Glacial processes: the inter-linked system of erosion, transport, and deposition

Glacial Processes Overview

Glacial processes - the inter-linked processes of the system

1. WEATHERING /
   EROSION
2. TRANSPORT
3. DEPOSITION

Weathering and Erosion Mechanisms

Weathering Types

Frost-shattering -
Weathering
· At the snout

Erosion Types

Abrasion
Plucking
Fracture or traction
Dilation
Meltwater erosion
Supra glacially
En glacially
Sub glacially

• Sublimation of
  surrounding ice
• Friction against the
  base

Distinguishing Erosion and Weathering

Distinguish between erosion and
weathering
. Weathering refers to the physical disintegration
and the chemical decomposition of rocks at that
place
· Erosion refers to the removal of soil and rock and
their transport by the agents of erosion (glaciers,
wind, sea, rivers).
. Common types of weathering in glacial
environments - handout.

Glacial Landform Development

How might these have developed? Why?
What does the marks tell us about past glacial areas?

Detailed Glacial Erosion Processes

Abrasion in Glacial Environments

1. Abrasion occurs because of entrainment. This is when
   ice includes angular frost shattered material, which
   scours the landscape. Large rocks carried below the ice
   often scratch the bedrock to from striations or
   scratches.

Plucking (Quarrying)

1. Plucking - often referred to as quarrying. This is when
   meltwater freezes part of the underlying bedrock to the
   base of the glacier. Any loose fragments are then
   plucked away as the glacier moves forward.

Weathering and Erosion Link

1. WEATHERING /
   EROSION

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Further Glacial Erosion Processes

Fracture and Traction

Glacial erosion processes
3. Fracture and Traction occur as a result pf the crushing
effect of the weight of moving ice passing over the rock and
variations in pressures lead to freezing and thawing of
meltwater (basal melting), which aids the plucking process.

Dilation

4. Dilation occurs as overlying material is moved, causing
fractures in the rock parallel to erosion surfaces as the
bedrock adjusts to the unloadng.

Fluvio-glacial Erosion

4. Fluvio-glacial erosion
Glacial ablation can produce large amounts of meltwater.
Meltwater streams inside the ice are highly erosive due to
their high velocities and because the water is under pressure
(trapped between the ice and rock) it can move uphill as well
as down.
gettyimages
Carl R. Battreall
597301608

Glacial Transportation Methods

Material Transport in Glaciers

Glacial transportation
2. TRANSPORT
· Glaciers acts like giant conveyor belts, which
transport material from mountainous areas to
adjoining lowlands. Material can be carried in three
ways:
. Supraglacial - mainly weathered material on the
top of the ice
· Englacial - formally supraglacial material, but now
buried by fresh snowfall and carried within the ice.
· Subglacial - material carried below the ice, which is
dragged and pulverised by the overlying glacier.

Glacial Landform Scales

Macro-scale Landforms

Glacial processes and the formation of glacial landforms
Macro-scale
landforms
These are large scale landforms
that have been created by a
combination of glacial processes
over time.
E.g. Ice sheet eroded landscapes,
cirques, aretes, pyramidal peaks,
terminal moraines.
Alamy/Vincent Lowe

Meso-scale Landforms

Meso-scale
landforms
These are intermediate scale
landforms that have been created
mostly by erosion but also can be
created by meltwater erosion.
E.g. Roches moutonees, drumlins,
kames, eskers, kettle holes
(meltwater (fluvial) landforms)

Micro-scale Landforms

Micro- scale
landforms
These are small scale landforms
that are in some cases quite small
in size
E.g. Striations, chatter marks and
erractics

Factors Influencing Plucking and Abrasion

Factors for Plucking and Abrasion

(1) What might influence how much plucking or abrasion happens?
Angularity of
clasts
Hardness of clasts
Quantity of
debris
Thickness of
Ice

Abrasion Definition

ABRASION
The grinding away of bedrock by
fragments of rock which may be
incorporated into the ice

Plucking Definition

PLUCKING
Highly fractured
and jointed rock
promotes dilatior
and freeze-thaw
Lithology -
amount of
jointing in
rock and
overall
hardness.
The pulling away rocks by localised
melting around an object. It is a bit
like pulling a loose tooth.
Semi-permeability of bedrock
leads to maximum meltwater
at glacier-bedrock face
Thermal regime of
the glacier
Presence of
meltwater

Glacial Movement and Erosion Example

Regelation Creep and Erosion

Example:
Movement = regelation creep
Processes = abrasion and plucking
Ice movement
low pressure/
refreezing
high pressure/
melting
water freezes
in cracks
abrasion by
rock fragments
fragments plucked
from surface
Abrasion - drags the material along the base of the glacier leaving striations

Erosional Landforms

Landforms Associated with Cirques and Valley Glaciers

Erosional Landforms
Cirque/ Corries
Valley glaciers
Ribbon Lake
Landforms
associated with
cirques and valley
glaciers
Aretes
Glacial troughs
Pyramidal Peaks
Hanging Valleys

Landforms Associated with Ice Sheet Scouring

Crag and tail
Landforms
associated with ice
sheet scouring
Knock and Lochan
Roche Moutonees
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Truncated Spurs
tkahoot
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