Transcript GLACIATION - School District 67 Okanagan Skaha

GLACIATION
How Glaciers are Formed
• Formed in areas always covered in snow
• The lowest level that permanent snow
reaches in the summer is the snow line
• Freshly fallen snow becomes compressed
and crystallizes into rough, granular ice
called firn (or neve)
• Lower layers of firn become solid ice due
to compression, and the ice begins to flow
downward or outward
Zones of a Glacier
Valley (Alpine) Glaciers
• Long, slow-moving, wedge-shaped
streams of ice
• Occur in areas where mountains stretch
above the snow line
• Sharpen mountain peaks by grinding away
at their sides
Alpine Glacier
Continental Glaciers
• A moving mass of ice (ice sheet) far larger
than an alpine glacier
• Found in polar areas where the snow line
is close to sea level and there are wide
areas
• Circular or oval in shape
• Covers most mountain tops so it grinds
down peaks and leaves them polished and
rounded
Glacial Movement
• Weight of ice and snow push on low
layers, and cause layers to melt and
refreeze (moves downhill)
• Glaciers move more rapidly at the surface
vs. the base, and faster in centre vs. sides
• When a valley glacier comes to a great
slope, fissures (crevasses) form across
the glacier
• The end of the glacier is the ice front
Glacial Till
• Glaciers move loose rock from valleys (like
rivers) but they can carry much larger particles
(giant boulders for example)
• When particles are deposited, they form
moraines (lateral, medial, end or terminal
moraines, depending on where they occur)
• Rock flour is fine sand and silt formed from the
crushing of rock under a glacier
• Melt water can be a milky white colour as a
result and is called glacial milk
The Marks of a Glacier
• Striations: long parallel scratches left by
rock material (they show glacier direction)
• Cirque: a semi-circular basin at the head
of the glacial valley
• Aretes/Horns: formed where two or more
cirques cut into the same peak
• Glacial trough: a u-shaped valley formed
when a glacier scours the valley floor and
makes the walls more vertical
The Marks of a Glacier
• Tributary glaciers are smaller and have
less erosional power, so they form smaller
valleys which are higher than the main
glacier, and form hanging troughs and
waterfalls
• Lakes can be formed in basins or
depressions. Tarns are formed in cirques,
kettle lakes are formed in kettles.
Glacial Deposits
• Drift is the name given to all glacial
deposits
• Glacial till is unsorted and unstratified
(moraines are unsorted)
• Outwash is sorted and stratified (like
stream deposits)
• Erratics are large glacial boulders
transported into an area (different from
local bedrock)
Other Depositional Features
• Drumlins: long, smooth canoe shaped
hills made of till, which point in the
direction of glacier movement
• Outwash plains: broad flat areas where
glacial meltwater pours out
• Eskers: meltwater that falls through ice
crevasses and run in tunnels under the
glacier, leaving long winding ridges
Other Depositional Features
• Kames: small, cone-shaped hills of
stratified sand/gravel formed when
streams on top of the glacier deposit their
sediments (and eventually lower)
• Kettles: large blocks of ice are buried,
then melt, leaving circular hollows
• Deltas: when glacial streams empty into
lakes or beyond the ice front