Lecture 21 Flashcards
Glacier
Accumulation of ice affected by past or present movement.
Snow falling in winter exceeds snow melting in summer, so layer left at end of the year, then another year, etc.
Snow turns to ice. Thick ice flows under its own weight.
Continental glaciers
Cover large areas, like Antarctica and Greenland.
Alpine glaciers
Found in mountainous areas.
Quaternary
The last 2.6 million years, designated as the time of ice ages.
Broken up into two time periods.
Pleistocene
Majority of the Quaternary.
Holocene
Roughly the last 10,000 years (when humans developed agriculture, cities, and civilizations).
Glacier Mass Balance
Accounting system for gains and losses of ice.
Accumulation
Gain. Snow, rain, avalanches.
Zone of accumulation; part of glacier where accumulation exceeds ablation.
Ablation
Loss. Melting, sublimation, calving (results in icebergs).
Plucking
Ice melts at base, liquid water gets in cracks in bedrock and refreezes; rocks break free and carried away by ice.
Form of glacial erosion.
Scour
Rock particles at base wear way bedrock surface. Glacial erosion.
Fine material; glacial polish.
Big particles; striation.
Cirque
At upper part of alpine glacier, plucking erodes the headwall, forming amphitheater-shaped cirque.
Arête
Adjacent cirques may form a sharp ridge.
Horn
Three or four cirques may form a sharp peak.
Hanging valleys
After glaciers go away, tributary valleys may be at a different level.
Lateral moraine
Top of alpine glaciers gets sediment dumped on it. Here it is dumped on side.
Medial moraine
Here is dumped in the middle (from lateral moraine merging when tributary joins).
Terminal moriane
Most glacial sediment gets transported to front of glacier and dumped. Here deposit left at furtherest extent of glacier.
Recessional moraine
Deposit left as glacier is retreating, usually where it stops for a time or advances some.
Drumlins
Streamlined hills formed beneath glaciers, often found in groups.
Kettle
Block of ice buried by sediment, when ice melts, depression remains.
Erratics
Boulders deposited far from their bedrock source.
Eskers
Sinuous ridge of sediment deposited by stream under ice.
Isostatic rebound
During an ice age, weight of ice causes the crust to sink. When ice leaves, the crust rises.
Periglacial
Very cold, but not ice covered landscape.
Permafrost
Permanently frozen ground; most soil moisture does not melt.
Patterned ground
Polygons (lines of bigger rocks) develop on ground surface. Somehow related to freezing and thawing of active layer, large rocks moved around and accumulate in lines.
