SURGING GLACIER SYSTEM

Landform-sediment assemblages of surging glacier margins in Iceland, Svalbard, USA and Canada

1982 surge of Variegated Glacier of Alaska

Thrust Block and Push Moraine

Thrust Block moraines – composite ridges & hill hole pairs

Two ice-marginal settings

- Margins of surging glaciers

- Sub-polar glacier margins in permafrost terrain

Proglacial thrusting – rapid advance into proglacial sediments

(seasonally frozen, unfrozen or contain discontinuous permafrost)

Proglaciacially thrust unfrozen materal – surge margins of Icelandic Glacier (Bruarjokull & Eyjabakkajokull)

Thrust block moraines – constructional feature produced by surging glacier, sufficient sediment available for glacitectonic thrusting, folding and stacking

Over-ridden thrust block moraines

Ice-moulded hills in the proglacial forelands of bruarjokull and Eyjabakkajokul – downice of topographic depressions from which the hills were displaced by thrusting

Surface features – fluted/drumlinized

Internal structure – glacitectonized outwash or lake sediments, tops of which modified into glacitectonite

Ice-moulded hills – over-ridden thrust block moraines

Thrust block moraines 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-squeezed ridge

Bruarjokull & eyjabakkajokul, Iceland

Trapridge glacier & donjek Glacier – Yukon Territory & from Svalbard

Tectonics experienced during surge – glacier is highly fractured and 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 downflow sides interpreted as ploughs/incipent flutes produced by boulders embedded in glacier ice
- Elongation of the flutes suggest, formed during a single flow event when the basal water pressures & degree of ice-bed coupling remained shorter & much less uniform in Section
- Flutings & crevasse squeezed ridges – aspect of subglacial geomorphology of surging glaciers

Thrusting & squeezing

Zone of thrusting in the snout, lifted from the bed, thrusting in surging glaciers, supraglacial sediment

Low-relief hummocky moraine comprising interbedded sediment gravity flows & crudely bedded stratified 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 into englacial and supraglacial position

Successive surges – over-riding, overthrusting, incorporation 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 ridge

Kettle & kames topography

Differentiated from over-ridden thrust block moraine by extensive evidence of on-going meltout of buried ice

Ice cored outwash & glacilacustrine sediments

Variagated glacier surge – outbursts of supraglacial water

Landsystem model for surging glacier

Based on combination of observations from contemporary surging glacier margin & published literature

Geomorphic & sedimentological signature of glacier

Geomorphology – 3 overlapping zones

· Outer zone : of thrust block & push moraines weakly consolidated presurge sediments

Structurally – major thrust block moraine restricted to topographic depression large enough to collect sufficient sediment during the quiescent phases

· Intermediate Zone: patchy hummocky moraine located on the down-glacier sides of topographic depression, draped on ice proximal slopes of thrust block moraines & push moraines

Hummocky moraines – intensely glacitectonized fine grained stratified sediments & diamictions or poorly sorted gravels – products of thrusting, squeezing & bulldozing

· Inner Zone – subglacial deformation tills & low amplified flutings produced by sub-hole deformation during the surge

Crevasse-squeezed ridges, documenting the filling of basal crevasses, concertina eskers

Palimsets & outer surges (overridden moraines)

Proglacial outwash fans & streams (ice-cored collapsed outwash)

Ponded topographic depression on the foreland (collapsed lake

Plains)

GEOMORPHOLOGY ZONATION MAP OF EYJABAKKAJOKULL, ICELAND


CONCERTINA ESKER


CREVASE SQUEEZE RIDGE