Question 7 of 9: Glacial Deposits

Question 7: Glacial Deposits (10 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.

1) Till / ground and terminal moraine. Composition: unsorted, unstratified diamict – a chaotic mixture of clay through boulder-size clasts, often striated/faceted, with no bedding. Landform shape: broad, hummocky, low-relief blankets (ground moraine) or arcuate ridges marking a still-stand or readvance of the ice margin (terminal/end moraine). Creation: material entrained within or beneath the moving ice (by plucking and abrasion) is carried and then simply released/bulldozed as the ice melts or stalls – no meltwater sorting is involved, so grain sizes remain jumbled.

2) Esker. Composition: well-sorted, stratified sand and gravel, often cross-bedded, showing the current-bedding structures typical of stream deposition. Landform shape: a long (up to tens of km), narrow, sinuous ridge that winds across the landscape independent of present-day topography, tracing the former course of a subglacial/englacial meltwater tunnel. Creation: pressurized meltwater flowing in a tunnel within or under the stagnant/melting ice deposits its sediment load inside the ice-walled channel; when the surrounding ice melts away, the channel-fill sediment stands as a positive-relief ridge.

3) Kame (or kame terrace / outwash plain, sandur). Composition: sorted, stratified sand and gravel (like an esker, but deposited in a different setting – ponds or channels on, in, or against the ice, or braided-stream outwash beyond the ice front). Landform shape: an irregular, isolated mound or hummock (kame), a terrace-like bench along a valley wall (kame terrace), or a broad, gently sloping, braided-stream apron beyond the ice margin (outwash plain/sandur). Creation: meltwater deposits sediment in a supraglacial or ice-marginal pond, crevasse, or channel; when the ice support melts away, the deposit collapses/settles into the irregular kame form, while outwash-plain material is simply braided-river sediment reworked beyond the ice front and is comparatively well-sorted with a clear down-current fining trend.