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Lecture

Glaciers, The Ice Age & Paleovegetation pkg. Lectures from March 17th and 22nd, Including the three broad topics in the title and all their subdivisions.


Department
Geography
Course Code
GGR100H1
Professor
Sarah Finkelstein

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Glacial Processes and the Quaternary Ice Age//Chp. 17th
Glacial Processes
Agents of Erosion: Wind/water/ice act to transport materials that’ve been loosened
by physical/chemical weathering and mass wasting.
Ice: PWRful AoErosion b/c can move massive amnts. of sediment
-Ice axn restricted to glacial periods
-Glacial vs. Interglacial Periods
> Glacial: significant area of Earth covered in ice; much glacial erosion potential
> Interglacial: we’re in one. Ice sheets have retreated north to
Greenland/mountains/Arctic , but ice is still available in high latitudes/elevations
What is a glacier?
-Large mass of flowing land ice; plastic body that flows.
-Ice on land under pressure begins to flow, becoming a glacier
-Mass balance: glacier fed (accumulates) from precipitation in form of snow at the
top, and ablates (melts) at the bottom.
> Can’t form in dry, high temperature areas.
>Glaciers form in conditions of low temperature AND adequate snowfall/ppt.
>Firn: Beginning of a glacier.
> In certain areas, snowfall from winter doesn’t melt in summer and continues to
accumulate. Persisting snow is compacted over time into glacial ice (firn), due to
intense pressure from the heaviness of piling precipitation.
How do glaciers move?
- Under pressure, ice loses its rigidity. Because of this pressure it becomes plastic,
able to flow, and moves downslope like water (distinguished from normal brittle ice
as we know it). Can flow downslope over landscapes without breaking. Will flow
downslope direction despite accumulation or ablation.
-Severe erosion: Glaciers can be 1000s of metres in height; weight transports huge
amnts of entrained material as it flows, plucking material from ground downslope to
the lowlands
Mass Balance
-determines whether a glacier is growing or shrinking
-If there’s more ablation than accumulation, there is a retreat of the terminus
(end/bottom of slope).
Equilibrium States
-Glacier is in equilibrium when ablation = accumulation (flow is continual however)
>Changes in ablation/accumulation rate correspond to glacier advance/retreat and
a new equilibrium
x Glacial retreat, Quelcccaya Ice Cap in Peru (5400 m above sea LVL): procession of
glacier up the valley in proglacial lake
>Proglacial lake: contains meltwater off the glacier, gated by sedimentary border
left over from glacier’s movement

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Glacial Processes and the Quaternary Ice Age//Chp. 17th
Alpine glaciers
– rivers of ice that begin formation up in mountains then flow downslope,
excavating…
> …distinctive U-shaped valleys
-3 stages of glacier-created landforms:
1). mass wasting: basic rivers flowing down mountainsides, v-shaped valleys formed
in mountainsides.
2). glaciations: environment changes and glaciers begin forming during glacials.
>Erosional landforms of Glacials:
cirques: are bowl shaped depressions of heads of valleys, representing where
glaciers are formed, and where they first start excavating those mountainside
valleys
arêtes: when cirques form adjacent to each other in different orientations
horns: when at least 3 cirques form on diff. faces of mountain
>Depositional landforms of Glacials
x will only form in lowlands, not in uplands b/c of steep slopes and mass-wasting
moraines: endpts. of glacier movement, after it has crushed a lot of sediment on its
way down a slope and deposits crushed material at its base (terminus), as ablation
sets in
3). ice recession: main glacial trough is much steeper than the tributaries, creating
‘hanging valleys’ where waterfall forms b/c of steepness.
>Features resulting from ice recession:
tarn: mountain lake that forms during ice recession
Paternoster lakes: series of cirques with tarns inside that form next to each other in
the shape of rosary beads
fjords: U-shaped valleys carved out by glaciers, then flooded by ocean after glaciers
recede. Their formation is tied to sea LVL.
Ice sheets
- If temperatures stay cold enough in summer, ice accumulates when in flows into
lower elevations/latitudes (lowlands), and become coalitions of ice sheets that can
blanket entire landscapes. This happened during Pleistocene in Canada.
-Only ice sheets in the Antarctic (~14 mill. km2) but also in Greenland (~1.7mill.
km2) exist today, and they cover entire continent(s) besides their coasts
> Because we’re in an interglacial, no glaciers in lowlands, but yes glaciers in
Antarctic/Greenland
March 22nd lecture starts at Continental glaciers
Continental glaciers: The importance of depositional landforms
-Entrainment (plucking, abrasion…) transport and deposition of eroded material in
lowlands from uplands
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