glaciers Flashcards
what two epochs did the quarternary contain?
- pleistocene- ended about 10,000 years ago
- holocene, began about 10,000 years ago
when was ice at its maximum
-about 20,000 years ago during the pleistocene
what was the name of the less glacial?
-Loch Lomond stadial- ice reached scotland
give en example of a cold period during the holocene
-the little ice age between 13th and 18th centuries
how do milankovitch cycles effect climate change
-obliquity
the tilt angle of the earth, changes every 41,000 years- when tilt angle increases, summers hotter and winters cooler
-precession
earth slowly wobbles on its axis
-changes in solar output
amount of energy from sun varies due to hotspots where radiation is more active than usual. can dissappear for short periods- thought to have triggered the little ice age
apart from milankovitch cycles, what are other causes of climate change?
- the enhanced greenhouse effect- anthropogenic impactcs
- volcanic activity- ash and sulphur dioxide reflecting radiation e.g. 1815, Indonesia, largest wolcanic eruption in human history
what evidence is there of the pleistocene?
- UKs relict landscape, provides evidence that the country was once covered by ice
- depositional features
- erosional evidence
- meltwater evidence
what is permafrost?
- where a layer of sediment, soil or rock below the grounds surface remains almost permanently frozen
- reaches depths of up to 400-500m
- may be continuous, discontinuous or sporadic depending on the temp of the environment
what are the typical characteristics of permafrost areas
- cover about 25% of land area, but in the past their extent was greater
- typically large expanses of featurless land, with blockfields and with marshy, low growing vegetation
- plants include mosses- adapted to living in harsh environments
- thaw lakes are common in the summer. Water is darker, absorbs radiation, increases depth of thawing, creates talik
describe the process of frost heave, in periglacial areas
- upward dislocation of soil and rocks by the freezing and expansion of soil water
- frost push occurs when cold penetrates into the ground
- stones chilled more than surrounding soil, water below the stones freezes and pushes up the stones
- frost pull- alters orientation of stones, causing to stand upright
what is solidfluction
- mass movement of soil and regolith affected by alternate freezing and thawing- can be effected by nivation
- forms solidfluction lobes
give three periglacial landscapes
- pingos
- ice wedges
- patterned ground
what are pingos. describe formation of open system and closed system pingos
-domed shaped hills, 500m diameter, up to 50m in height
-at the core is an ice lens, surface layer usually vegetation. surface may contain cracks due to ground swelling
open system
-water forming the pingo comes from outside the system
closed system
-found at lakes and flat area- continuous permafrost
-e.g. in the mackenzie delta, canada
how are ice wedges formed
- frozen ice within crack in the ground
- ice melts
- more water enters the crack
- freezes, crack expands
- dust and sediment can collect in the crack to form ice wedge molds
how is patterened ground formed?
- as hydrostatic pressure rises, moisture in the ground begins to freeze and rise. forms and ice lens
- capillary action- leads to more moisture joining the ice lens, grows
- lens begins to push stones that are above it- stones have lower heat capacity, so ice lens forms around them7
- smaller sediment filters into the gap left when larger stones are pushed upwards
- stones now poke out of the ground
- ground polygons are formed, patterned ground formed
- stripes form when patterned occurs on slopes
give the characteristics of glacial advance
- equilibrium zone further down the glacier
- snout advance- further reach
- ice is thicker
- moves faster
- there is a positive mass balance
what factors control glacial movement
- gravity- steeper gradient=greater gravitational potential
- friction
- seasons ie. more melting in the summer- negative mass balance
- temerature of ice- temperate glaciers and higher altitudes, lower latitudes- lower temp
- geology- moves faster over impermeable rock
- mass of ice- thicker ice moves faster
what are the processes of glacial movement
- pressure melting point-glacial ice can melt at temps below 0 degrees
- basal slippage- increased friction and pressure at the base
- regulation creep- when glacier meets an obstacle, pressure increases. As stress increases, ice acts like a plastic flows over or around the glacier. less likely at polar glaciers as the lower the temp, the more pressure needed for this to occur
- extending and compressing flow- reduction in gradient, ice decelerates and becomes thicker- erosion greatest here
- surges- may be due to great snowfall in accumulation zone, glacier is out of equilibria
- internal deformation- movement between ice crystals, orientate themselves in direction of flow. cold based move predominantly by internal deformation
