Chapter 6: Glaciers, Deserts, and Winds

Glacier

A thick mass of ice originating on land from the compaction and recrystallization of snow that shows evidence of past or present flow.

Last Glacial Maximum

About 18,000 years ago, glacial ice not only covered Greenland and Antarctica but also covered large portions of North America, Europe, and Siberia

Valley (alpine) glacier

A glacier confined to a mountain valley, which in most instances had previously been a stream valley.

Ice sheet

A very large, thick mass of glacial ice flowing outward in all directions from one or more accumulation centers

Sea ice

Frozen seawater that is associated with polar regions. The area covered by sea ice expands in winter and shrinks in summer.

Ice shelf

A large, relatively flat mass of floating ice that forms where glacial ice flows into bays and extends seaward from the coast but remains attached to the land along one or more sides

Ice cap

A mass of glacial ice covering a high upland or plateau and spreading out radially.

Piedmont glacier

A glacier that forms when one or more valley glaciers emerge from the confining walls of mountain valleys and spread out to create a broad sheet in the lowlands at the base of the mountains.

Outlet glacier

A tongue of ice that normally flows rapidly outward from an ice cap or ice sheet, usually through mountainous terrain to the sea

Zone of fracture

The upper portion of a glacier, consisting of brittle ice.

Crevasse

A deep crack in the brittle surface of a glacier.

Zone of accumulation

The part of a glacier characterized by snow accumulation and ice formation. Its outer limit is the snowline

Zone of wastage

The part of a glacier beyond the zone of accumulation where all of the snow from the previous winter melts, as does some of the glacial ice.

Calving

Wastage of a glacier that occurs when large pieces of ice break off into water.

Iceberg

A mass of floating ice produced by a calving glacier. Usually 20 percent or less of it protrudes above the waterline

Glacial budget

The balance, or lack of balance, between ice formation at the upper end of a glacier and ice loss in the zone of wastage.

Plucking

The process by which pieces of bedrock are lifted out of place by a glacier.

Abrasion

The grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, or ice.

(1) rate of glacial movement; (2) thickness of the ice; (3) shape, abundance, and hardness of the rock fragments contained in the ice at the base of the glacier; and (4) erodibility of the surface beneath the glacier.

4 Factors that controlled Glacial Erosion

Rock flour

Ground-up rock produced by the grinding effectof a glacier

Glacial striations

Scratches and grooves on bedrock caused by glacial abrasion

Glacial trough

A valley that has been widened and deepened by the erosive action of a glacier. It has relatively straight, flat-bottomed, deeper, and steep-sided valley formed by glacial erosion.

Hanging Valley

A tributary valley that enters a glacial trough at a considerable height above its floor.

Cirque

An amphitheater-shaped basin at the head of a glaciated valley produced by frost wedging and plucking

Tarn

A small mountain lake, especially one set in a glaciated steep-walled amphitheatre known as a cirque

Arete

A narrow knifelike ridge separating two adjacent glaciated valleys.

Horn

A pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit.

Fiord

A steep-sided inlet of the sea formed when a glacial trough was partially submerged.

Glacial drift

An all-embracing term for sediments of glacial origin, no matter how, where, or in what shape they were deposited. Also known simply as drift.

Till

Unsorted sediment deposited directly by a glacier.

Stratified drift

Sediments deposited by glacial meltwater

Glacial erratic

An ice-transported boulder that was notderived from bedrock near its present site

Lateral moraine

A ridge of till along the sides of an alpine glacier composed primarily of debris that fell to the glacier from the valley walls.

Medial moraine

A ridge of till formed when lateralmoraines from two coalescing alpine glaciers join.

End moraine

A ridge of till marking a former position of the front of a glacier.

Ground moraine

An undulating layer of till deposited as the ice front retreats.

Outwash plain

A relatively flat, gently sloping plain consisting of materials deposited by meltwater streams in front of the margin of an ice sheet.

Valley train

A relatively narrow body of stratified drift deposited on a valley floor by meltwater streams that issue from a valley glacier.

Kettle

Depressions created when blocks of ice became lodged in glacial deposits and subsequently melted.

Drumlin

A streamlined asymmetrical hill composed of glacial till. The steep side of the hill faces the direction from which the ice advanced.

Esker

A sinuous ridge composed largely of sand and gravel deposited by a stream flowing in a tunnel beneath a glacier near its terminus.

Kame

A steep-sided hill composed of sand and gravel that originates when sediment is collected in openings in stagnant glacial ice.

Proglacial lake

A lake created when a glacier acts as a dam, blocking the flow of a river or trapping glacial meltwater. The term refers to the position of such lakes just beyond the outer limits of a glacier

Pluvial lake

A lake formed during a period of increased rainfall. During the Pleistocene epoch, this occurred in some non glaciated regions during periods of ice advance elsewhere.

Quaternary period

The most recent period on the geologic time scale. It began about 2.6 million years ago and extends to the present.

Plate Tectonics, Variation in Earth's Orbit, Greenhouse gases, and Ocean currents

Causes of Ice Ages

Dry climate

A climate in which yearly precipitation is not as great as the potential loss of water by evaporation.

Desert

One of the two types of dry climate; the driest of the dry climates.

Steppe

One of the two types of dry climate. A marginal and more humid variant of the desert that separates it from bordering humid climates.

Ephemeral stream

A stream that is usually dry because it carries water only in response to specific episodes of rainfall. Most desert streams are of this type.

Interior drainage

A discontinuous pattern of intermittent streams that do not flow to the ocean.

Alluvial fan

A fan-shaped deposit of sediment formed when a stream's slope is abruptly reduced.

Bajada

An apron of sediment along a mountain front created by the coalescence of alluvial fans.

Playa lake

A temporary lake in a desert.

Playa

A flat area on the floor of an undrained desert basin. Following heavy rain, this becomes a lake.

Deflation

The lifting and removal of loose material by wind.

Blowout

A depression excavated by the wind in easily eroded deposits.

Desert pavement

A layer of coarse pebbles and gravel created when wind removed the finer material.

Loess

Deposits of windblown silt, lacking visible layers, generally buff-colored, and capable of maintaining a nearly vertical cliff.

Dune

A hill or ridge of wind-deposited sand

Slip face

The steep, leeward slope of a sand dune; it maintains an angle of about 34 degrees.

Star dunes

An isolated hill of sand that exhibits a complex form and develops where wind directions are variable.

Cross bedding

A structure in which relatively thin layers are inclined at an angle to the main bedding. Formed by currents of wind or water.

Barchan dunes

A solitary sand dune shaped like a crescent with its tips pointing downward.

Transverse dunes

A series of long ridges oriented at right angles to the prevailing wind; these dunes form where vegetation is sparse and sand is very plentiful.

Barchanoid dunes

Dunes forming scalloped rows of sand oriented at right angles to the wind. This form is intermediate between isolated barchans and extensive waves of transverse dunes.

Longitudinal dunes

Long ridges of sand are oriented parallel to the prevailing wind; these dunes form where sand supplies are limited.

Parabolic dunes

Dunes that resemble barchans, except that their tips point into the wind; they often form along coasts that have strong onshore winds, abundant sand, and vegetation that partly covers the sand.