Glaciology and
Glacial Processes
Geography 1000B
Rivers of Ice
Types of Glaciers
Alpine Glaciers
valley glaciers
piedmont glaciers
tidal glacier
Continental Glaciers
largest
ice sheets
ice caps
smallest
ice fields
Glacier Mass Balance
South Cascade Glacier Mass Balance
Glacial Movement
and Crevasses
Open crevasses
form in extensive flow,
with thrust faulting in
compressive flow
Glacial erosion, transportation
and deposition
The power of a glacier to move
material is a function of its
thickness and its speed
The rate of erosion is greatest near
the margins of glaciers, and
is greater in temperate glaciers
than in polar glaciers.
Cold-based glaciers, however,
often have longer lifespans
Erosive Processes
1. Abrasion
Glacier ice cannot abrade
most rock due to softness
(even cold glaciers).
Rock fragments act as
abrasive elements
Ice is simply a power source
and the matrix within which
rock abrades
Source of rocks:
free rocks
subglacial freeze-thaw
quarrying
valley walls
2. Plucking
A. Glacier frozen to bed
where PMP below surface
B. Frozen bed may expand
(eg. due to thinning)
C. Glacier advances,
plucking some of the
substrate frozen to the ice
D. After several cycles
3. Quarrying and Bulldozing
Glaciers exert compressive forces
on obstructing rock and tensile forces behind
when parts of the glacier freeze to the bottom
Fractured segments of rock can be removed
Loose or fractured substrate is bulldozed
Thrust-faulting can move basal material to the surface
Repeated advancing and retreating or changes in applied force
load and unload the substrate, causing bending and fracturing.
This is exacerbated by freeze-thaw weathering.
Pressure melting point varies
with snow accumulation, surface
melting and crevassing
(freeze-thaw zones change).
If glacier is frozen to surface and
rock is fractured, it may be
plucked by the glacier above
and incorporated into the ice.
Supraglacial, englacial and
subglacial clasts are carried
by glaciers
Glacial Transportation
Types of Glacial Drift
Supraglacial Drift
Subglacial (Basal) Drift
Englacial Drift
Sediment added to a glacier by
(a)
(b)
(c)
plucking and abrasion of the substrate
falling from side or head walls of valleys and nunataks
wind transportation of material onto glacier surface
4. Subglacial Meltwater Erosion
Large amount of water generated
at base of temperate glaciers
Meltwater may flow through
fractures, tunnels and thin sheets.
Subglacial lakes form under thick
polar glaciers (sudden release
generates powerful subglacial
floods called jökulhlaups – also
caused by volcanic eruptions
beneath mountain glaciers)
Water flows also abrade the
substrate (moving sediment),
or by dissolving carbonates.
carbonates.
Salmon River jökulhlaup
Retreating Alpine Glacier
Alpine Glacial Landscape
Postglacial Landscape
Alpine Erosional Features
Norwegian Fjord
Alpine Depositional Features
Alpine Depositional Features
lateral moraine
A Valley Train Deposit
Confined, alpine version of “outwash plain”
Ice sheets: most sediment load from the surface
Alpine valley glaciers:
sediment from both the bed and side
Sediments are transported
(a)
above the glacier (supraglacial drift)
(b)
within the glacier (englacial drift)
(c)
at the base (subglacial or basal drift)
Particles tend to concentrate in patches called moraines
Lateral moraines:
Medial moraines:
Basal moraines:
Internal moraines:
derived from the valley walls
joining of lateral moraines
from the material eroded at the base
where sediments fall into crevasses,
where basal drift is thrust upward at the
terminus (thrust-faulting)
Vatnajökull
Ice Cap
Patagonian
Ice Field
Continental
Glaciers
Ice sheet
South Pole Station
Striae
Scratches produced by abrasion
Preserved best in fine-grained, brittle rock (limestone, quartzite)
Form parallel to
flow direction as
rocks within the ice
matrix abrade the
underlying substrate
The form of striae
provide a clue to
the size,
concentration and
hardness of clasts
Glacial Polish
Simple striae:
Scratches of various length
Wedge-shaped
and nailhead striae:
Clasts abrade bedrock progressively
deeply until they retracted back into
the ice (triangular or ellipsoidal)
Rat tail striae:
Ridges formed downstream from an
obstruction due to abrasion
Polished surfaces
or fine scratches:
Moving mass of silt or sand finely
abrades underlying substrate
Rat-tail
Crescentic
gouges
Semilunate scours
formed when rock
fragments removed
between fractures
Often concave upstream
due to pressure distribution
Grooves
Linear erosional features
formed in solid bedrock
Less than 2m deep
About 50-100 m long.
Striae visible inside
Formation mechanism:
Large boulders or bands
of debris gouge the substrate
further abrasion by sediments
in ice or subglacial water
Sperry Glacier, Montana
Potholes
Potholes:
Round (often deep) bedrock scours formed when
small cavities are enlarged and deepened by rock
clasts caught in turbulent vortices. The original
clast is often still in the (now dry) pothole.
Large-scale Erosional Features
Formed by glacial plucking, often accompanied by abrasion
and flowing water.
Roche moutonnée
Streamlined forms with a
smooth, gentle upslope
portion and a steep,
jagged downslope portion.
Formed by both ice sheets
and valley glaciers
Roche moutonnée
Formation of Roche Moutonnée
1. Pre-existing morphological irregularity of some sort
(eg. small outcrop of relatively hard rock – often igneous or
metamorphic)
2. High stresses form upstream causing basal melting and the
glacier slides
3. Embedded clasts abrade the bedrock upslope
4. Downslope, there is a pressure drop. The glacier freezes
to the base.
5. As glacier pulls away, tension causes quarrying or plucking of
fragmented rocks downslope.
Roche moutonnée, Yosemite National Park
Alpine roche
moutonnée
Steilimmigletscher,
Bernese Alps,
Switzerland
Cragg and tail
Crag and tail,
Princess Mary Lake,
Nunavut
Resistant bedrock knob
Streamlined remnant of
bedrock or sediments
on the tail (lee side).
Castle Rock and Edinburgh Castle, Scotland
Castle on cragg; Royal Mile on tail
Flutes
Sub-parallel grooves
Ridges of variable size
Form in flat areas,
parallel to the direction
of glacier movement
Form on bedrock or
sediment-covered terrain.
Mostly erosional, but also
depositional as basal
sediment is squeezed into
fractures at the base of
the glacier.
Fluted terrain, Peterborough, Ontario
Drumlin
Drumlin Composition:
Composed of till, sometimes
stratified
Drumlin Origin:
Erosional
Depositional
Meltwater
Reworking of
subglacial
sediment
Drumlin Swarm
Drumlin Shape:
Oval, streamlined, hills, shaped
like inverted spoons or tear-drops
(blunt, rounded heads and long,
pointed tails along a straight axis).
Lemniscate loop shape. Simple
or composite
Generally 1-2 km long, 400 to 600
m wide and 15 to 30 m in height
Vary in size and shape, especially
in different fields
Often occur in staggered pattern
associated with moraines, and
eskers
Continental
Glacier
Depositional
Features
Esker
A sinuous low ridge composed of sand and gravel formed by
deposition from meltwater running through a channel beneath or
within glacier ice.
Terminal Moraines
One or more subparallel ridges of accumulated glacial
drift at the front of a glacier
Similar in shape to the
glacier terminus
Formed because glacier
terminus remains stationary
while the rest of the glacier
continues to carry sediment
Often have a hummocky topography (knobs and kettles)
Kames and kettle lakes are the result of differential ice
melting and sediment release
Interlobate Moraines
Form when a large
volume of sedimentladen meltwater is
funneled between
receding glacier lobes
(eg. Oak Ridges
Moraine,Ontario)
Up to 50m high and 10
to 100’s of kilometres
long
Consist of stratified
sand and gravel