Systems and Processes in Glaciers and Glacial Landscapes Flashcards
What are the inputs in a glacial system?
Direct snowfall
Blown snow
Avalanches/rock falls
What is the snow line?
During the summer the glacier retreats, during the winter the glacier advance. Shorter summers allow less time for snow to melt. This leads to permanent snow cover in upland areas, the lower edge of which, is the snow line. As mean annual temperatures drop, the snow line moves down the slope.
What is the zone of accumulation?
The upper part of the glacier where inputs exceed outputs and mass is gained.
What is the zone of ablation?
The lower part of the glacier where outputs exceed inputs and mass is gained.
What is the equilibrium line?
The boundary between ablation and accumulation where net gain and loss are balanced.
What are the characteristics of temperate/warm based glaciers?
More mobile - more meltwater, meaning more likely to erode, transport and deposit
The surface is thin and subject to seasonal temperature fluctuations - melts rapidly at around 0 degrees Celsius
Pressure melting point occurs - where the glacier is near melting point because of warmer atmospheric temperatures and the weight of the ice above.
What are the characteristics of polar/cold based glaciers?
Very old
Very little meltwater - geothermal and atmospheric heat isn’t enough to reach melting point
Moves very slowly - often frozen to their beds, most movement is from internal flow
Less erosion, transportation and deposition.
What is weathering?
The breakdown/decay of rock though mechanical, biological or chemical processes.
What are frost-action/threeze-thaw cycles?
Water enters cracks during day, then at night the water freezes in the cracks. This expands and makes the cracks bigger through repeating the cycle.
What is nivation?
Processes that happen under patches of snow in hollows. Freeze-thaw and chemical weathering causes underlying rock to disintegrate. When the snow melts in the spring the ,material is flushed-out and moved downslope through solifluction and meltwater. Repeated seasons of this causes nivation hollows - the start of a corrie.
What is internal deformation?
When ice is frozen to the bed and added pressure builds up within the glacier. This allows the ice to behave with plasticity and flow, and ice crystals inside move past each other.
What is rotational flow?
When a glacier in a corrie pivots and rotates, this with increased pressure leads to greater erosion and over deepening of the corrie floor.
What is compressional flow?
Occurs when there is a reduction in the gradient of the valley floor, leading to deceleration and more accumulation of mass. This increases ice erosion.
What is extensional flow?
Occurs when there is an increase in the gradient of the valley floor, leading to acceleration and an ablation of ice. This decreases ice erosion.
What is basal sliding?
When a glacier moves over bedrock friction and pressure allows more melting - meltwater acts as a lubricant and ice flows more rapidly.
What are surges?
When glaciers move forward very suddenly due to an excessive build up of meltwater - can move as much as 250-300 m in one day
What is abrasion?
Happens when the material the glacier is carrying rubs at the valley floor/sides.
Coarser, harder debris leaves striations.
Finer debris polishes and smooths rock.
The debris involved is usually worn down into rock flour.
What is sub-glacial debris?
Material found at the base of a glacier
What is en-glacial debris?
Buried within the ice
What is supra-glacial debris?
Carried on top of the glacier
What is till?
Material deposited directly by ice.
An unsorted mixture of rocks, clay and sand that was mainly transported supra-glacial and en-glacial.
Till reflects the character of the rocks over which the glacier has passed.
What are corries?
Armchair shaped rock hollows with steep back walls and over deepened basins, with a rock lip.
Often contains a small lake - a tarn
Found on north, north-east, and east facing slopes where lower levels of insulation allowed increased accumulation of snow.
Dimensions of the corries depends on the topography of the area and the size of the glacier that formed them.
What is an arete?
When two corries are back to back or alongside each other, if enlarged over many glaciations, a narrow steep-sided ridge between the two hollows is formed.
What is a pyramidal peak?
When more than two corries develop on a mountain the remaining central mass will survive as a pyramidal peak
Which appears sharp because of frost shattering
e.g. The Matterhorn in the Alps bordering Switzerland
What are glacial troughs?
Glaciers straighten, widen and deepen V shaped valleys into a U shaped valley.
Ice + Meltwater + Sub-glacial debris = glacial trough
Contains rock basins filled with ribbon lakes
Contains fjords
Contains hanging valleys
Contains truncated spurs
Contains roches moutonnees
What are fjords?
Over deepening past the present sea level leads to the formation of fjords when sea levels rose after ice ages
What are hanging valleys?
On the side of the main valley
Either pre-glacial tributary river valleys that were not glaciatied
Or smaller tributary glacial valleys - with small glaciers, resulting in less erosion than the main valley
Higher than the main valley when the ice retreated
What are truncated spurs?
Areas of land projecting from the river-valley side that have been removed by the glacier
What are rouches moutonnees?
Small mounds of resistant rock on the valley floor that aren’t completely removed by the glacier.
Have an up/stoss slope (which is smooth from abrasion) and a down/lee slope (which is jagged from plucking)
What is lodgement till?
Sub-glacial material that was deposited by an actively moving glacier - e.g. a Drumlin
What is ablation till?
Produced at the snout when the ice melts - e.g Terminal, push and recessional moraine
What are drumlins?
Smooth egg shaped small hills
Have a steeper upstream end and gently sloping downstream end
Elongated in the direction of ice advance
Formed from unsorted till with little internal structure
How are drumlins formed?
Ice becomes overloaded with debris and capacity to carry is reached. Deposition occurs at the base of the ice and this material is shaped by further glacier advance.
What are terminal moraines?
Formed at the snout when the glacier has reached its furthest extent downstream
What are recessional moraines?
As the glacier retreats, moraine form along the length of the valley showing points where retreat paused
What are push moraines?
When a glacier advances previously deposited moraine is moved forward into a mound
What are till plains?
Wide areas of flat relief created by a till sheet.
Hidden by a thick covering of glacial till, sands and gravel.
Material is compacted giving poor drainage - bogs lakes and slow moving meandering streams
Explain the theoretical stages in the diversion of the river Severn.
Pre-Glacial - flowed northwards into the irish sea
The last ice age - Ice blocked the river Severn from the north and the water from the blocked river formed a huge pro-glacial lake - Lake Lapworth. The lake eventually overflowed the watershed to join the original Lower Severn, cutting through a solid rock area and creating a gorge at Ironbridge
Deglaciation - As ice retreated to the north the route north was still blocked with deposits and the Ironbridge gorge was cut deep so the river severn now flows from wales to the Bristol Channel
Explain pro-glacial lakes and overflow channels
When rivers get blocked during glaciation and form lakes.
Then when lake overflows it creates overflow channels
What are eskers?
Long ridges of material running in the direction of ice advance - often stratisfied/layered
Made by sub-glacial streams
What are kames?
Mounds of fluvio-glacial material left when meltwater flows into a lake and dams the front of the glacial snout by recessional moraine deposits. When ice retreats further the delta kame collapses.
What are outwash planes?
In front of a glacier snout, deposited by meltwater streams.
Material brought by the glacier, picked up, sorted and then dropped.
Coarsest material travels shortest distance and fine material is deposited far
Layered vertically to show the seasonal flow of meltwater streams
