Glaciers cover 10% of the Earth's land surface.
Glacier: thick mass of ice that forms over hundreds or thousands of years, originates on land from the accumulation, compaction and recrystallization of snow.
There are two types of glaciers:
continental ice sheets: There are two that exist today: Greenland (1500 meters thick) and Antarctic (4300 meters thick)
alpine glaciers: exist in mountain valleys originally occupied by streams.
Flow: plastic movement within the ice that causes slippage along the ground
Zone of fracture: uppermost 50 meters of a glacier - brittle ice is carried on top of "plastic" ice
Crevasses:cracks in the zone of fracture.
Zone of accumulation:net gain of snow
Zone of wastage:net loss of snow
Calving:large pieces of glaciers break off to form icebergs. Icebergs are 80% submerged.
Plucking: glaciers loosen and lift rock, incorporate it and carry it.
Abrasion: produces pulverized rock flour.
Glacial striations: scratches and grooves as the glacier scrapes the ground
Glacial trough: U-shaped
Hanging Valleys: tributary valley that enters glacial trough above its floor
There are glacial/interglacial cycles every 100,000 years
Great Ice Ages occurred 2 billion, 600 million, 250 million and 2 million years ago
Pleistocene: The ice age that occurred 2 million years ago
One result from the pleistocene was a pluvial lake e.g. Great Salt Lake
A desert is arid and a steppe is semiarid.
Deserts that are located in the lower latitudes are formed because of subtropical high pressure zones. Sinking air is compressed and warmed.
Desert streams are ephemeral i.e. they come and go quickly and they don't last. Ephemeral streams have many names e.g. wash, arroyo
Desert floods occur because the rain cannot soak into the ground. They arrive quickly and subside quickly.
Desert streams lack extensive tributaries.
Desert streams lack extensive tributaries.
Running water is responsible for most of the erosional work in deserts even though it is infrequent.
Over time the relief in a desert diminishes.
Bajada: a series of alluvial fans
Playa lake: shallow, short-lived lake
Borax (sodium borate) is mined from ancient playa lake deposits in Death Valley (View photos of Death Valley)
Inselberg: top of a "mountain" buried in desert sand. (view images)
In humid regions wind erosion is negligible but in the desert wind erosion is significant. Why?
Wind has a low density and cannot pick up large particles.
Wind is not confined to channels
Deflation the lifting and removal of loose material by wind
Blowouts shallow depressions created by deflation
Desert pavement coarse pebbles too large to be moved by the wind, left behind (view images one two three)
Once desert pavement is established the surface is protected from further deflation unless the pavement is dislodged.
There are two distinct types of wind deposits:
Loess deposits of windblown silt
Sand dunes mounds or ridges of sand
slip face leeward (side opposite where the wind hits directly) slope of the dune