Earth Science
ademola
Sept30_ice_land_sea1.pptxPSC 121 Prince George's Community College
Ice
Most of earth’s fresh
water is frozen
PSC 121 Prince George's Community College
Ice: Two flavors
# 1. Sea Ice. Ice that is floating in or covers the oceans
PSC 121 Prince George's Community College
Ice: Two flavors
# 2. Ice on land: glaciers
Greenland, Antarctica, islands in the polar north, various mountain ranges
Definitions: What are glaciers?
PSC 121 Prince George's Community College
Snow that has built up and compressed into a permanent ice field.
Key feature. Glaciers flow- they move. They are “icy rivers”.
Two flavors of glaciers
Continental glaciers: mainly Greenland and Antarctica
Pressure in center of glacier causes it to spread out
Mountain/valley glaciers, also called alpine glaciers:
scattered around the world
Gravity cause alpine glaciers to move down hill (like streams)
Note: The continental US does not have continental glaciers! Only alpine glaciers
(in the Rockies and Alaska)
PSC 121 Prince George's Community College
Glaciers: how they grow and shrink: “Mass Balance”
Grow in cold weather- winter snows accumulation
Shrink in warm weather (melt in summer) ablation
(note: if glacier is at edge of sea- it could calve and
create icebergs)
If accumulation is greater than ablation glacier grows
If ablation/calving is greater than accumulation glacier shrinks
Continental glaciers are only present in ice ages
PSC 121 Prince George's Community College
We are living in an ice age because we have continental glaciers in Greenland
and Antarctica.
If earth has no continental glaciers- some call it a greenhouse phase
But… we’re living in the warm interglacial phase.
(normally we’d go back into the cold phase in 30-50 thousand years, but man
made greenhouse gases will probably prevent that)
What happens in ice ages? That we can discuss
1. Sea level changes
2. Erosion/deposition
Why are we in an ice age now? Complicated, might have to do with
arrangement of continents. To be discussed
Map of earth during peak of last ice age
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Whats different?
Current (Robinson projection)
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How much has the land area shrunk?
The classic demo/experiment
PSC 121 Prince George's Community College
Land mass: clay
Sea ice in water
Glaciers on land
Add water here
If the ice cubes melt- which will affect water level more? Left or right.
Like wise if you take water and freeze it on land (clay) what will happen to the water
level
Continental Shelves and sea level
PSC 121 Prince George's Community College
A small change in water level can expose or cover lots of land
Continental Glaciers and sea level
PSC 121 Prince George's Community College
Continental glaciers grow sea level goes down
Continental glaciers shrink (like currently) sea level goes up
Think of hydrological cycle- water can be traded between ocean and glaciers
Eastern US during the last ice age peak: two views
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No continental shelf!
Its all land
Shows where sea level was
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Eastern US 18,000 years ago: Ice stopped at NY City, central PA
Caution: this is a modern map showing where the glaciers got to.
What the Bay really looked like (there was none- just the Susquehana River)
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Sea level was so much lower and the Bay in general is very shallow 4-6 feet deep
except in the central channel
Current continental shelf
was land at that time
Norfolk Canyon
All glaciers are melting now
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The Rhone Glacier (Alps)
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Two graphs of sea level increase
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Erosion patterns: remember this?
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Glaciers make a U-shape valley
Alaska
Erosion from continental glaciers
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Mile high glaciers scraped out (i.e. eroded) basins which became the Great Lakes
Glacial moraines: where the stuff gets dumped: deposition
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Much of NY city is built on a terminal moraine
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New York City and North side of Long Island
Boulder deposited by glacier see the scratches? (abrasion)
Boulders deposited by the glaciers- see the scratches and grooves?
Arctic Sea ice and its variation
PSC 121 Prince George's Community College
Normally melts over the summer. Minimum reached in September. Then grows back in cold weather.
But recent years, melting is greater. See blue line.
(record melt was 2012)
Sea ice is disappearing
PSC 121 Prince George's Community College
Normally melts over the summer.
Minimum reached in September.
Then grows back in cold weather.
But recent years, melting is greater.
Compare white coverage this year with
1981-2010 average
Effects of melting sea ice: good and bad
PSC 121 Prince George's Community College
Does not directly affect sea level.
Ice is already in the water
2. Good: shipping can go straight from
Europe to Asia without going
around the world. Good for
global economy
3. Bad: blue ocean absorbs more sunlight
than white ice. Will worsen
global warming and sea level
rise by making Arctic hotter
A fun web site to play with (plus articles for the homework)
PSC 121 Prince George's Community College
https://www.chesapeakequarterly.net/sealevel/index.php#Maps
Conclusion- most of PG will be unaffected. But areas along Bay and Ocean will have
problems. Also downtown DC/Baltimore/Annapolis
Summary: behavior of sea ice and glaciers
PSC 121 Prince George's Community College
Vocabulary summary
Mass balance
Accumulation
Ablation
Calving
Moraine
Sea ice
Continental glacier
Alpine glacier
Ice age
Interglacial
Interaction between hydrological cycle and rock cycle. Erosion/deposition
and creation of sedimentary rock. Also affects atmosphere.
Effects of ice on landscape and earth’s features
