Landform-sediment assemblages of surging glacier margins in
1982-83 surge of variegated glacier of
Thrust block & Push Moraines
Thrust block moraines – composite ridges & hill-hole pairs
Two ice-marginal settings
- Margins of surging glaciers
- Sub-polar glacier margin in permafrost region
Proglacial thrusting – rapid advance into proglacial sediments
(seasonally frozen, unfrozen & contain discontinuous permafrost)
Proglacially thrust unfrozen materials
Surge margins of Icelandic glacier Bruarjokull & Eyjabakkajokull
Thrust block Moraines – constructional feature produced by surging glacier, sufficient sediment available for glacitectonic thrusting, folding & stacking
Over ridden thrust block moraines
Ice moulded hills in the proglacial forelands of Bruarjokull & eyjabakkajokull – down ice of topographic depressions from which the hills were displaced by thrusting
Surface features – fluted/ Drumlinized
Internal structure – glacitectnized outwash or lake sediments, tops of which modified intoglacitectonite
Ice-moulded hills – overridden thrust block moraines
Thrust block moraine demarcates the former glacier margin during a surge
Prolonged period of modification by over-riding ice – thrust block moraines resemble cupola hills of Aber
Concertina Eskers
Sinuous Eskers and concertina plan-form eskers
(Knudsen) – Concertina eskers are produced by shortening of pre surge, sinuous eskers, deformed by extreme tectonic activity
Vertical thickening – concertina plan form
Crevasse – squeeze ridge
Bruarjokull & eyjabakkajokull,
Trapridge Glacier & donjek Glacier – in
Tectonics experienced during surge – glacier is highly fractured & crevasses may extend to the glacier bed
Flutings
Forelands of many glaciers
Evidence of rapid advances over substantial distances foreland of Bruarjokull (regularly spaced parallel sided flutings)
Numerous boulders with short sediment prows/ flutes on their down-flow sides interpreted as ploughs/ incipent flutes produced by boulders embedded in glacier sole
Elongation of these flutes suggest, formed during a single flow event when basal water pressures & degree of ice-bed coupling remained shorter & much less uniform in long section
Flutings & crevasse squeezed ridges – aspect & subglacial geomorphology of surging glaciers
Thrusting/ squeezing.
Zone of thrusting in the snout, lifted from the bed thrusting in surging glaciers
Supraglacial sediments
Low relief hummock moraine comprising inter bedded sediment gravity flows & crudely bedded sediment sediments – small ridges, thrust intersected the bed
Hummocky moraine
Subsequent ice-stagnation of widespread & effective transportation of large volumns of material
Lowland surging glaciers – thrusting is dominant process in transporting large volumns of debris-rich stagnant ice preserved from a previous surge, producing thick sequences of debris rich & debris-covered ice in surging snout
Landform assemblage – Hummocky moraine
Kettle & kames Topography
Differential form of overridded thrust block moraine by extensive evidence of on going meltout of buried ice
Ice-cored outwash & glacilacustrine sediments
Variegated glacier surge – outbursts of supraglacial water
Landform model for surging glacier
Based on combination of observations from contemporary surging glacier margins & published literature
Geomorphic & sedimentological signature of surging
Geomorphology – 3 overlapping zones
· Outer Zone: of thrust block & push moraine
Weakly consolidated pre-surge sedimets
Structurally – major thrust block moraine restricted to topographic depression, large enough to collect sufficient sediment during the quiescent phases.
· Intermediate zone (zone B) – patchy hummocky moraine located on the down-glacier sides of topographic depression, dumped on ice proximal slopes of thrust block & push moraine.
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