glaciation Flashcards
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
in what 3 ways do glaciers move debris
supraglacial debris, englacial debris, subglacial debris
supraglacial debris
carried on the surface as lateral and medial moraine. consists of material that has fallen onto glacier from valley sides
englacial debris
material carried within the body of the glacier
subglacial debris
moved along the floor of the valley either by the ice or meltwater streams formed by pressure melting
what are the processes associated with glacial erosion
frost shattering, abrasion, plucking, rotational movement, and extending and compressing flow
what is frost shattering
produces loose material that will fall from the valley sides to form lateral moraine
then either covered all falls down crevices to be transported as englacial debris
abrasion?
sandpaper effect of material rubbing against valley sides while be transported, creating smooth gentle landforms
plucking
process involves the glacier freezing onto rock outcrops, after which ice movement pulls away masses of rock
a bergschrund?
large crevasse like feature found near the head of some glaciers
rotational movement?
downhill movement of ice, pivots about a point. increase in pressure is responsible for the over deepening of the cirque floor
Aretes and Pyramidical peaks?
Arete - when two adjacent erode backwards or sideways toward each other, the previously rounded landscape is transformed into a narrow, rocky, steep sided ridge
Pyramidical Peak - if three or more cirques develop develop on a mountain, having several aretes and steep sides radiating from a central peak
glacial troughs
steep sided flat floored valleys
ribbon lakes and rock steps?
overdeepening of the trough floor, creating river like features, or may leave less eroded, more resistant rock steps.
truncated spurs?
cliff like features formed by abrasion by englacial and subglacial and plucking along the valley sides to remove the tips of preglacial interlocking spurs
hanging valleys
results from differential erosion between main glacier and its tributary. floor of tributary deepened at a slower rate than the main channel, as ice melts, tributaries are left high above the main vallley
