditionPhysical Geology: Updated Eighth Edition. . New York City, McGraw-Hill Higher Education, 2001.New York City, McGraw-Hill Higher Education, 2001.