Question 5 of 7: Glacial Geology

Question 5: Glacial Geology (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(a) Small glaciers in mountainous terrain are alpine (mountain) glaciers (i). Large-scale ice masses covering vast areas of land are ice sheets (continental glaciers) (ii). Floating, land-attached coastal ice masses are ice shelves (iii). Tongues of ice flowing outward from an ice cap are outlet glaciers (iv). Piedmont glaciers occupy broad lowlands where advancing valley glaciers spread out into a broad sheet (v).

(b) (i) Glacial budget – the annual balance between accumulation (snow/ice gain in the upper zone) and ablation (melting/sublimation/calving loss in the lower zone); a positive budget makes the glacier advance, a negative budget makes it retreat. (ii) Rock flour – very fine, silt-sized rock powder produced by glacial abrasion of bedrock, which gives glacially-fed streams and lakes a characteristic milky or turquoise colour. (iii) Col – a low, saddle-shaped pass in a mountain ridge, formed where two cirques on opposite sides of an arête erode headward until they intersect and breach the divide. (iv) Valley train – a long, narrow belt of stratified glacial outwash (sorted sand and gravel) deposited by meltwater streams extending down-valley beyond a glacier's terminus or end moraine.

(c) (i) False – that describes Antarctica (≈90% of world ice, ≈70% of fresh water); Greenland holds a much smaller share (≈10% of world ice). (ii) False – ordinary glacier flow is centimetres to at most a few metres per day; tens of metres per day only occurs during rare surge events, not as a general statement. (iii) True – striations (scratches) cut into bedrock by embedded debris parallel the direction the overriding ice moved. (iv) True – both are subtypes of end moraine: terminal marks the glacier's maximum advance, recessional marks a temporary standstill during retreat. (v) False – a mound-shaped body of ice-contact stratified drift is a kame; an esker is instead a long, sinuous ridge deposited by a subglacial or englacial meltwater tunnel.

(d) Forest cover shades and insulates the ground and its organic duff layer, keeping summer ground temperatures low. Removing the trees exposes bare soil to direct solar heating and removes that insulating layer, so more heat penetrates the ground each summer. This deepens the active layer and can initiate thaw of the underlying ice-rich permafrost, causing ground subsidence and differential settling (thermokarst), altered drainage/ponding, and potential damage to any foundations, roads, or pipelines built on it.