glaciated landscape Flashcards
whats glacier mass balance
the difference between the amount of snow and ice accumulation and the amount of ablation occurring in a glacier over a one year period
cold based glaciers
- low altitude
- low relief
- basal temperatures below the pressure point
- very slow rates of movement, perhaps a few meters/cm a year
warm based glaciers
- high altitude locations
- steep reliefs
- basal temperatures alter above the pressie melting point
- rapid rates of movement, typically 20-200 m/year
what are the open systems
means energy and matter can be transferred from neighbouring systems as an input. it can also be transferred to neighbouring systems as an output
whats a input
energy eg kinetic energy from wind
material from deposition weathering and mass movement from slopes
whats an output
glacial and wind erosion
evaporation
whats equilibrium
when a systems outputs and inputs are equal
whats dynamic equilibrium
when the equilibrium is disturbed, the system produces its own response to the disturbance. this response is an example of negative feedback
whats ablation
refers to all processes that remove mass from a glacier
what are the two key aspects that influence glaciated landscape systems
lithology and structure
whats lithology
describes the physical and chemical composition of rocks. for example some rocks such as clay have a weak lithology, with little resistance to erosion.
whats structure
concerns the properties of individual rock types such as jointing, bedding and faulting. it also includes the permeability of rocks.
high altitude
- beyond the artic and antarctic circles
- 66.5 degrees north and south
- tend to have cold dry climates with little seasonal variation in precipitation
low altitude
- high precipitation inputs
- variable temperatures
- more summer melting
what is relief
the term used for the differences in height from place to place on the land’s surface
effects of relief
the steeper the relief of the landscape the greater the resultant force of gravity and the more energy a glacier will have to move downslope.
whats aspect
the direction that a slope faces
effect of aspect
if the aspect of the slope faces away form the general direction of the sun, temperatures are likely to remain below zero for longer as less solar energy is received and so less melting occurs.
how does glacial ice form
glaciers form when temperatures are low enough for snow that falls in one year to remain frozen throughout the year. this means the following year fresh snow falls on top of the previous years snow.
each new fall of snow compresses and compacts the layer beneath, causing the air to be expelled and converting low density snow into higher density ice
what are valley glaciers
Valley and piedmont glaciers originate in the high alpine and terminate on land. They often flow through deep bedrock valleys that confine the ice on either side. Over time, they carve and shape these valleys (see U-Shaped Glacial Valleys)
why do glaciers move
- due to gravity
- the gradient, the steeper the gradient of the ground surface the faster the ice will move if other factors are excluded
- the thickness of the ice, as this influences basal temperature and the PMS
factors that influence the movement of glaciers
- gravity, the fundamental cause of the movement of an ice mass
- gradient, the steeper the gradient of the ground surface, the faster the ice will move if others factors are excluded
- the thickness of the ice, as this influences basal temp and the pressure melting point
- the internal temperatures of the ice, as this can allow movements of one area of ice relative to another
- the glacial budget, a positive budget (net accumulation) causes the glacier to advance
whats glacier mass balance
the difference between the amount of snow and ice accumulation and the amount of ablation occurring in a glacier over a one year period
what are niche glaciers
are small patches of ice found on upland slopes. they are most prevalent on north facing slopes in the northern hemisphere, they have relatively little effect on topography
what are cirque (corrie) glaciers
are small ice masses on mountain slopes which gradually erode armchair shaped hollows. if they develop to be too large for the hollow, they spill over the lip to feed into a valley glacier.
what are valley glaciers
large masses of ice that flow from ice fields or a cirque and usually follow periglacial river valleys, developing steep sides as they erode on course. this erosion is known as a U shaped valley
what are Piedmont glaciers
large lobes of ice when glaciers spread out. they may merge on reaching lowland areas and escape the confines of their U shaped valley
what are ice caps
they are huge flattened, dome shaped masses of ice that develop on high plateaus. they are similar to an ice sheet, but are less than 50,000km2 in area. (above 50,000km2 are ice sheets)
what are ice shelves
extensions of ice sheets that reach out over the sea. these shelves of floating ice can be up to 1km thick but diminish to around 500meters at the edge where the ice breaks off. this process if known as ‘calving’
why do glaciers form
snow compacts as new snow falls on top and turns to glacial ice
when does compression flow occur
occurs where there is a reduction in the gradient of the valley floor leading to ice deceleration and a thickening of the ice mass. at such points ice erosion is at its maximum
when does a creep occur
occurs when stress builds up within a glacier, allowing the ice to behave with plasticity and flow. it occurs partially when obstacles are met
when do surges occur
occurs from time to time when an excessive build up of meltwater under the glacier leads to the ice moving rapidly forward, perhaps by as much as 250-300 meters in one day.
what is basil flow
as the glacier moves over the bedrock there is friction. the lower ice is also under a great deal of pressure and this, combined with the friction, results in some melting. the resulting meltwater acts as a lubricant, enabling the ice to flow more rapidly
when does rotational slip occur
occurs within a corrie (cirque or cwm), the birthplace of many glaciers. here ice moving downhill can pivot about a point, producing a rotational movement. this combined with increased pressure with the rock hollow, leads to greater erosion and an over deepening of the corrie floor.
when does extended flow occur
occurs when the valley gradient becomes steeper. the ice accelerates and becomes thinner leading to reduced erosion
when does internal flow occur
occur when ice crystals orientate themselves in the directions of the glaciers movement and slide past each other. as surface ice moves faster, crevasses develop.
whats the geomorphic process of freeze thaw
water enters crack and expands by nearly 9 percent when it freezes. in confined spaces this exerts pressure as the rock causing it to split into pieces or break off. PHYSICAL/MECHANICAL
whats the geomorphic process of frost shattering
at extremely low temps, water trapped in rock pores freezes and expands. this creates stress which disintegrates rock to small particles. PHYSICAL/MECHANICAL
whats the geomorphic process of pressure release
when the weight of overlaying ice in a glacier is lost due to melting, the underlaying rock expands and fractures parallel to the surface. this is significant in the exposure of sub surface rocks such as granite and is also known as dilation. PHYSICAL/MECHANICAL
whats the geomorphic process of oxidation
sine minerals in rocks react with oxygen in air or water. iron is especially susceptible to this process. CHEMICAL
whats the geomorphic process of carbonation
rain water combines with dissolved carbon dioxide from the atmosphere to produce a weak carbonic acid. CHEMICAL
whats the geomorphic process of solution
some salts are soluble in water, any process by which a mineral dissolves in water is known as solution (PH around 3) CHEMICAL
what is the geomorphic process of tree roots
tree roots grow into cracks or joints in rocks and exert outward pressure. BIOLOGICAL
what is the geomorphic process of organic acids
produced during decomposition of plant and animal litter cause soil water to become more acidic and react with some minerals called chelation
whats endogenic
beneath earth surface
whats exogenic
on earth surface
what are the two key types of mass movement
rock fall and slides
whats rock fall
on slopes of 40 degrees or more, especially if the surface is bare, rocks nay become detached from the slope by physical weathering processes. these then fall to the foot of the slope under gravity. Transport processes may then remove this material, or it may accumulate as a relatively straight, lower angled scree slope.
what are slides
occurs when a portion of the soil or rock along a steep slope suddenly gives away and moves downhill, usually aided by heavy rainfall. Sliding mass movement occurs on slopes weakened by weathering such as landslides, rockslides, and mudslides.
what are the 4 types of mass movement
fall, slide, flow and creep
what are glacial processes
moving ice in a glacier is a source of energy in glaciated landscape systems, and the energy can be expended through geomorphic processes to shape landforms. These processes can also supply material in the form of sediment, which can be deposited in, or transported within the glacial system
what are plucking and abrasion
glacial erosion
what is plucking
As ice and glaciers move, they scrape along the surrounding rock and pull away pieces of rock which causes erosion.
whats abrasion
As a glacier flows downslope, it drags the rock, sediment, and debris in its basal ice over the bedrock beneath it, grinding it
what are the 8 factors that influence the rates of glacial abrasion
- basal debris
- debris size and shape
- bedrock/particles hardness
- thickness of ice
- basal water pressure
- removal of fine debris
- debris to base movement
- basal ice sliding
how does basal debris influence the rate of glacial abrasion
pure ice is unable to carry out abrasion of solid rock and so basal debris is an essential requirement.
how does debris size and shape influence the rate of glacial abrasion
particles embedded in ice exerts downward pressure proportional to their weight, and so larger debris is more effective in abrasion than fine material.
how does hardness of particles/bedrock influence the rate of glacial abrasion
abrasion is most effective when hard, resistant rock and debris at the glacier base is moved across a weak, soft bedrock. if the bedrock is more resistant than the debris then little abrasion will be accomplished
how does ice thickness influence the rate of glacial abrasion
the greater the thickness of overlying ice, the greater the pressure exerted On the basal debris and the greater the rate of abrasion. This is, however, only true up to a point.
Bevondha cars air thickness the pressure becomes too great and there is too much friction between the debris and the bedrock for much movement to occur. This is not a fixed thickness, as it depends upon ice density and the nature of the debris, but it is typically 100-200 m.
how does basal water pressure influence the rate of glacial abrasion
the presence of a layer of meltwater at the base of a glacier is vital if sliding and therefore abrasion is to take place. However, if the water is under pressure, perhaps because it is confined, the glacier can be buoyed up, reducing pressure and erosion.
how does sliding basal ice influence the rate of glacial abrasion
this is important as it determines whether abrasion can take place.
Abrasion requires basal sliding to move the embedded debris across the rock surfaces. The greater the rate of sliding, the more potential there is to erode as more debris is passing across the rock per unit of time.
how does movement of debris to the base influence the rate of glacial abrasion
abrasion does not only wear away the bedrock, it also wears away the basal debris. Debris needs to be replenished by glacial erosion and weathering processes) if abrasion is to remain effective.
how does removal of fine debris influence the rate of glacial abrasion
to maintain high rates of abrasion, rock flour (fine debris) needs to be removed so that the larger particles can abrade the bedrock.
This is mainlv done by meltwater.
whats nivation
Nivation is a glacial process that is not easily classifier as erosion or weathering. This complex process is thought to include a combination of freeze-thaw action, solifluction, transport by running water and. possibly, chemical weathering. Nivation is thought to be responsible for the initial enlargement of hillside hollows and the incipient development of corries.
what are the different types of glacial transportation
- rockfall
- avalanches
- debris flow
- aeolian deposits
- volcanic eruptions
- plucking
abrasion
what is rockfall in terms of glacial transportation
weathered debris falls under gravity from the exposed rock above the ice down onto the edge of the glacier
what are avalanches in terms of glacial transportation
these often contain rock debris within the snow and ice that moves under gravity
what is debris flow in terms of glacial transportation
in areas of high precipitation and occasional warmer periods, melting snow or ice can combine with scree, soil and mud
what is aeolian deposits in terms of glacial transportation
fine material carried and deposited by wind, often blowing across outwash deposits
what are volcanic eruptions in terms of glacial transportation
a source of ash and dust
what is plucking in terms of glacial transportation
large rocks plucked from the side and base of the valley
what is abrasion in terms of glacial transportation
small material worn away from the valley floors
what are the two types of glacial till
lodgement till
ablation till
whats lodgement till
this is material deposited by advancing ice. Due to the downward pressure exerted by thick ice, subglacial debris may be pressed and pushed into existing valley floor material and left behind as the ice moves forward. This may be enhanced by localised pressure melting around individual particles that are under significant weight and pressure. Drumlins are the main example of landforms of this type.
whats ablation till
this is material deposited by melting ice from glaciers that are stagnant or in retreat, either temporarily during a warm period or at the end of the glacial event. Most glacial depositional landforms are of this type.
both of these types of till have 3 distinct characteristics. what are they?
- angular or sub angular in shape
- unsorted
- unstratified
what are the different landforms caused by erosion
- corries
- aretes and pyramidal peaks
- troughs
- roche moutonnes and striations
- ellipsoidal basins
how are corries formed
- Snow collects in a sheltered hollow on the side of a mountain. This is usually on North-facing slopes in the northern hemisphere. The snow doesn’t melt in the summer because it is high up, sheltered and cold.
- Every winter, more snow collects in the hollow. This becomes compacted and the air is squeezed out leaving ice.
- The back wall of the corrie gets steeper due to freeze-thaw weathering and plucking
4.The base of the corrie becomes deeper due to abrasion
5.As the glacier gets heavier it moves downhill. The glacier moves out of the hollow in a circular motion called
rotational slip
6.Due to less erosion at the front of the glacier a corrie lip is formed.
7.After the glacier has melted a lake forms in the hollow. This is called a corrie lake or tarn.
what is a corrie
- arm chair shaped hollow found in upland hills or mountain sides. They have a steep back wall an over deepened basin and often have a lip at the front which may be solid rock or made of morinic deposits
whats an arête
is a narrow, steep sided rifle found between two corries. this ridge is often so narrow that it is described as knife edged
how’s an arête formed
It is formed when two corries run back to back. As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower.
hows a pyramidal peak formed
A pyramidal peak is formed where three or more corries and arêtes meet.
whats a trough (U shaped valley)
long U shaped valleys that were carved out by glaciers that have since receded or disappeared. Troughs tend to have flat Valley floors and steep straight sides
how is a trough formed
glaciers flow down pre existing river valleys under gravity. As they move the erode the sides and floor of the valley, causing the shape to become deeper, wider and straighter.
what are Roche moutnonees
a mass of resistant rock which has a smooth, rounded up valley (STOSS) slope facing direction of ice flow and down (LEE) slope by plucking. as the glacier encounters the obstacle pressure increases and allows melting to occur. this allows the ice to melt and basal sliding to occur, can leave strations.on the LEE side pressure falls and the water refreezes and as the ice moves downhill it pulls away masses of rock; plucking the rocks underneath, this leaves a steeper sided note jagged see slope.
what are striations
when ice passes over over the valley the valley is smooth and streamlined by abrasion and often has striations which are scratches or groves made by debris embedded in the base of a glacier
what are ellipsoidal basins
deep, elongated lakes, formed by subglacial activity beneath past ice sheets
major erosional landforms created by ice sheets. the Laurentide ice sheet covered much of North America between 95,000 and 12,000 years ago. erosion by the Laurentide ice sheet produed a series of ellipsoidal basins in North America.
whats glacial isostatic adjustment
the ongoing movement of land once burdened by ice-age glaciers. The last ice age occurred just 16,000 years ago, when great sheets of ice covered much of Earth’s Northern Hemisphere.
whats a moraine
- Moraines are distinct ridges or mounds of debris that are laid down directly by a glacier or pushed up by it.
- The term moraine is used to describe a wide variety of landforms created by the dumping, pushing, and squeezing of loose rock material, as well as the melting of glacial ice.
whats a terminal moraine
- is a moraine ridge that marks the maximum limit of a glacier advance.
- They form at the glacier terminus and mirror the shape of the ice margin at the time of deposition.
- The largest terminal moraines are formed by major continental ice sheets and can be over 100 m in height and 10s of kilometres long
whats a lateral moraine
- Form along the glacier side and consist of debris that falls or slumps from the valley wall or flows directly from the glacier surface.
- Where the rate of debris supply is high, lateral moraines can reach heights of more than 100 metres
whats recessional moraine
- are found behind a terminal moraine limit and form during short-lived phases of glacier advance or still stand that interrupt a general pattern of glacier retreat.
- In some cases, recessional moraines form on a yearly basis (normally as a result of winter glacier advances) and are known as annual moraines
what are push moraines
- when an advancing glacier pushes a pile of previously deposited glacial material into a linear ridge.
- These are found in areas where fluctuating climate has resulted in glacial advance followed by retreat and then advance again.
what are erratics
- rocks that have been transported by ice and deposited elsewhere. The type of rock (lithology) that the glacial erratic is made from is different to the lithology of the bedrock where the erratic is deposited.
what are drumlins
oval or elongated hill believed to have been formed by the streamlined movement of glacial ice sheets across rock debris, or till.
drumlins functions
there functions aren’t funny understood but they are guessed:
- lodgement of subglacial debris as it melts out of the basal ice layers
- reshaping of previously deposited material during a subsequence of re-advance
- accumulation of material around a bedrock obstruction these are known as rock cored drumlins
- thinning of ice as it spread out over a lowland area reducing its ability yo carry debris
whats a till sheet
a uniform blanket of glacial deposits in a lowland
how’s a till sheet formed
when a large mass off unstratified drift is deposited at the end off a period of ice sheet advance which smoothes the underlying surface
whats an ice sheet
a layer of ice covering an extensive tract of land for a long period of time.
whats a fluvio glacial landform
a landform which has been created by the meltwater from glaciers
whats outwash
the distinctive sediment only deposited by glacial meltwater
importance of glacial meltwater
- high up in the mountains, melting snow helps to enlarge the shallow nivation hollows that eventually become corries
- helps to lubricate the base of a glacier and overcome friction.
whats a kame
a hill or hummock composed of stratified sand and gravel laid down by glacial meltwater. two types of name which are delta and terraces
whats delta kames
- some are formed by en-glacial streams emerging at the snout of a glacier. they lose energy at the base of a glacier and deposit their load.
- others are the result of supraglacial streams depositing material on entering ice marginal lakes. some also form as debris filled crevasses which collapse during ice retreat.
what’s an esker
eskers are ridges made of sands and gravels, deposited by glacial meltwater flowing through tunnels within and underneath glaciers, or through meltwater channels on top of glaciers. Over time, the channel or tunnel gets filled up with sediments. As the ice retreats, the sediments are left behind as a ridge in the landscape.
what does outwash tend to be
- generally smaller as meltwater typically have less energy than glaciers and so only carry finer material
- smooth and rounded due to contact with water and attrition
- sorted, largest material found up valley and smaller working down
- stratified, vertically with distinctive seasonal and annual layers of sediment accumulation in many of the landforms
whats an outwash plain (sandur)
Outwash plains (sandur) are formed in front of a glacier and are where material is deposited over a wide area, carried out from the glacier by meltwater. Discharge occurs from both the melting snout of the glacier and the emergence of meltwater streams from within the body of the glacier. The finest sediments are carried further away from the glacier. Coarser materials are deposited nearer to the snout of the glacier as the meltwater drops these first as its energy declines.
whats a periglacial environment
- with permafrost
- with some seasonal temp variation where the mean temp for at least some period in the summer rise up to 0oc
- where freeze thaw cycles dominate the landform creating processes
- distinctive ecosystems adapted to periglacial environment
whats permafrost
permenentaly frozen ground where soil temps have remained below 0oc for at least 2 years
whats continuous permafrost
summers so cold theres only a very superficial surface melting of the ground.
whats discontinuous permafrost
found if slightly warmer areas so there are islands of permanently frozen ground separated by small pockets of unfrozen less cold areas
whats sporadic permafrost
found when annual temp is just below 0 and the summer temp reach serval degrees above but isolated pockets of permanently frozen ground remain below the surface
whats the active layer
summer temps sufficient to melt the surface layer of permafrost. this layer can be very mobile. it varies in thickness depending on latitude and vegetation cover.
talik
any unfrozen material within the permafrost zone
name periglacial proceses
- freeze thaw action
- nivation
- frost heave
- solifluction
- groundwater freezing
- ground contraction
whats freeze thaw action
- water enters cracks in the rocks and then freezes. ice occupies more space then water and therefore exerts pressure on the crack
whats nivation
hollows form under the emerging glacier as a result of the freeze-thaw cycle and mass wasting. Over time these may enlarge and start to form corries.
whats frost heave
the upward movement of soil due to the growth of lenses of ice in the soil. The lenses grow due to capillary movement of water in the soil.
whats solifluction
the gradual movement of wet soil or other material down a slope, especially where frozen subsoil acts as a barrier to the percolation of water.
whats groundwater freezing
turns groundwater to ice that in turn increases soil stability by creating a frozen soil wall around an excavation or soil zone. It is a versatile method for temporary ground improvement or to provide a groundwater cut-off.
whats ground contraction
happens when the active layer above continuous permafrost freezes and contracts. The following process occurs: Cracks open up in the soil and fine sediments of the active layer and continue down into the permafrost layer.
what are pingos
- dome shaped hills that are commonly up to 500 meter in diameter and up to 50 meters in height
- these land features are common in periglaical areas that are characterised by permafrost and a seasonally changing active layer.
- at the core of the pingo is an ice lens of varying size and the surface layer is made of soil often topped with vegetation.
how do pingos form
when water pushed down from frozen lake sediments accumulates at depth, freezes and then expands again, causing the ground surface to dome.
what are open system pingos
- occur in the valley bottoms and in areas of thin or discontinuous permafrost
- found in east Greenland
- when the surface freezes water is trapped in the talk.
- this water comes under pressure and may move towards the surface where surrounded by permafrost it freezes into an ice core. this causes the surface to dome upwards. as water under pressure finds it way to the surface ice dome and thus pingo, continues to grow
what are closed pingos
- generally found in lowland areas where permafrost is more continuous
- often form on the sites of small lakes
- as these lakes fill with sediments from meltwater, the surrounding permafrost advances and squeezes the unfrozen sediments below the lake
- then the lake its self is frozen the water underlying sediments causes the surface to dome upwards creating the pingo
- if the dome cracks the ice core may melt leading to a collapse of the pingo and a pond forming in the central crater
whats an ognip
talking about a pingo: when temps rise and the ice core thaws. when this happens the top of the dome collapses, leaving a rampant surrounding a circular depression called an ognip
whats patterned ground
the collective term for a number of fairly small sale features of periglacial environments.
