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Lecture 33

GEOG 1400 Lecture Notes - Lecture 33: Basal Sliding, Laurentide Ice Sheet, Franz Josef GlacierPremium

4 pages61 viewsFall 2015

Course Code
GEOG 1400
Andre Robert

of 4
Geog 1400 – Jan. 7th
Stratification/Water Movement Within Lakes (Last class)
- Different layers, top is warmer, bottom is colder. Highest density at the bottom, lower at
the top.
- Epilimnion: Top Layer of warm water.
- Hypolumnion: High density
- Thermocline: Temperature changes more rapidly in between the top and bottom layer.
- In winter everything switches. So the warm part is at the bottom, cool part at the top.
- The wind will trigger mixing of the lake, strong mixing and the top will get colder.
- This tends to be more specific in larger lakes.
- Alpine glacier, google image. At the bottom is the valley and lots of debris. Downslope,
valley glacier.
- Rivers and glaciers the two most significant.
8. Glacier formation and movement
- Today just about formation and movement.
a) Glaciers – Intro
- Three categories:
Past continental ice sheets.
Current major ice sheets.
Valley glaciers.
- Over the geological time there have been many glaciations. About 15000 years ago there
was a huge glacier covering a big part of North America and Europe.
- If you are in a zone that was once glaciated there are usually a lot of debris, and things
that was created during that time.
- That ice sheet was referred to as the Laurentide Ice Sheet.
- This was the last glaciation.
Maximum Glaciations North America
- Area covered by the Laurentide ice sheet.
- Plastic because the glaciation deforms, moves and changes shape.
Ice Growth
- How does this work?
- Accumulation of snow happens, you have compaction of the snow layers, the
consequence is that there is change in density, light or heavy. The density of the snow
varies between temperatures and distance, etc.
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- As you have accumulation, physical compaction takes place, takes away the air bubbles,
and there is a gradual increase in density.
- Transition stage between snow and ice, related to compaction of the snow and the
- As the process of this continues you get a glacier.
- Change in density is the main part of the definition.
Transformation – Snow to Ice
- If you have cold temperatures but low snow accumulations, it will take longer, same with
dry places that are very cold.
- Snow accumulation rates and time is important.
c) Alpine Glaciers
-This diagram of the glacier is important, the terms will be defined in this lecture and the
next lecture.
- Movement due to gravitational flow and sliding of the bedrock. Internal flow is always
Athabasca Glacier (Rockies, AB)
- Comes from the Colombia ice fields which sits on top the of the rockies.
- From that ice field there are valley glaciers flowing down.
Saskatchewan Glacier
Franz Josef Glacier, NZ
- Valley glacier.
- South island of New Zealand.
- Even more spectacular.
- Bottom is a few meters above sea level and not very cold.
- A lot of precipitation, and it is a dynamic system.
Alpine Glaciers
- Valley glaciers originate from a depression in the bedrock where snow accumulates, and
when it reaches a certain point it flows out off the cirque and the formation of the entire
ice mass begins. (zone where is feeds the glacier – accumulation zone)
- Once large enough it flows slowly from the upslope (zone of accumulation) to downslope
(the zone of ablation)
Glacier Cirque
- Mountain with a glacier.
d) Glacier Mass Budget
- One of the best indicator of the impact of gradual warming conditions. Of climate change.
Shrinking in size, usually the front moves up the valley.
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- Input is snow precipitation.
- Output: Melting, calving (when the front of the ice mass goes into the sea or lake, ice is being
lost through calving), evaporation.
Glacier Mass Balance
- If input is bigger than output, it means the glacier will become thicker and longer as well.
If there is an increase in size, there is a forward movement.
- If it is reverse, the glacier would be shrinking. When it is shrinking the front is retreating
going up valley and gradually becomes thinner.
Mass Balance
- The whole ice mass is what we observe. Athabasca glacier, is moving fast.
- Upper section, high elevation, zone of net? accumulation of ice and snow.
- Down valley, is net loss due to the zone of melting.
- Movement of ice from the up to down.
- If it is the same from up and down, the ice mass will remain the same.
- The net shrinking if the top has more than the down.
- If there is more ablation than accumulation, the ice mass will shrink and the glacier will
Glacier Retreat
- Due to climate change.
- Many glaciers at the moment are in a state of retreat.
Dynamic Balance
- No real movement of the front,
- Ice Mass remains the same
- Accumulation and ablation rates are more equal.
Tidal Glacier (Calving) – Alaska.
e) Ice Movement
- Huge ice mass which moves slowly.
- Given the size there are two types of ice movement mechanisms.
- Slow movement could be a few meters over 10s of years?
- To see the movement they set up poles at the bottom of the glacier.
Glacier Ice Movement
- At the top you have a zone where the ice is brittle. At the top it is fast movement. Creates
cravisis due to fast movements. Hundreds of meters of ice creates huge pressures which
causes the downslope.
- Friction asserted by the valley walls.
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