GLACIAL EROSION PROCESSES

A. Introduction

erosion: entrainment & subsequent transportation of sediment

rates & patterns

B. Glacial Abrasion

Abrasion rate affected by:

basal contact pressure

basal ice velocity

concentration & supply of rock fragments

removal of glacial flour

Image credit: ©Bruce Molnia, Terra Photographics. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images

Basal contact pressure

Boulton model

abrasion controlled by effective normal pressure (stress) and ice velocity

abrasion and lodgement are part of a continuum

Hallet model

abrasion controlled by rate at which ice flows towards the bed

abrasion highest where basal melting is greatest

lodgement is independent of abrasion

C. Glacial Plucking

Rock fracturing

fractures may predate glacial advance (e.g. freeze-thaw weathering)

unloading & pressure release

variations in basal ice or water pressure may enhance existing weaknesses

Rock entrainment

rock freezes-on to glacier

D. Meltwater Erosion

Effectiveness depends on:

susceptibility of material to erosion

flow velocity

degree of turbulence

sediment load

Mechanical erosion: abrasion

Chemical erosion

E. Rates & Patterns of Erosion

Estimating erosion rates

direct observations

geomorphological reconstruction

sediment volume calculations

Patterns of erosion

primarily controlled by basal thermal regime

other factors

underlying geology

flow velocity

presence of meltwater

previous glacial history

F. Summary