EQ2 What processes operate within glacier systems?

The Glacier Landform System and Glacial Processes

2.6 - The glacier landform systemGlacial processes - the inter-linked processes of the system

1. WEATHERING /
   EROSION
2. DEPOSITION
3. TRANSPORT

Weathering and Erosion Types

Frost-shattering -
Weathering
· At the snout
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.

Past Glacial Areas and Landform Development

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

Glacial Erosion Processes

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 - 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.

1. WEATHERING /
EROSION
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Fracture, Traction, and Dilation in Glacial Erosion

3. Fracture and Traction occur as a result of 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.
4. Dilation occurs as overlying material is moved, causing
fractures in the rock parallel to erosion surfaces as the
bedrock adjusts to the unloading.

Fluvio-glacial Erosion and Meltwater

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 Debris Entrainment

· Entrainment is the incorporation of debris on to or
into the glacier from supraglacial and subglacial
sources.
. 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 Transportation

2. TRANSPORT
For ice sheets, most debris is transported sub glacially via the
basal layer.
For valley glaciers there is more transport by englacial and
supra glacial debris as a result of more frequent ice contact at
their lateral margins.
As pebbles (clasts) are transported they come into contact
with each other and are ground down by a process similar to
attrition in rivers.

Glacial Processes and Landform Formation

Macro-scale 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

(1) What might influence how much plucking or abrasion happens?

Angularity of
clasts
Hardness of clasts
Quantity of
debris
Thickness of
Ice

Abrasion Factors

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

Plucking Factors

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 Landscape and Landform Features

Glacial Landscape
Combination of
glaciated features
such as corries, aretes,
glacial troughs and
hanging valleys

Glacial Landform
Individual glaciated
features such as
corries, aretes, glacial
troughs and hanging
valleys

Glacial Landforms and Processes

EQ3 - landforms!
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Plenary Questions on Glacial Processes

Plenary- answer the following
questions:
. Name one physical weathering process
. Name one chemical weathering process
· State 2 erosional processes
· What does entrainment mean?
. How can we classify glacial landforms - what are
the 3 scales?
. Name 2 factors that can influence the rate of
abrasion and plucking