glaciation Flashcards
(39 cards)
glacials and interglacials?
glacials are warm phases and interglacials are warm phases
what theories are there for the cause of ice ages
- variations in sunspot activity may increase or decrease amount of radiation received
- volcanic dust ejected into the atmosphere reflect and absorb radiation from the sun
- increased co2 by greenhouse gases can be absorbed by the sea in time leading to an overall drop in world land temperatures
- changes in ocean currents or jet streams
- earths position in space, its tilt and its orbit effect incoming radiation
what is the snow line?
level above which snow will lie all year
why is the snow line in northern hemisphere at lower altitudes on north facing slopes?
these receive less insolation than south facing slopes
what is a firn?
compacted snow which has experienced one winters freezing and survived a summers melting. it is composed of randomly orientated ice crystals separated by air passages
how are glaciers formed?
summer meltwater percolates into the firn only to freeze either at night or during the following winter… forming an incredibly dense mass
cirque glaciers
small masses of ice occupying armchair shaped hollows in mountains, often overspilling to feed valley glaciers
valley glaciers
large masses of ice which move down from either an ice field or a cirque basin source. they usually follow former river courses and are bounded by steep sides
piedmont glaciers
formed when valley glaciers extend onto lowland areas, spread out and move
ice caps or ice sheets?
huge areas of ice which spread outwards from central domes.
nunataks
exposed summits of high mountains
ice shelves
form when ice sheets reach the sea and begin to flirt
upper part of of the glacier where inputs exceed outputs
zone of accumalation
zone of ablation
lower part where outputs exceed inputs
zone of equilibrium
where the rates of accumulation and ablation are equal, and it corresponds with the snow line
polar glaciers
occur in areas where no melting occurs and where relief is usually gentle. base is much colder than pressure melting point so no melting occurs
temperate glaciers
occur in areas with milder summers allowing melting to occur and where relief is steeper. the base of a temperate glacier is about the same temperature as the pressure melting point
internal flow
in very cold climates glacier will be frozen to its bed. without any friction or pressure increase there will be no more melting. such glaciers move only 1 - 2cm per day with minimal erosion
basal slippage
if glacier moves, pressure and friction increases with the bedrock. this raises temperature and basal ice may melt, resulting meltwater will act as lubricant enabling glacier to move more rapidly at 2-3m per day
creep?
obstacle in path of glacier increases pressure and stress. as this builds up, ice behaves like plastic and flows around or over the obstacle
extending and compressing flow?
compressing flow - where there was a reduction in gradient of the valley floor, ice would slow down and become thicker
extending flow - valley gradient steepened and ice accelerates and becomes thinner
surges
result of an excessive build up of meltwater, can move glacier by 300m in one day
pressure melting point
temperature at which ice is on the verge of melting
by which 4 processes does movement in a glacier take place
basal flow, creep, extending - compressing flow and surges
