Glaciers, Deserts, and Wind

Glacier

A thick mass of ice that forms on land from the compaction and recrystallization of snow and moves slowly under its own weight.

Valley (alpine) glacier

A glacier that forms in a mountainous area and flows down preexisting valleys, often following stream courses.

Ice sheet

A massive, continental-scale glacier covering more than 50,000 square kilometers, such as those in Antarctica and Greenland.

Sea ice

Frozen ocean water that forms, grows, and melts in the ocean, distinct from icebergs or glaciers.

Ice shelf

A thick, floating extension of glacial ice that projects from land out over the ocean while still attached to the glacier.

Ice cap

A mass of glacial ice that covers less than 50,000 square kilometers and buries the underlying landscape. (Think Ice Sheet but smaller)

Piedmont glacier

A glacier that forms when valley glaciers spill out onto flat plains, spreading into bulb-like lobes.

Outlet glacier

A tongue of ice that extends outward from an ice cap or ice sheet, often channeled by mountain valleys.

Zone of fracture

The upper brittle layer of a glacier that breaks rather than flows, forming cracks called crevasses.

Crevasse

A deep, open crack in the brittle surface of a glacier caused by movement over uneven terrain.

Zone of accumulation

The area of a glacier where snowfall exceeds melting, causing ice to build up.

Snowline (equilibrium line)

The boundary on a glacier separating the zone of accumulation above from the zone of wastage below.

Zone of wastage

The lower part of a glacier where ice loss from melting, sublimation, or calving exceeds accumulation.

Calving

The process by which large chunks of ice break off the end of a glacier to form icebergs.

Iceberg

A large mass of floating ice that has broken off from a glacier or ice shelf and drifts in the ocean.

Glacial budget

The balance between ice accumulation and ice loss in a glacier; it determines whether the glacier advances or retreats.

Plucking

A process by which a glacier lifts and removes blocks of rock from the bedrock beneath it.

Abrasion

The scraping and smoothing of bedrock by rocks and debris embedded in moving glacier ice.

Rock flour

Finely ground rock produced by glacial abrasion, often giving meltwater a cloudy or milky appearance.

Glacial striations

Long, parallel scratches or grooves in bedrock caused by rocks embedded in a moving glacier.

Glacial trough

A U-shaped valley formed by the erosive action of a valley glacier.

Hanging valley

A smaller glacial valley that joins a deeper main valley, often forming waterfalls.

Cirque

A bowl-shaped, amphitheater-like depression at the head of a glacier valley formed by erosion.

Arête

A sharp ridge that forms between two adjacent glacial valleys or cirques.

Horn

A sharp, pyramid-like peak formed where several cirques erode a mountain from different sides.

Fiord

A deep, glacially carved valley now flooded by the sea.

Glacial drift

All sediment of glacial origin, including both unstratified till and stratified drift.

Till

Unsorted glacial sediment deposited directly by melting ice.

Glacial erratic

A large boulder transported and deposited by a glacier, often resting far from its source region.

Stratified drift

Glacial sediment that has been sorted and layered by meltwater streams.

Lateral moraine

A ridge of till deposited along the sides of a valley glacier.

Medial moraine

A ridge of till formed where two valley glaciers merge, combining their lateral moraines.

End moraine

A ridge of till deposited at the farthest advance or stationary margin of a glacier.

Ground moraine

A layer of till deposited beneath a glacier as it retreats, forming a gently rolling landscape.

Outwash plain

A broad, flat area formed by meltwater streams depositing stratified drift beyond the glacier’s end moraine.

Valley train

A long, narrow deposit of stratified drift confined to a valley downstream from a glacier.

Kettle

A depression formed when a buried block of ice melts, often filling with water to become a kettle lake.

Drumlin

A streamlined hill composed of till, shaped by glacial ice movement, with a steep up-ice side and gentle down-ice slope.

Esker

A long, winding ridge of stratified sand and gravel deposited by meltwater streams beneath a glacier.

Kame

A steep-sided hill of sand and gravel formed by sediment deposition in a meltwater cavity or depression.

Proglacial lake

A lake that forms in front of a glacier, often dammed by ice or glacial deposits.

Pluvial lake

A lake formed during periods of increased rainfall and cooler climate, often during glacial periods.

Quaternary period

The most recent geologic period, spanning the last 2.6 million years, marked by repeated glaciations.

Dry climate

A climate in which precipitation is low and evaporation exceeds rainfall, leading to arid or semi-arid conditions.

Desert

A region that receives less than 25 centimeters (10 inches) of precipitation per year and has sparse vegetation.

Steppe

A semi-arid region receiving slightly more precipitation than a desert, supporting grasslands.

Ephemeral stream

A stream that flows only after rainfall and remains dry most of the time.

Interior drainage

A drainage pattern where water flows into basins or depressions and does not reach the ocean.

Alluvial fan

A cone-shaped deposit of sediment formed where a stream emerges from a mountain canyon onto a flat plain.

Bajada

A broad, gently sloping surface formed by the merging of adjacent alluvial fans along a mountain front.

Playa lake

A temporary shallow lake that forms in a desert basin during periods of heavy rain.

Deflation

The removal of fine sediment by wind, leaving behind coarser material.

Blowout

A shallow depression formed by wind erosion in sandy or loosely consolidated material.

Desert pavement

A surface of closely packed pebbles and stones left behind after wind removes finer material.

Loess

Wind-deposited silt and clay, often forming fertile, fine-grained soils.

Dune

A mound or ridge of sand formed by wind deposition.

Slip face

The steep, leeward side of a dune where sand accumulates and slides down.

Cross bed

Slanted layers of sand within a dune, formed by wind shifting and depositing sand on the slip face.

Barchan dunes

Crescent-shaped dunes with tips pointing downwind, formed in areas with limited sand and steady wind direction.

Transverse dunes

Long ridges of sand oriented perpendicular to the wind, formed in areas with abundant sand and constant wind.

Barchanoid dunes

Wavy, connected dunes intermediate between barchan and transverse dunes.

Longitudinal dunes

Long, parallel ridges of sand formed by winds blowing from slightly different directions.

Parabolic dunes

U-shaped dunes with tips pointing upwind, often stabilized by vegetation.

Star dunes

Large, pyramid-shaped dunes with multiple arms, formed by variable wind directions.