Cold - KQ1 (processes and factors giving cold environment their distinctive characteristics) Flashcards
What are the three types of cold environments?
- Glacial/polar
- Periglacial
- Mountainous
What are glacial/polar characteristics?
EXAMPLE = Ambleside, Lake District
- Snow and ice all year
- Very cold and dry
- -60C to 10C on coast
- Winter temperatures = -70c to -25C
- Summer temperatures = -40C to -2C
- Katabatic winds form as dense cold airs over central plateau drains into valleys
What are kebatic winds?
Cold mountains winds - dense air flows down from the mountains to the lowlands, chilling the ground as it passes over
What are periglacial characteristics?
EXAMPLE = Tromso, Norway
- Significant cover of snow and ice but not all year round
- Found in areas of high altitude or high latitude
- Large seasonal temperature ranges
What are mountain characteristics?
EXAMPLE = Verkhoyanks, Syria
- Once covered in ice
- Landforms which were formed during cold periods continue to exert and influence over how local people live
What are the reasons for cold climates?
- High altitude
- Winds
- Albedo
- Mountain environments
Why do high altitudes make cold climates?
- Incoming solar radiation is spread out over a greater area at poles = heating is less intense
- High altitudes = less solar radiation = more is lost as it passes through greater distance in atmosphere = scattering and reflection
- Equator is shorter distance from sun = less incoming solar radiation lost
- Polar night = sun does not rise at all so no heat for long time periods
- Lower pressure (less oxygen, nitrogen and carbon dioxide as altitude increases) = molecules are further apart = less kinetic energy = less heat
Why do winds make cold climates?
- Difference in air pressure between air masses causes winds
- Blow from high pressure to low pressure (controlled by pressure gradient)
- In cold = sinking cold dense air can flow rapidly downslope which cools land surface
Why does albedo make cold climates?
Albedo = measure of how reflective a surface is (out of 1 like probability)
- High albedo = reflect incoming solar radiation = stays cold
- Fresh snow = 0.9 so only 0.1 units of solar energy is absorbed
- Arctic sea and Antarctic ice mass and ice shelves all reflect incoming solar radiation
Why do mountain environments make cold climates?
- Often lie between 45 and 60 degrees north of equator (eg Lake District) = at junction between two types of air (cold polar air north and warmer tropical aril south)
- Mixing air masses = uplift of warmer air along junctions = produces unstable, bad weather with rain (especially in winter)
How do glaciers move?
1 - Internal flow/deformation = movement within glacier due to gravity stresses
- Where ice crystals orientate themselves in direction of glacier’s overall movement = may slide past each other
- Results in crevasses within and at surface of ice
2 - Basal slippage = sliding effect of a glacier over bedrock by regelation slip/creep
- On upper side of obstacle = increasing pressure in lower ice = pressure melting locally
- Meltwater allows ice to slip over obstacle but then refreezes in lower pressure conditions on downglacier side of obstacle
How do glaciers erode?
- Abrasion
- Plucking
- Bulldozing
How does abrasion erode glaciers?
- debris trapped in sides and base of ice abrades/scratches bedrock = broken down into finer debris (rock flour at glacier snout)
- Abrasion evidence = shown by striations (scratch lines) left on rocks of deglaciated areas
How does plucking erode glaciers?
- Melting and refreezing of water around obstacles and rocks in bed of glacier
- Upstream of obstacles = high pressure = lowers melting point = melting
- Downstream = lower pressure = ice refreezes and plucks loose rocks from bed of glacier as ice moves downstream
- Can form landforms known as Roche Mountains
How does bulldozing erode glaciers?
Pushing already weathered rock debris
What are factors affecting erosion?
- Speed of ice (faster = more erosion)
- Temperature of lower ice (below freezing = sticks = little erosion)
- Basal water (water at base of ice = slides = little erosion)
- Ice thickness (thicker = more = more weight)
- Debris particle size and shape (large angular = more erosion)
- Amount of meltwater (more = less erosion = lifts up glacier off bed so rocks in ice and bedrock are not in contact)
- Bedrock (soft = more erosion)
What are the processes of weathering in cold areas?
- Freeze thaw
- Dilation
- Carbonation
How does freeze thaw cause weathering in cold areas?
- Ice melts during day and gets into cracks and joints
- Freezes at night and expands by 9% = exerts pressure on rock = crack gets bigger
- Repeated process = rock will break away
How does dilation cause weathering in cold areas?
- Weight of glacier ice = pressure on underlying bedrock
- At end of glacier or snout (seasonal changes) = ice melts and pressure is released
- Bedrock expands and cracks
How does carbonation cause weathering in cold areas?
- CO2 dissolves quicker in cold water = meltwater streams carry weak carbonic acid
- On carbonate rocks (eg limestone) carbonate ions are attacked by acid and dissolve = forms bicarbonate ions which are carried away by meltwater
What are factors affecting weathering?
- Rock type (harder = less)
- Altitude (higher = higher pressure = more)
- Time of day (colder = more carbonation // night = more freeze thaw)
- Temperature
What are the landforms of glacial erosion?
- Cirques/corries
- Arêtes
- Glacial troughs
- U-shaped valleys
- Truncated spurs
- Ribbon lakes
- Hanging valleys
- Fjords
What are corries/cirques?
EXAMPLE = 2 glacial cirques behing Mounth Tjamuhas in Abisko National Park, Sweden
- An arm-chair shaped landform
- Formed by various forms of erosion
- Surrounded by steep ridges and almost vertical headwall
- A rock lip is present which hold back the lake (or tarn) at base of landform
How do corries/cirques form?
- Snowflakes collect in a hollow = compressed and air is squeezed out to become firn or neve (by nivation)
- Pressure from more layers of snow = firn becomes glacier ice over 1000s of years
- Erosion and weathering by abrasion, plucking and freeze thaw = hollow is bigger
- Ice is trapped in hollow and cannot move downhill = gravity still tries = rotational slip = causes ice to pull away form from back wall creating crevice or bergshrund
- Plucked debris from back wall = further erosion through abrasion = deepens corrie
- Some debris deposited at edge of corrie = builds lip
- Create rounded, armchair shaped hollow with steep back wall
- When ice in corrie melts, circular lake is often formed at bottom of hollow (called tarn)
What is an Arête?
EXAMPLE = Striding edge, on mountain of Helvellyn in Lake District
- Formed when two neighbouring corries run back to back
- As each glacier erodes either side of the ridge edge becomes steeper and ridge becomes narrower
How are glacial troughs/u-shaped valleys formed?
- Channelling of ice through valleys and erosion
- Before glaciation = active freeze thaw weathering under periglacial process weakens floor and sides of valley = preparation for rapid erosion during glaciation
- During interglacial periods periglacial processes return and weaken further
- As glaciation occurs ice begins to move (and down valley) deposited material is used for abrasion = created u shape
What is periglacial?
An area either adjacent to a glacier or subject to repeated freezing and thawing
What are the periglacial processes?
- Mass movement
- Freeze thaw weathering
- High wind erosion
What are truncated spurs?
- Begin as interlocking spurs
- as glaciation occurs ends of interlocking spurs are eroded through plucking and erosion (lie in the path of oncoming glacier)
- Distructive effect forms truncated spurs
How are ribbon lakes formed?
EXAMPLE = Lake Windermere, Lake District
- Formed when ice extrusion erodes away at the floor of the valley and causes deep rok basin
- Rock basin is eventually filled by precipitation and any meltwater that runs in off the mountain sides
What are Fjords?
EXAMPLE = Sogne Fjord Norway
- Glacial tough partly below sea level
- Forms as any other u-shape valley does (but partly submerged) = cut into more resistant rock
- Often long with great depth (sogne fjord = 1300m) extreme depth = lots of glacial erosion to construct landform
- Sogne Fjord rises as closer to mouth of Fjord on coast
- Suggests erosional power of glacier as it advanced to the seaward end of fjord was reduced = example of how shaped due to glacial erosion
What are the processes/types of deposition?
- Ablation
- Directly from ice (unstratified till/boulder clay)
- Fluvioglacial deposits (meltwater flowing from a glacier = stratified)
- Deposits in front of glacier (proglacial deposits)
What is stratified and unstratified?
Stratified = sorted Unstratified = not sorted
What is ablation?
The removal of material (ice, debris) from a glacier such as melting, evaporation and sublimation
What are the landforms of glacial and fluvioglacial deposition?
- Till plains
- Drumlins
- Moraines
- Varves
- Esker
- Kames
What are till planes?
EXAMPLE = NW Norfolk
- Mix of clay and stones deposited by glacier
- Formed below a vast ice sheet covering Norfolk
- Deposited during and after ice melted (450,000 years ago) in Anglian Glaciation
What are drumlins?
EXAMPLE = Kendal Drumlins, Lake Districts
- Small low hills in the shape of an inverted spoon
- Blunt end of hill faces upstream direction and tapered end faces downstream in ice movement
How do drumlins form?
- Deposited from moving ice
- Form a swarn or field of a similar size/shape of hills (up to 40m high and 500m long)
What are lateral moraines?
Formed by freeze thaw = above the glacier
Plucking = on valley sides
- Both lead to rocks falling into or onto valley glacial sides
What are medial moraines?
Found at the tributary between two glaciers
What are terminal moraines?
Found at furthest point reached by a glacier when the glacial snout bulldozes material ahead of it
- Formation depends on amount of material carried, rate of movement and rate of ablation (and amount of meltwater)
What are moraines and how do they form?
Terminal, medial or lateral
EXAMPLE = Gorner Glacier, Zermatt, Sweden
- Unstratified deposits of angular rock fragments
How they form:
- When glacial ice melts = different types of rocks that have been carried are deposited forming moraines
What are varves?
EXAMPLE = Lakes in Sweden and Finland
- Layers of silt and sand which were deposited on the floor of a lake in advance of a glacier
- Found in proglacial lakes in ice margins
How do varves form?
- Form from fluvial deposition
- Each varve consists of 2 layers of sediment = fine sand sized particles and another of clay and silts
- In summer = large flows of meltwater deposit thick layers of coarser sediment = bigger flow = more material is transported and deposited (usually fine sand)
- In winter = smaller meltwater flows deposit finer material as lower velocity can only carry finer material (eg clays and silts) = each year = 1 year melting
- Flow of meltwater affects rate of deposition of different sediments
What are eskers?
EXAMPLE = Blakeney Esker, Norfolk
- Long low winding ridge of stratified sands and gravels deposited in meltwater tunnel by meltwater under a glacier or ice sheet
- Rarely well preserved
How do eskers form?
- Fluvial deposition
- Sometimes transported load volume exceeds velocity required = deposition in tunnel = ice melts = eskers appear
- Vary in size from few metres high to 50m high
What are kames?
EXAMPLE = Talkin Tarn, Carlisle, Cumbria
- Mounds of stratified sands and gravels deposited along the front of a melting or stationary glacier, consisting of sands and gravels
How do kames form?
- Talkin Tarn is kettle-hole lake formed by glaciers 10,000 years ago when ice melted and permanent lake is created (water filled in it)
- Fluvial-glacial sediments are washed into lake = stratified deposits forming in and around it (especially as velocity drops = deposition occurs)
