Glaciers 3

Supra- vs sub- glacial sediment sources

o   Supraglacial rockfall/freeze-thaw/pressure-release avalanches, windblown sediment, volcanic tephra, meteorites

o   Subglacial abrasion, quarrying, meltwater

o   Subglacial the most effective erosion

What is the importance of moraine deposit shape?

it can show surges in deposition

Supraglacial sediment characteristics

• clasts are angular

• few fines

• loose matrix

• poorly sorted particles

What is englacial transport?

debris/sediment folding and moving inside a glacier

Types of subglacial transport

• traction - debris along bed(drag exerted must be > frictional force keeping clast in position)

• suspension - debris moved englacially(regelation + deformation)

• deformation layer -   transport in a deforming sediment layer within the bed. Deformation of basal sediments can make up 90% of motion in some glaciers

Subglacial sediment characteristics

• low level transport

• blocky, faceted and strirated - faces created through clast on clast contact

• larger clasts + matrix of fines = diamict

Low- and high-level transport mixing

• Deformation may transfer sediment (especially at snout) through thrusting and folding

•   Occurs during compressive flow at the snout - Change from warm to cold ice at the glacier bed, Flow against reverse subglacial slope, Surging glaciers

Depositional landform categories

• morainic - sediment contact and deposited in ice

• glaciofluvial - produced by glacial activity and interacted with water

Types of depositional environs

• direct glacial sedimentation(morainic landforms and sediments

• indirect glacial sedimentation (watery environs associated with ice) - glacifluvial, glacilacustrine, glacimarine

sub- vs supraglacial sedimentation

• subglacial(active ice) - lodgement till(ground moraine and till plains), push moraines

• supraglacial(stagnant/wasting ice)- melt out(ablation moraine), re-sedimentation(flow till)

Types of moraine/till

• push moraine

• ground moraine and till plains

• ablation moraine

• flow till

Till vs moraine

o   Diamict - general term for sediment, till specific to glaciers

o   Drift - any sediment produced by any glacial processes

o   Till - a glacial diamict

o   Moraine - a geomorphic feature often composed of till or mass movement deposits

Subglacial deposition

o   Lodgement - drag<resistance to movement, often clay rich with large resistant clasts

o   Characteristics - Particles aligned closely  with direction of ice flow, dense and well consolidated, structureless, may contain shear planes

supraglacial deposition

o   Melt out - conduction and insulation

o   Resedimentation - sediments reworked by gravity and meltwater