Glaciation Flashcards
(40 cards)
What is a glacier
Slowly moving mass or river of ice formed by the accumulation of snow on mountains or near the poles
Ice cap
Mass that covers less than 50,000 km of land area
Ice sheet
Mass of glacier that covers surrounding terrain and is greater than 50,000 km2
Quaternary period
Last c.2 million years
Pleistocene epoch
From 11,700-1.8 million years bp
Holocene epoch
Last 11,700 years
Describe the Pleistocene
- at the time the continents had moved to their current positions
- sheets of ice covered all of Antarctica, large parts of Europe, North America , South America and small areas inn Asia
-consisted of about 20 cycles of glaciers retreating and thawing
Evidence for climate change
-ice cores:ice cores contain information about past temperatures and many other aspects of the environment. They enclose small bubbles of air that contains sample of the atmosphere(co2 levels indicate global temperatures at the time
-oxygen isotopes: they indicate past climatic conditions. The technique involves the ratio between heavy and light oxygen in marine sediments
Eccentricity
Earths orbit moving from circular to more elliptical, changing the amount of radiation the Earth receives. Occurs every 100,000 years
Obliquity
Tilt of the earths axis which affects the earths seasonal extent . Occurs every 41,000 years
Precession
The direction of the earths axis rotation it affects the timings of the seasons . It occurs every 21,000 years
Other causes of climate change
- volcanic activity as it lowers global temperatures
-variations in sunspot activity as sunspot activity significantly affects our climate
Periglacial environment
Cold climate typically near glacial regions,often marginal to a glacial environment and is subject to intense cycles of freezing and thawing
List the types of permafrost
Continuous
Discontinuous
Sporadic
Permafrost
Where the ground is frozen for more than 2 years in a row
Continuous permafrost
Sheet of frozen material
Discontinues permafrost
Where the permafrost melts partially, usually the lower layer remains frozen
Sporadic permafrost
Occurs at margins of periglacial environments and is usually very fragmented and only a few meters thick
Characteristics of periglacial environments
-found close to glacial environments
-characterised by permafrost and cycles of intense freezing and thawing
- talik( upper part ) may thaw
Periglacial environments
- frost heave: the concentration and cracking of rapidly freezing soils in which ice wedges and patterned ground are formed
-suction: the migration of sub surface water to the freezing front which causes the formation of ice lens and pingos
-solifluction: the mass movement of the saturated active layer downslope, largely by gravity,which leads to lobes and terraces - frost shattering(freeze thaw ): it is the 9% water expansion of water upon freezing which forms block fields and screes
-wind erosion: high winds disturb sediment which can build up in certain areas to create loess deposits
Formation of glaciers
- Snow accumulates and compacts into an upland nivation hollow.
- Over 3-4yrs, water is squeezed out of the ice, percolates down and refreezes onto the bottom of
the glacier (firn/nevé). - Gravity and the weight of the ice above will gradually further compact the ice until it becomes
glacier ice. - The glacier will then begin to flow over the lip as a result of gravity and the gradient of the
underlying slope.
Glacier mass balance
The net difference between accumulation and ablation over the course of one year
Basal slippage
Lower ice melts allowing glacier to move as one body (temperate glaciers)
Deformation
Individual ice crystals moving within the glacier. Ice at the surface and in the middle of glacier move faster due to less friction (temperate and polar glaciers).
