GEOL 1500 Dynamic Earth Glacial Features

Vocabulary terms and definitions related to glacial geology, erosional and depositional landforms, and the causes of ice ages based on Chapter 18 lecture notes.

Louis Agassiz

A Swiss-American geologist who recognized in the 1830s and 1840s that glaciers explained erratic boulders and were powerful agents of landscape change.

Ice

Solid water ($H_2O$) that grows as hexagonal crystals when water cools below the freezing point; it is considered a mineral that forms rock types such as igneous, sedimentary, and metamorphic ice.

Firn

Compacted and melted snow that recrystallizes into glacial ice, with air content decreasing as it ages.

Cirque glaciers

Mountain glaciers that fill bowl-shaped basins at the uppermost portion of a glacial valley.

Valley glaciers

Rivers of ice that flow through existing valleys from higher to lower elevations.

Mountain ice caps

Glacial ice that covers mountain peaks and ridges.

Piedmont glaciers

Glaciers that spread out at the base or end of a mountain valley.

Continental glaciers

Vast ice sheets that cover large areas of continents, with major examples today being Antarctica and Greenland.

Crevasses

Cracks that form in the brittle upper layer of a glacier, occurring where ice bends while flowing over ridges; they do not typically extend below $ext{~60 m}$ depth.

Zone of accumulation

The area of a glacier where snow addition exceeds loss, causing ice to move downward.

Zone of ablation

The area of a glacier where ice loss (melting/sublimation) exceeds snow addition.

Equilibrium line

The boundary that separates the zone of accumulation from the zone of ablation.

Ice shelves

Broad, flat sheets of ice formed where continental glaciers flow out over ocean water.

Tidewater glaciers

Valley glaciers that terminate in the ocean.

Calving

The process where the leading edge of a glacier breaks away to form icebergs.

Sea ice

Nonglacial ice formed from frozen seawater, covering most of the Arctic Ocean and fringing Antarctica.

Rock flour

Fine pulverized rock produced when fragments embedded in glacial ice abrade and polish the underlying bedrock.

Striations

Grooves or gouges carved into bedrock by large rocks dragged across it by a glacier.

Roche moutonnée

An asymmetric bedrock hill shaped by glacial flow, featuring abrasion on the upstream side and plucking on the downstream side.

U-shaped trough valley

A distinctive steep-sided, flat-bottomed valley created by glacial erosion, differing from V-shaped fluvial valleys.

Hanging valley

A tributary valley left high above the main trunk valley floor after a larger glacier incises deeper than its smaller flows.

Arête

A knife-edge ridge formed by two cirques that have eroded toward one another.

Horn

A pointed mountain peak formed by the intersection of three or more cirques, such as the Matterhorn.

Fjords

U-shaped glacial valleys that have been flooded by rising sea levels.

Lateral moraines

Accumulations of sediment that form along either side of a valley glacier.

Medial moraines

Ridges of sediment occurring in the middle of a valley glacier, resulting from the merging of two lateral moraines.

Glacial till

Unsorted, unstratified sediment dropped directly by glacial ice, containing a range of grain sizes from boulders to clay.

Glacial erratics

Cobbles and boulders dropped by a glacier that differ from the underlying bedrock.

Outwash

Stratified and sorted sand and gravel transported by glacial meltwater, with muds removed.

Loess

Wind-transported silt derived from fine sediment produced by glaciers.

Varve

Seasonal layers in glacial lake sediments, reflecting winter silt/clay and summer coarser sand/silt.

Drumlins

Elongate, tapered hills of molded glacial till that are steep on the up-ice side and tapered on the down-ice side.

Eskers

Long, sinuous ridges of sand and gravel formed by meltwater channels within or below glacial ice.

Post-glacial rebound

The rising of the land after the weight of a melted ice sheet is removed, following previous lithospheric depression.

Milanković Cycles

The collective name for cyclic changes in Earth's orbital geometry (precession, obliquity, and eccentricity) hypothesized to predict climate variation over $100$ to $300$ Ka.

Precession

The 'wobble' of Earth's axis occurring with a $23,000$-year periodicity.

Obliquity

The change in the angle of Earth's rotational axis, occurring with a $41,000$-year periodicity.

Eccentricity

The variation in the shape of Earth's orbit around the Sun, occurring with a $100,000$-year periodicity.