Lecture 8 - glacial sediments

Question 1

Marren (2005)

Answer 1

Proglacial streams have a variety of sources and variable discharges
- typically braided w/ high mag low frequency events

Jokulhaulps = large flood bars, mid channel Jokulhaulp bars, hyper concentrated flow, large gravel dunes, ice-block kettle hole structures and rip up clasts

Sandar = range of sources and variable discharges

MW and sediment input volume and character fluctuate in response to climate change

Question 2

Benn (1989)

Answer 2

supra glacial = passive transport, non-modified class

Subglacial = active transport, clasts modified (rounded and blockier)

moraine asymmetry correlation to free facies in the valley

Question 3

Matthews and Petch (1982)

Answer 3

class more rounded near the former glacial snout, more angular near the back wall

more rounded = longer transport pathway, more opportunity to reach the base of the glacier and be transported sub glacially

Question 4

Lukas et al (2013)

Answer 4

RA index and measuring of clasts

different transport pathways

ternary diagrams (?)

Question 5

evans (1999)

Answer 5

moraine asymmetry - basin asymmetry and reworking of pre existing regolith or sediments

RA or C40 indicies

passive and active transport pathways

unequal debris supply - leading to the unequal size of moraines

Question 6

Benn and Ballantyne (1994)

Answer 6

C40 and RA indicies

Storbreen glacier - both indices decline down the moraine

active and passive transport pathways

Question 7

Evans et al (2006)

Answer 7

precesses of deformation, flow, sliding, lodgment and ploughing coexist at the base of temperate glaciers, act to mobilize and transport sediment and deposit it

may be deposited as glacitectonically folded and faulted stratified material – texturally homogenous diamicton

subG processes vary spatially and temporally –> may lead to superimposed signatures of transport/deposition

coupled ice-bed system - unlithified subglacial material deformed in response to applied glacier stress, contributing to glacier motion

summaries whole lecture…

Question 8

Evans et al (2006) definitions

Answer 8

glacitectonite = rock or sediment deformed by subglacial shearing but retains some of the structure of its parent bed material

SubG traction till = sediment deposited by a G with sliding over and deforming its bed

melt out till = sediment released by the melting of stagnant or slowing moving debris rich ice

lodgment = plastering of glacial debris from the base of a sliding glacier on to a rigid or semi-rigid by pressure melting or other mechanical processes