Rate calculation of geomorphological process change

Rates of land surface change – focus of geomorphological research.

Problems faced

- In comprehend & compare different estimates and rates of change – reported in different forms or units

- Bias in examining areas with dynamic activity

- Scale, rate at one differential scale not be extrapolated at other spatial scale.

Glaciers & ice caps

Methods used for measuring glacial erosion

Present day glacialized region

- Use of artificial marks on rock surface later scraped by advancing ice

- Installation of plates to measure abrasion loss

- Measurement of the suspended, solutional & bedrock content of glacial meltwater streams and of the area of respective glacial basin

- The use of sediment cores from lake basins of known age which are fed by glacial meltwater

Pleistocene glaciation

- Reconstructions of periglacial or interglacial land surface

- Estimates of volume of glacial drift in a given region and its comparison with the area of the source region of that drift

Retreat of Valley Glaciers and Ice Sheets

Studies in the changes of snout positions from cartographic, photogrammetric & other data

Discovering the rates at which landscape change & the causes of these changes is a key current focus in geoscientific, environmental, ecological and archaeological research. The mechanisms are intricate involving many components – a complex of positive and negative feedback mechanisms

Erosive works achieved by glaciers

Climber geologist Bonney

- doubts about power of glacial process to achieve wholesale landform modification

- amount of materials transported by glacier as ground moraine exaggerated & much of it is swept as lateral torrents

- Appreciation of landscape based on travels

Gregory

- Opposed the idea of glaciers as effective erosive agents

- Studied nature & origin of fjords

Gardener & Jones

- Estimated the rates of denudation for raikot glacier in the Punjab Himalaya

- Achived by mapping and measuring the variable distribution & thickness of surface debris & sediment concentrations within the ice

- Calculated discharge values

Geographical Location

- Important control of the rate of erosion

- Characteristics that limit the power of glacial erosion – resistant litholigies, low relief frozen beds

- Enhance the power of glacial erosion – non resistant lithologies, proximity to former fast ice streams, thawed beds

Lithology – macroscopic physical characteristics of a rock

Erosion minimal under cold based ice at the centre of the cap because shear from ice flow is limited and ice is anchored to the underlying bedrock

Applachians – an area of active glacial erosion

O18 record from the ocean cores to deduce the duration of glaciation

West coastline of Norway – another area of active glacial erosion in Pleistocene

Application of a number of geological & geomorphological techniques

Sugden

Erosion style of an ice sheet closely related to basal thermal regime of the ice

Identified five zones

Sugden’s postulate = erosional style of ice sheet = F(basal thermal regime of ice)

Glacial abrasion

Moulded rock surfaces, grooves & striations together with large volumns of rock flours in the meltwater streams

Observation in european alps near chamonix & iceland by boulton

Attached rock & metal plates to bedrock beneath the Glacier D’Argentiere & breidamerkurjokull

Glacial Deposition

Rates of Glacial Movement

Movement types – move, advance retreat, build up wash away

Average rate: 3 – 300 m/a

Step icefalls: 1000 – 2000 m/a

Movement at lower velocities: internal deformation processes (e.g. in sluggish cold based glaciers)

High velocities – component added by basal sliding

Jakobshavan Isbrae outlet glacier in Greenland –

Flows at the rate of 7000 – 12000 m/a

Surging glaciers – periodic surges

Velocities 4000 – 7000 m/a (10 – 100 times faster than previous velocity)

Relationship between ablation & accumulation – rate of glacier flow

Glaciers with high impact of snowfall & relatively warn climate

More active than that of low snowfall & low temperatures

Retreat of valley glaciers & Ice sheets

Snout position studies obtained from cartographic, photogrammetric & other data

Glaciers provided some of the first unequivocal evidence of Quartarnary climatic change for their respond very readily changes in the rates of ablation & accumulation. Glaciers & ice caps have expanded & contracted with remarkable frequency during the multiple glacial & interglacial cycles of pleistocene

SOURCE:
The changing Earth - Rates of Geomorphological Processes, Andrew Goudie

SURGING GLACIAL SYSTEM

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

1982-83 surge of variegated glacier of Alaska

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, Iceland
Trapridge Glacier & donjek Glacier – in Yukon territory & from Svalbard
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.