Glaciation EQ1 Flashcards
What are the two dominant stages the Earth fluctuates between and what are their definitions ?
Greenhouse Earth: When there are no continental glaciers on the planet due to the warming processes of greenhouse gasses
Icehouse Earth: a global ice age when large ice sheets are present on Earth, this period fluctuates between glacial and interglacial periods
How is geological time divided ?
Era, Period, Epoch
What is the Pleistocene epoch known as and why?
Known as the ice age and is characterised by over 50 glacial-interglacial cycles where glaciers reached their maximum
What are the long term causes of climate change ?
Milankovitch cycles:
Shift in obliquity, 3 degree shift over 41,000 years
Eccentricity, Earths solar orbit varies in distance due to shift in elliptical orbit and circular orbit
Precession, Earths wobble on its axis due to the tidal forces of the sun and moon
What are the positive feedback mechanisms present in increasing the warming or cooling rates?
Decreased temperatures increase snow cover, snow cover increases albedo leading to further cooling
Melting snow/ice cover by GHG decreases albedo and methane is emitted as permafrost melts which leads to further Greenhouse effects
What are the negative feedback mechanisms present in increasing the warming or cooling rates?
When warming, evaporation increases, greater pollution from industrialisation leafs to increases cloud cover and increasingly cloudy skies and particulates causing global dimming which reduces solar radiation and warming
Ice sheet dynamics disrupt thermohailine circulation which disrupts ocean currents such as the gulf stream, less warm water is drawn north which leads to cooling in Northern Europe
What are the short term causes of climate change?
Solar output variation:
-Variations in solar activity causes variations in thermal energy transferred to Earth
-vary over 11 years, cooler temperatures occurred from 1300-1870, period known as little ice age
Volcanic emissions:
-Volcanic eruptions inject many particulates and sulphur dioxide into the atmosphere which causes a blanket effect on the atmosphere which blocks solar radiation, these can stay in the atmosphere for up to 3 years
Describe the characteristics of the Loch Lomond Stadial
Abrupt period of renewed cooling with regrowth of glaciers in upland Britain about 12,500 years ago
Temperatures were 6-7C lower leading to advance of many glaciers in Scotland and the formation of ice caps in Northern Scotland from which cirque valley glaciers moved outwards with smaller cirque glaciers in northern wales
Ice core data suggests 7C rise after the event
suggested that it was caused by drainage of huge proglacial lake Agassiz which disrupted THC and cut off pole ward transport to gulf stream
Describe the characteristic of the Little Ice age:
-Between 1550-1750
Effects:
-Abandonment of northern Scandinavia
-Re-advancement of European glaciers down valleys, predominantly positive mass balance leaving terminal moraines from which glaciers retreated
-Arctic sea ice spread further south (polar bears seen in Iceland), rivers in UK and Europe froze
-Holocene period
-different attributed causes (volcanic eruption, solar output)
-since lil ice age, glaciers in swiss alps retreated 2.3km
-Many crops failed
What are ice shelfs
Ice sheets which extend out to sea, unconstrained, e.g. princess Elizabeth in east antarctica
What are the 3 types of glaciers
Cold based, warm based, polythermal
What are warm based glaciers
A
Occur in high altitude areas outside polar regions e.g. alps
base is above the melting point, either from friction or geothermal heat so meltwater created acts as a lubricant causing it to move easily
ice at the top of the glacier melts during summer months which increases lubrication due to an increase in meltwater
high levels of erosion cause many debris to be entrained in the base
what are cold-based glaciers
high altitudes in polar regions e.g. Antarctica and Greenland
average temperature of ice is usually well below 0, due to extreme surface temperature (-20 to -30) and accumulation of geothermal sources is not enough to raise its temperature above 0c, despite ice sometimes being up to 500m thick
little surface melt in short polar summer
glacier is permanently frozen to its bed so no entrained debris
What are polythermal glaciers
Hybrid glacier where underneath is warm (wet) based and the margin is cold-based
many glaciers are cold-based in the upper region and warm in the lower region when they extend to lower climate zones, this is common in Svalbard, Norway
ice sheet
mass of ice or snow covering an area of 50,000 km^2, they bury entire landscapes including tall mountains, unconstrained, e.g. Antarctic ice sheet
Ice Cap
Dome-shaped Ice mass which covers less than 50,000km^2, usually on high ground, unconstrained, e.g. Vatnajokull, Iceland
Ice field
smaller than ice caps and defined by surrounding land, constrained
valley glacier
glacier bound by walls of a valley, descends from high mountains from an ice cap on a plateau or from an icesheet, constrained
Piedmont glacier
Glacier that spreads out wide in a love shape as it leaves a narrow valley to enter a wider valley or plain
cirque glacier
glacier occupying a cirque (corrie), Teton glacier in grand Tetons national park, Wyoming, USA
compare present-day distribution of high altitude ice sheets and Pleistocene ice extents
Ice covers at pleistocene macimum was 3x greater than modern day
antartica and Greenland ice sheets only slightly larger in pleistocene
major extensions were north american and scandiavian ice sheets which all grw to thickness of 3km-4km
other significant extensions were in new zealand, south america, sibera and himalayas
What evidence is there for the pleistocene period
depositional: drumlins (vale of eden, cumbria), erratics (bowder stone, lake district), moraine (ciargorns)
erosional evidence: aretes, glacial troughs along with roche mountanees, crag and tail, knock and lochan
meltwater evidence: meltwater channels (north yorkshire), glacial till (norfolk)
permafrost
Soil and rock that remains frozen as long as temperatures do not exceed 0C in summer months for at least 2 consecutive years
Characteristics of continuous permafrost
latitude: 75-65 N
temperature: -6 - 40c
depth of permafrost: 0.5 - 400m
depth of active layer: 0.5m
name the characteristics of discountinuous permafrost
latitude: 65 - 60 S
temperature: -1 - -6c
depth of permafrost: 1.5 - 40m
depth of active layer: 1 - 1.5m
What is the active layer
energy balance is positive in the summer, overlying snow and ice melts to produce a seasonally unfrozen zone above the permafrost called the active layer, which varies from a few centimetres to 3m (sporadic)
what factors affect the distribution and character of permafrost
Climate: main control as temperature and the amount of moisture available determine the persence or absence, depth and extent of permafrost
Proximity to water: areas near water have little to no permafrost called Taliks
Slope orientation: Less sunlight in south
Character of ground surface: some soils freeze more easily than others e.g. light coloured soils
Periglacial features
solifluction fields
blockfields
ice wedge polygons
nivation hollows
describe the process of solufluction
summer thaw of active layer creates meltwater
meltwater is unable to percolate down to rocks so it saturates the soil
internal friction coupled with lack of stability via vegitation causes the soil to flow on the slope
this flow causes the formation of solufluction lobes which are stepped features
most common where vegitation is spares with impermeable rocks
describe the process of ground contraction
(downward-tapeing bodies of ice)
when the active layer refreezes during the winter months, the soil begins to contract
as the meltwater contains fine sediments, it begins to fill the crack. The process contimues through the cycle of winter and summer months, widening and deepening the crack to form an ice wedge which over a period of hundreds of years can become 1m wide and 2-3m deep
-The craking produces a pattern on the surface which when viewed from above is similar to the polygons produced by frost heaving
-these are therefore known as ice-polygons when an ice wedge melts. it may fill with sediment to form an ice wedge cast
explain the process of nivation
beneath the patches of snow in hollows particularly at high altitudes on North and East facing slopes
when snow gets into a hollow in the ground, it can increase the size of the hollow. The temperature often fluctuates around 0C so lot of freeing and thawing happens when the temperature is above 0C, the snow melts and when it is below 0C, the water refreezes as ice
as ice refreezes it expands and contrats and so freeze thaw action and chemical weathering operating under the snow causes the underlying rock to disintergrate
As snow melts in the spring (increased solar isnsolation), the weathered rock debri are moved downslope by the meltwater and solufluction
over some period of time, the hollows envelope and become wider, the collective process is called nivation
hollows formed by nivation are known as nivation hollows
