Systems and processes Flashcards
Systems
A set of interconnected parts that work together, have a series of stores or components, and have flows bet: open system – has inputs, outputs and both energy and matter can be transferred into the surrounding environment; closed system – energy is transferred into and out of the system, but matter is enclosed. Glaciers as a system: in a perfectly balanced system inputs and outputs would be equal – the size of the system (glacier) would remain constant, however glaciers don’t have balanced inputs of outputs as overtime they grow and shrink in response to temp changes, snowfall, and other factors, the glacial system = open
Glacial budget
The mass balance of a glacier, i.e. the diff bet accumulation and ablation: a positive glacial budget shows accu exceeds abl, so the glacier = advancing (the forward movement of the snout of the glacier following successive years of pos mass balance – during winter seasons); a negative glacial budget shows abl exceeds accu, so the glacier is retreating (the shrinking of the snout of the glacier following successive years of neg mass balance – during summer seasons) – globally, 9 trillion tonnes of glacial ice has been lost in half a century
Accumulation
The top of glaciers are generally higher, meaning there is a larger amount of precipitation (snowfall), and colder temperatures, resulting in the imbalance between inputs and outputs, with a larger input = accumulation, whereby snow/ice builds up (mainly occurs at higher altitudes at the source of the glacier), leads to glacial advance
Ablation
At the snout of the glacier, the altitude in generally lower, resulting in lower precipitation (snowfall) and higher temperatures, resulting in an imbalance between the inputs and outputs, with a larger output = ablation, whereby snow/ice melt, leads to glacial retreat
Example of glacial advance
Hubbard Glacier, Alaska, USA – located southern Alaska, 122km long, 11km wide, ranges from 3,500-6,000 elevation, since measurements began in 1895, has been thickening and steadily advancing into Disenchantment Bay, advancement due to large accu area, snow falls in the basin either melts or flows down to snout causing to steadily grow, with a rate of advancement of 80 ft annually since 1895 and cont to thicken
Example of glacial retreat
Mer de Glace, Rhone Alps, France – located north side of Mont Blanc, 7km long, 0.5km wide, ranges from 1,500-4,200m elevation, been melting slowly for a number of years, research (2014) sugg it may retreat by 1,400m by 2040 has retreated nearly 2.4km since 1850, during the ice age, the Mer de Glace extended from the town of Chamonix (100m altitude), since them the glacier has retreated by 2,300m and thinned a lot, at the Montenvers Station, where tourists can walk down the glacier from, it has thinned by 150m since 1820, during the 1970/80s, a slight cooling led to an advance of 150m, since then glacier has retreated by 500m and thinned at Montenvers Station by 70m
Cold-based glaciers
Found in very cold areas, e.g. Antarctica – their bases usually well below the ice’s melting point, so very little melting, ice is frozen at base of valley, so little movement, hardly any melting at surface either, even in summer, meaning cold-based glaciers don’t cause very much erosion at all
Warm-based glaciers
Occur in milder areas – their bases are warmer than melting point of ice because of heat of friction cause by the glacier moving, or geothermal heat from Earth, ice at base melts, meltwater acts as lubricant, so easier for glacier to move downhill, ice at the surface melts if temperature reaches 0, meltwater moves down through glacier, lubricating even more, lots of movement means lots of erosion
Glacier formation
For glaciers to form there must be a year-round thick mass of snow which becomes compacted to form ice (abundant snow and cool summers help this process). Snow collects in a (nivation) hollow – when summer temperatures are cool, the snow doesn’t melt, mainly occurring on North facing slopes. Over time the weight of the snow compresses the snow beneath forming firn = sintering. Nivation helps this process by melting the snow crystals and re-freezing them into ice. After 20 years of continued accu of snow and firn formation, all the air is squeezed out and glacier ice is formed. Settling of snow = loose, granular consistency; nivation = annual and diurnal temperature changes lead to freeze-thaw alternation, and the conversion of snow to ice crystals; firn or neve = inc pressure between individ grains causing pressure melting to change the loose snow into a dull, white, structureless mass, with far less pore space therefore more impermeable – takes 10 years to form; sintering = cont fusion and squeezing out of air resulting from further compression by the cont accu of snow and ice; glacier ice = blue-ish in colour and containing little air
Weathering processes
Frost action, nivation
Nivation
Processes inv snow and ice causing erosion, commonly due to fluctuating temperatures – nivation hollows formed by niv procs, whereby snow gathers in small dep and erodes via freeze-thaw, mass wasting = begin of corries
Frost-action
Water gets into cracks of rocks, freezes, and so expands by 9%, repeated action builds pressure on a rock, causing it to shatter and break off
Ice movement processes
Internal deformation, compressional flow, extensional flow, rotaional slip, basal sliding
Internal deformation
Occurs due to the pressure of glaciers weight, causing individ ice particles to melt around their edges and one by one the particles slip forward on the thin film of water and immediately refreeze and under the inf of gravity, layers of granules in ice slide across each other
Compressional flow
When ice hits a shallower gradient, friction causes the ice to slow down, build up, and compress, causing the ice to get thicker
