Glaciers 4

Importance of meltwater

o   Ice shelf break has sea level implications

o   Outburst flood hazards

o   Rapid changes to Greenland ice sheet

o   Economic values of deposits

Boundary conditions of meltwater

• Water in glacial system usually surface melt and rainfall

•   Lakes can form and disappear on glacier surface very quickly

• Water enters glacier through holes called moulins and moves through englacial channels

meltwater routing

•   Meltwater generation and routing can vary a lot daily and seasonally

Factors effecting basal meltwater routing

·       Basal thermal regime(cold/warm-base)

·       Permeabilty of bedrock

·       Volume of meltwater

supraglacial meltwater types

•   Supraglacial channels

• Supraglacial lakes

• Firn storage/flow

englacial meltwater types

• Supraglacial channels become englacial

• Exploitation of crevasses

• exploitation of other weaknesses

Subglacial meltwater

•   Efficiency of drainage systems varies significantly depending on format and connectivity

• Channels can be cut into ice or substrate(e.g rock or sediments)

• Water can flow through underlying sediment

Erosional meltwater channels

• Can be cut in front(pro-), at the side(marginal) or beneath(sub-) of the ice - Different characteristics depending on where its cut

• Subglacial channels can flow uphill due to hydraulic pressure

• Mapping channels can show the evolution of an ice body over time its basal thermal regime

Glacial depositional environments

• Sediments are sorted

• Sands, gravels and fines mostly

•   Sediments are beddedàsediment is arranged in layers which reflect changes in the environmental conditions

• Grainsize reflects energy flow

Proglacial landsystems

• Dominated by meltwater

• Sands and gravels deposited(Sandur/outwash plain, Eskers, Kames)

• Braided rivers - unstable

• Grainsize relative to proximity to snout

• Fine grain sedemints deposited in standing water(kettleholes)

What are Eskers?

• Product of glacial drainage channels formed en- or sub- glacial

• An inversion featureàridges that represent previous voids in the ice which now have glaciofluvial sediments deposited

What are Kame Terraces

• Inversion feature

• Relate to sediments once deposited in basins in ice

• Sediments are a mix of lacustrine. Deltaic, mass movement and glaciofluvial