Transcript Evidence Left Behind - Learn with Mrs. Schulz

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In some places it is too cold for all the snow to melt
- This snow begins to pile up
- The weight of all the snow piling up causes the
crystals to reform into something that looks like sugar
- With more pressure these crystals begin to form
together and the air spaces between them get smaller
until there is a thick ice layer
- The glacier is now formed and will now begin to
“grow”
- Due to the forces of gravity and the presence of
water under the glacier or silt the glacier will start to
move down and out!
Fresh Snow
Old Snow
Granular Snow
P
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S
S
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Water from glacier melting then refreezing
Reduced air space
Glacial Ice
So what’s an ice cap then?
No it’s not a delicious caffeinated
drink from Tim Hortons!
It’s a glacier that forms on a large
area of relatively flat land and flows
outward from its center.
Ok, well then what’s an icefield?
It is an upland area of ice that feeds
two or more glaciers.
Valley Glaciers – form in a mountain range
as the temperature rarely allows the snow
to melt during the summer.
Ex) Athabasca Glacier
Continental Glaciers – huge mass of ice
and snow that usually occurs near the
North and South poles. They are so thick
that they cover most of the mountain
ranges below them
Ex) Antarctica and Greenland
An icefall occurs
when a glacier flows
over a cliff.
It does not simply
break off because
glaciers are not
entirely liquid or
solid!
As the glaciers are
moving and stretching
they may stretch too
much causing a crack
or crevasse.
How is it different than
crevice?
-Glaciers will either be advancing or retreating.
-Advancing – the front edge of the glacier is moving further down
the hill.
-Retreating – the front edge of the glacier appears to be moving
up the hill.
-Despite this, the glacier is ALWAYS moving downhill.
-This happens when the rate of melting of the edge of the glacier
is greater that the rate the glacier is advancing.
-THIS means the glacier is retreating, the glacier is not actually
moving back up the hill it’s just melting rapidly!
-Pack ice – sheet of ice rarely more than 5
m thick that forms on the ocean that easily
breaks off.
- With that said icebergs DO NOT come
from pack ice!
- Icebergs – large chunks of ice that
originate from continental glaciers.
- Chunks of ice calve, break off, from the
glaciers as they move into the ocean
- Did you know that glaciers are huge under
the water compared to what you see? Why
do you think this is??
Even after glaciers are gone there is much evidence that they were once
present!
Glacial Erosion
-Glaciers are amazing eroders! They bulldoze, break up, and scrape the
underlying rock sediment.
Evidence Left Behind
-Striations – marks left by the rocks in the bottom of the glacier in the
underlying rock
- Cirques – bowl-shaped basins caused by erosion
- Arête – caused by two cirques on either side causing a ridge.
- Horn - - caused by three or more cirques causing a sharp peak.
-U-Shaped Valley – caused by glaciers because they grab rocks from the
side and the bottom as opposed to rivers.
- Moraine – a large ridge sediment left as a result of the
glaciers bulldozing action.
- Till – the mixture of different sized sediments dropped
from the glaciers base as it has melted
- Outwash – material deposited by the water of a melting
glacier.
- Erratics – huge rock fragments picked up from one
location and dropped at another by advancing and
retreating glaciers.
- Esker – a ridge of sand and gravel left by a river of melt
water within the glacier.
- Water from the glacier melting flows down the
glacier.
- It can be seen as rivers or streams on top of the
glacier but usually eventually plunge deep into the
glacier via millwells.
- A millwell is carved by the streams as they move
down through the glacier. They can be 30 stories
deep!
- These millwells lead to a network of streams
below the glacier which eventually emerge from the
toe of the glacier.
- Glaciers act as incredible stores of freshwater.
They slow down the water cycle and hold the water
for when it is needed most, the summer
- They also provide a vast amount of information
about the Earth’s past climates because of the way
they accumulate ice.
-Despite what you may think there have been at least 7
major ice ages in the past several million years!
- The last one covered almost ALL of Canada!
- How do we know this?? (Think about what we were
JUST talking about)
- There are many hypothesis as to how an ice age
starts: reductions in the Sun’s radiation, increase in
volcanic activity, mountain formation, tectonic plate
movement changing currents, or changes in Earth’s tilt.
Review:
1) What is the difference between an ice cap and an
icefield?
2) List as many evidence for glacial activity as you can.
3) Why are glaciers crucial for life on Earth?