GLACIAL SYSTEMS
Glaciers are dynamic systems:-
You need to know about the occurrence of glaciers today and in the past, also globally and in the UK.
They are Dynamic Systems (input, outputs, stores and transfers) in several different types...Ice Sheets, Ice Caps, Ice Shelves, Valley Glaciers, Cirque Glaciers, Piedment Glaciers.
4 main advances in Quaternary...Anglian glaciation (425 000 and 380 000 years ago), Wolstonian Glaciation (175 000 and 128 000) Devensian (26 000 and 15 000 max 18 000), most recent (12 000 and 10 000) the Loch Lommond re-advance in W. Scotland
You need to be able to decide if a glacier is advancing or retreating or is stagnant ..using budgets, the significance of firn line/snow line should be recognised. (rmember a glacier can still be moving forward even if it is in retreat!)
firn/neve line = snow that survives in summer (density 90.4 g/cm-3) this eventually becomes glacial ice (0.83 to 0.910 - which takes between 30-40 years to 1000 to do) this is known as diagenesis.
(terminology to revise ...zones of accumulation, zone of ablation, divided by the firn/equilibrium line
....annual budget = net accumulation (growth) ...advance
= net ablation (loss) .... retreat
= equilibrium (stable) ... no change - stagnant
Why do glaciers move? - gravity, gradient, thickness of the ice, internal temperature of the ice, the glacial budget ( a positive budget)
How do they move - solid/rigit = brittle and cracks, but under pressure it is like a plastic and so 2 areas
upper zone = brittle and breaks
lower zone = under pressure - deformation
eg Mer de Glace in French Alps 1842 -sides and base flows slower (frozen onto floor and sides) than top and middle.
COLD (POLAR) - High mid-latitude, low relief basal temp. below pressure melting point, slow rates of movement (few metres/ year), = Arctic, Greenland
WARM (TEMPERATE) - High- altitude,steep relief,basal temp. at or below the pressure melting point, rapid movement (20-2000m/yr)
MECHANISMS OF MOVEMENT = BASAL SLIDING (SLIPPAGE, CREEP OR REGELATION, BED DEFORMATION)
Franz-Josef New Zealand (300m/yr by basal sliding) Salmon Glacier in Canada
(45% -90%)
= INTERNAL DEFORMATION (INTERGRANULAR FLOW, LAMINAR FLOW)
Meserve glacier in Antarctica (3-4m at its firn line and 100% internal deformation)
EXTENDING FLOW (STRETCHING) AND COMPRESSING FLOW (THICKENS)
PROCESSES-
= internal (eg creep and fracture), basal (such as sliding, slippage and enhanced basal creep), extending and compressing flow and how surges impact on movement.
= Differences in rates of movement across the surface, width and depth.
= Temp. profiles of cold and warm glaciers and how movement, and processes will be affected in these areas.
GLACIAL CONDITIONS PRODUCE CHARACTERISTIC LANDFORMS OVER A WIDE AREA
PROCESSES
EROSION = Plucking and Abrasion, freeze thaw,etc
WEATHERING = Frost action and Dilation nivation, etc
TRANSPORT =Supra- ,En-, and Sub-glacial, etc
DEPOSITION = Logement and ablation, etc
Where/when/why these processes take place...
Factors influencing rates including, temperature, ice thickness, nature of the bedrock and the character of the debris transported....
Rates of abrasion (presence of basal degris, debris size and shape, relative hardness of particles and bedrock, ice thickness, basal water pressure, sliding of basla ice, movement (supply) of debris to the base of the glacier, removal of fine debris - these then vary spatially and temporally)
YOU SHOULD BE ABLE TO DESCRIBE AND EXPLIAN THE FORMATION OF LANDFORMS AND THE DEPOSITIONAL LANDFORMS (ALONG, AND BEYOND THE GLACIER) PLUS AN ANNOTATED SKETCHES AND AT LEAST ONE LOCATED EXAMPLE FOR EACH (EG LAKE DISTRICT, ICELAND, ARRAN, MATTERHORN - PYRAMIDAL PEAK IN SWITZERLAND, STRIDING EDGE -ARETEI IN LAKE DISTRICT) Their impact on human activity - both positive and negative.
Terminology Cirques (corries, cwms) Aretes, pyramidal Peaks, troughs, trunkated spurs, hanging valley, Crag and tail, Roches Moutonnee, etc.
FLUVIO-GLACIAL AND PERI-GLACIAL AREAS HAVE DISTINCTIVE LANDFORMS-
Glacial deposits are generally unsorted, angular and unstratified. This material may have a common orientation of elogated particles (remember Arran exercise)
Fluvio-glacial deposits are generally sorted, rounded and stratified.
(remember as above for each landform.... able to describe, explain, sketch,know an example and human impact )
Terminology - Depositional landforms = moraines (push, terminal, recessional, lateral, medial, ground) Till (logement and ablation till), till sheets, drumlins, erractics.
- Fluviglacial - erosional landforms = Meltwater channels, overspill channels (Scotland , where trains use these gaps through the mountains), Sichelwannen (crescent shaped scratches on the side of the valley formed by englacial meltwater streams that tough the side), Tunnel valleys (eroded by subglacial streams then infilled seen in E. Anglia =Stour Valley at Long Melford)
- depositional landforms = Outwash (sandur, eg Iceland =Gigjokull and Solheimajokull) Varves found at the bottom of proglacial lakes - summer lots of large sediment available while in winter only a little amount of small sediment so banding a pair of bands = one year). Kettle holes for dead ice around Ellesmere in Shropshire or Solheimajokull , Eskers can be beaded in Dublin, Delta Kames, Kame terraces, Braided streams
Know the part played by the flowing processes WEATHERING, MASS MOVEMENT, FLUVIAL, WIND and GROUND PROCESSES ... located in areas like Alaska, Iceland etc.
Periglacial processes and landforms
permafrost ( continuous, discontinuous ...talik and active layer ...the area in upper part of ground that thaws for the summer,) sporadic seasonal temperature variations, freeze thaw cycles,distinctive flora and fauna, pingos (open system pingos in Greenland, and closed system pingos in Canada ...then when ice core melts the dome collapses leaving a rampart, surrounding a cirular depression = ognip in Ireland and Llanberis in N. Wales, Patterned ground from frost heave, forst push and pull = stone polygons found in Barrow in Alaska, stone garlands, stone stripes, Ice wedge polygons due to ground contraction found near Oxford, Solufluction (lobes ...asymetrical in cross-section like in the Cheviots, then in S. Britain material left by Solufluction is known as head around Portland.
Dominant processes = freeze thaw weathering ..scree slopes, rockfalls, blockfields or felsenmeer = sea of rocks.
= water ..Braided streams
= aeolian ...loess in Germany, Siberia and China
Impact of erosional landforms on human activity
Transport, agriculture, industry, settlement and tourism (eg keswick)
Impact of depositional landforms on human activity
Valley floors. larger flatter floors and expanses, high rain and drumlins = poor drainage, ribbon lakes formed by moraine - lake district.
Impact of fluvioglacial landforms on human activity
outwash deposits = poor infertile soils, but Kame terraces are often good for transport links above flood plains
SYNOPTIC LINK
GLACIATED AND PERIGLACIAL AREAS OFFER OPPORTUNITIES AND CHALLENGES FOR HUMAN ACTIVITY
Emphasis on human activity rather than processes ..ie the ability to overcome the challenges in order to exploit the opportunities (capital, technology and knowledge)
Periglacial and permafrost environments (as above)
links with information on Settlement, Agriculture and Development
Upland glaciated areas = inaccessible and environmentally fragile environments, marginalised and neglected by political and economic decision making, because of low population and inaccessiblity, poor, peripheral and remote ...physical constraints (challenges) = extreme climate,steep slopes, thin soils, inaccessibility
...human constraints = low population, low electoral importance, vulnerability to economic change.
These societies = few people,dependence on natural resources, limited educational opportunities, limited job demand, absence of urban commodities..have only 10% of worlds pop.
QUESTIONS
a) What do you understand by the periglacial? (5)
b) Examine the role of freeze-thaw cycles in the formation of periglacial landscapes. (20)
a) How might the glacial mass balance of the glacire in figure 3 (not included in this page) affect its movement? (5)
b) Explain how the movement of a glacier produces distinctive landforms. (20)
a) Outline the main characteristics of periglacial environments (5)
b) Account for the range and variety of periglacial landforms. (20)
a) distinguish between the erosional processes of abrasion and plucking. (5)
b) Examine the impact of processes of glacial erosion on the landscape. (20)
a) Explain the difference between accumulation and ablation. (5)
b) Describe the glacial system and examine how variations within this system influence the rate of movement. (20)
a) What is glacial mass balance? (5)
b) Explain how the movement of a glacier produces distinctive landforms. (20)
a) Describe Till fabric analysis (5)
b) Glacial and fluvio-glacial landforms have distinctive characteristics. How might field evidence be used to distinguish them apart? (20)