Glaciers

Demonstrated in late 1800’s that glaciers could move. Put stakes across glacier,
checked in four year increments, stakes were moving downhill. Therefore, the glacier is
moving downhill. Rate of movement wasn’t the same, moving faster in middle than on
edges.
Top of glacier – brittle zone, behaves as solid block of ice, can fracture. Inside glacier,
ice is flowing very viscously like a plastic. Amount of internal deformation and rate of
movement is slower at bottom of glacier, but still happens. Called “Basal Slip”. Bottom
of glacier melts a little bit due to friction, more melt water might help glacier slip faster.
Glacial budget – Rate of accumulation near top of glacier versus rate of glacial melting
near bottom.
Zone of Accumulation — Snowline (firn limit, boundary between two zones) — Zone of
Ablation (Wastage)
If amount of accumulation is equal to amount of ablation, glacier will stay the same size.
If amount of accumulation is greater, glacier will advance downhill
If amount of ablation is greater, glacier will retreat.
Glacial Erosion
Thickness of ice is correlated to depth to which glacier can erode. Thicker glacier can
erode deeper.
Cirques: Top of glacial valley
Arete – Ridge between two different glaciers
Horn – Mountaintop between two glaciers.
Glacial meltwater leaves behind a lake – Tarn
If several tarns are strung together, called pater noster lakes
Glaciers transport sediment and erode very effectively.
Rockfall – rocks fall onto glacier from free/thaw cycle
Plucking – glacier picks up sediment from glacial valley.
Glacial till – sediment deposited by a glacier. One big characteristic is that till is very
poorly sorted, angular.
Till can be deposited multiple ways.
Piles of glacial till on sides of glacier – example of Lateral Moraines.
Piles of glacial till in middle of glacier – example of Medial Moraines. Can happen from
tributary glaciers.
3rd type of moraine: Terminal Moraine: Deposited at end or “terminus” of the glacier.
Terminal moraines form in part because the ice is bulldozing sediment in front of it. As
the glacial ice melts, it leaves behind all of the stuff it is carrying.
Terminal moraines can dam up the lakes at terminus of glacier.
Crevasses – cracks in brittle zone (top) of glacier due to tension
Glacier water might be milky due to “rock flour”, really really fine sediment.
Glaciers don’t discriminate.
Louis Agassiz (1807-1873)
Swiss-American naturalist
Proposed Ice Age Theory in 1837
Found evidence for 4 different glacial periods in both Europe and America
Dividing glaciers into two different types:
1. Mountain glaciers (aka Valley, Alpine), restricted to valleys, flow downhill
2. Continental glaciers (move outward in all directions from thick part in the middle)
Evidence for bigger mountain glaciers and evidence for continental ice sheets.
Number of protons always tells you which element.
Different numbers of neutrons & different masses makes up each isotope.
Benthic Foraminifera – sediment made up of skeletons in ocean, have a record of ocean
water through time. Analyze ratio, see if it was heavier or lighter over time.
What we use to figure out how climate has been different, context we use to see if
glaciers are related or not.