Glaciated landscape development Flashcards
Causes for present distribution of cold enviornments
Latitude, altitude, aspect, relief, distance from moisture source
Latitude
The higher the latitude, the less solar radiation (solar angle) it receives so the colder it is
Altitude
The higher the altitude, the lower the temperature due to lower air density, typically for every 1,000m climb in alt, temperature decreases by 6; altitude and latitude work tog to create a broad range of glacier locations around the world (e.g. Mt Kilimanjaro closer to the equator, although at higher altitudes)
Aspect
The direction a slope faces, in the Northern hemisphere, glaciers are more likely to form if they face North or East as it received less sunlight energy through the day, so high chance of accu and pos mass balance
Relief
Shape or slope of the terrain/land, if the slope is too steep, it may prevent ice accumulation as the ice/snow may just slide off rather than build up
Distance from moisture source
Glaciers and cold environments need precipitation in the form of snowfall to develop, precipitation is more likely to occur near a moisture source (e.g. sea/ocean) rather that ‘continental interiors’
Causes of ice age
Milakovitch cycles, plate tectonics
Milankovitch cycles
Variations of the tilt/orbit of the Earth around the sun causing the Earth’s natural warming and cooling periods (for all Milankovitch cycles, the av change occurs over 100,000 years):
- Shape of the Earth’s orbit (eccentricity) = changes from circular to elliptical in a cycle, cycle lasts bet 90,000-100,000 years (needs most extreme elliptical shape)
- Planet tilts on axis (obliquity) = tilt of Earth on its axis varies bet 22.1 and 24.5, when tilt angle is smaller, summers and winters differ less in temperature, cycle lasts 41,000 years (needs to be 22 tilt so the summers are cold and snow/ice doesn’t melt)
-Earth wobbles on its axis of rotation (precession) = at one extreme of the ‘wobbles’, the Northern hemisphere points towards the sun, when it is furthest form the sun, resulting in warmer winters and colder summers (needs to be on axis closest to sun in winter so summers stay cool);
Plate tectonics
Large volcanic eruptions can alter the climate, dust can sit in the atmosphere preventing sun rays reaching the Earth’s surface, cooling it (alongside Milankovitch cycles)
Causes of climate
Low levels of insolation, coolness of air, high pressure systems, high albedo, katabatic winds
Low levels of insolution
Sun remains at low level in the sky, so even though there is cont sunlight it covers a wide area causing a lack of sun, warmth
Coolness of air
Holds low levels of water vapour, little more powdery snow
High pressure systems
The frontal system rarely penetrate polar areas giving low levels of precipitation
High albedo
In areas of constant snow much on the incoming solar radiation is reflected
Katabatic winds
Masses of cold, dense air flow down valleys and off upland, exceed 200km per hour as no obstacles
Erosional landforms
Corries, aretes, glacial troughs, hanging valleys, truncated spurs, roches moutonnee
Corries
An amphitheatre-shaped depression in a mountain side, with a steep back wall and a rock lip – form when snow cont to build up in a dep or nivation hollow, compacting to form a glacier, ice movement = rotational slip, back wall eroded through plucking and frost action, and hollow deepened through rotational abrasion (tarn = small, deep circular lake in corries that stays there after deglaciation due to the rock lip – form as over deepening by abrasion by sub glacial debris moving in rotational slip)
Aretes
Narrow, knife-edged ridge – form when 2 corries cut back towards each other, pyramidal peak = pointed peak where 3 or more corries meet at a point
Glacial troughs
U-shaped valley with steep vertical sides and flat lateral bottom – form by a glacier bulldozing and eroding through a river (V shaped) valley with enough energy to erode away the river’s interlocking spurs, leaving smooth but steep truncated spurs on the valley side and a wide, flat valley floor (ribbon lake = long, narrow lake in glacial trough – form as extending or compressing flow over deepens parts of valley floor)
Hanging valleys
Small valleys above main glacial trough that often have waterfalls lowing off vertical cliffs at the end with a tributary glacier left high above the main valley – forms as glaciers in the tributary glacial valleys would have been smaller, containing less ice, and so eroding less than that in the main valley, consequently the floor of the tributary valley was left higher than that of the main valley when the ice retreated
Truncated spurs
Steep, cliff-like valley sides – forms when the valley is occupied by ice, the glacier truncated the tip of the interlocking spurs, leaving behind steep cliffs
Roches moutonnee
Asymmetric bedrock hills with gently sloped stoss with striations and blunt jagged lee – form whereby a mound of rock is shaped by a glacier flowing over and eroding it, as the glacier hits an obstacle that is too large and hard to pluck, so it must move over it, the glacier inc pressure and friction, therefore inc melting (as lower ice can reach pressure melting point), meltwater allows glacier to slide over rock: smaller rocks abrade the stoss side when glacier meets mound, when the glacier reaches the top of the mound, friction and pressure drop causing meltwater to refreeze causing frozen rocks to be plucked from the lee side
Depositional landforms
Drumlins, erratics, moraines, till plains
Drumlins
Streamlined hillock, commonly elongated parallel to the former ice flow direction, composed of glacial debris and sometimes having a bedrock core, formed beneath an actively flowing glacier, variable size: typically 30-50m in height and 500-1,000m in length, and often occurring in swarms – form when a glacier hits an obstacle that cannot be eroded, deposition from underneath the glacier builds up behind the obstacle, the glacier moves over the other side causing a tear drop shape with a long, tapered edge, whereby the blunt end is the stoss side and the tapered end the lee side
Erratics
A boulder or large block of bedrock that is of diff rock type to surrounding rock – boulder broken off by weathering and erosion and transported away from source by a glacier and deposited when the glacier loses energy
Moraines
Landform developed when debris carried by glacier is deposited: lateral moraine – debris deposited along the side of a glacier comprising both rockfall debris from above and debris from ground up by ice-marginal processes; medial moraine – a distinct ridge of debris occurring on the surface of a glacier where two streams of ice merge; terminal moraine – a prominent ridge of debris formed when a glacier reached it maximum limit during a sustained advance; recessional moraine – a ridge of debris representing a stationary phase during otherwise a gen retreat; push moraine – a complex landform from a few metres to tens of metres in height comprising of assorted debris that has been pushed up by a glacier during an advance
Till plains
Till = a poorly sorted mixture of mud, sand and gravel-sized material (form through weathering and erosion) deposited directly from glacier ice; till plains = an extensive flat plain of glacial till that forms when a sheet of ice become detached from the main body of a glacier and melts in place, depositing the sediments it carried (ground moraines formed when till melts out of the glacier in irregular heaps, forming rolling hills)
Fluvioglacial landforms
Meltwater channels, kames, eskers, outwash plains, kettle holes
Meltwater channels
Streams of meltwater (melted glacier) due to high temperatures, whereby channels can flow within, in front of, and around the glacier, highly erosive and if lose energy, they deposit sorted material in small islands, creating braided channels
Kames
Conical mounds of fluvioglacial material (sand and gravel deposits) that are often stratified and sorted, left when meltwater flows into a lake dammed up in front of the glacial snout by recessional moraine deposits: kame terrace – flat-topped mound found along the side of the glacial valley, deposits of meltwater streams flowing between ice and valley sides, gen better sorted than other kames; kame delta – mounds formed on the valley floor as a meltwater stream enters a marginal lake, smaller than kame terraces and when the ice retreats further, the delta kame often collapses; crevasse kames – occur as meltwater streams enter the glacier through surface crevasses, material is then deposited on the valley floor under the glacier forming a small hummock
Eskers
Long ridges of sand and gravel that follow the path of the original meltwater channel, sediment is deposited when the subglacial stream loses velocity, whereby the mound retains its shape due to the high hydrostatic pressure
Outwash plains
Formed in front of the glacier, where material is deposited over a wide area, carried out from the glacier by meltwater, whereby discharge occurs from both the melting snout of the glacier and the emergence of meltwater streams from within the body of the glacier, in which finest sediments are carried further away from the glacier and coarser materials deposited nearer the snout of the glacier as the meltwater drops these first as its energy declines (deposits may create alluvial fans = smaller, fanned out sections, whereby the meltwater channels separate to take the fastest route through the deposited material)
Kettle holes
Depressions in the ground often containing water – form as glacier retreats, may leave large blocks of buried ice, which slowly thaws over time and covering gravel collapses leaved a dep, if deep enough to tap water table, kettle hole lake forms
Periglacial landforms
Patterned ground, ice wedges, pingos, blockfields, solifluction, lobes, terracettes, thermokarst
Patterned ground
Frost heave happens when water underneath stones freezes and expands, forcing stones upwards – ice lenses exist within permafrost, they grow through repeated frost action, capillary action draws more water to the ice lens causing it to grown more, when the ice expands stones around the ice lens are shunted upwards, larger storms roll down to the edge of the mound due to their weight, forming circles around them, which form polygons where close together or if mounds are on a slope, stones roll downhill forming stone lines
Ice wedges
Downwards, vertical, narrowing masses of ice that are bet 1m+ wide at the base and extent below the ground surface usually 3m deep (up to 10m), frost contraction causes cracks to form in the permafrost when temperatures drop very low in winter, when temperature inc in summer the active layer thaws and meltwater seeps into cracks, the permafrost layer is frozen, so the water in the cracks freezes forming an ice wedge, this process repeats through winter and summer in following years, widening and deepening the ice wedge, from above called ice wedge polygons (diff to stone polygons)
Pingos
Conical hill with a core of ice, can be up to 500m wide, 50m high, centre often becomes concaved in the centre when the ice core melts: open-system pingos – form when there’s discontinuous permafrost, groundwater forced up through gaps bet areas of permafrost, water collects tog and freezes forming a core of ice that pushes the ground above it upwards, usually found in valley bottoms in Greenland, Alaska, closed-systems pingos – form in areas of continuous permafrost where there’s a lake at the surface, lake insulates the ground so the area beneath remains unfrozen, when lake dries up ground no longer insulated and permafrost advances around the area of unfrozen ground, causes water to collect in the centre of the unfrozen ground, water freezes and creates a core that pushed the ground above it upwards
Blockfields
Surfaces covered by rock rubble derived from weathering of the underlying but largely hidden bedrock, expanses of loose rock formed by frost shattering from repeated freezing and thawing, formed in mountain regions that have (had) mod periglacial climate
Solifluction lobes
(See permafrost)
Terracettes
Vegetation interrupts soil moving down a slope due to frost creep, solifluction, causing a slatter area to build up behind the obstruction, leading to a series of step-like terraces
Thermokast
Depressions in the ground surface creating an uneven, marshy landscape, ice in the ground, e.g. pingos, ice lenses melt, causing the ground to collapse and holes to form, which fill with water
