IMPORTANCE OF THE CRYOSPHERE
The cryosphere is part of the hydrosphere and includes glaciers and frozen sea ice. It
is located mostly at the north and south poles.
The cryosphere is an effective agent of erosion and deposition. It can significantly
modify landscapes.
The cryosphere impacts Earth’s climate by cooling water and air, and setting up
oceanic and atmospheric circulation patterns.
The cryosphere impacts the biosphere because water cooled by polar ice has the
largest concentration of dissolved oxygen and supports a diverse fauna (oxygen gas is
most soluble in cold water).
WHAT IS A GLACIER?
Glacier- A large, long-lasting mass of ice that forms on land and moves downhill
under its own weight.
The two general categories of glaciers:
1. Alpine/Valley Glaciers
2. Continental/Ice Sheet Glaciers
ALPINE/VALLEY GLACIERS
They are formed in mountainous regions of high elevation (Example: Glacier National
Park in Montana).
They are confined to a valley and flow downhill due to gravity.
CONTINENTAL/ICE SHEET GLACIERS
These are glaciers that exist over a large part of a continent (> 50,000 km2) in
regions near the earth’s north or south poles (Examples: Antarctica, Greenland).
Antarctica has 85% of glacier ice currently on earth, and Greenland has 10%.
If Antarctica’s ice were to melt, the sea level would rise 70 m or 230 ft.
In Antarctica, two ice sheets (west and east) flow downward and outward from a
central point: the Transantarctic Mountains. The East Antarctic Ice Sheet = 2700 m
thick and the West Antarctic Ice Sheet = 4800 m thick.
A SHORT VIDEO ABOUT GLACIERS IN YOSEMITE
NATIONAL PARK.
http://www.youtube.com/watch?v=mgnzSTY5zRg&list=PL0ABC36F79629E0F9
&index=3
FORMATION AND GROWTH OF GLACIERS
Transition from snow to glacier ice: Powdery snow → Granules → Firn
(somewhat compacted)→ Glacier ice
FORMATION AND GROWTH OF GLACIERS
Glacier ice moves downhill and is eventually lost (ablated) by melting,
evaporation, or calving of icebergs.
FORMATION AND GROWTH OF GLACIERS
Zone of accumulation - The upper part of a glacier where snowfall is collected.
Zone of ablation - The lower part of a glacier where ice is lost.
Equilibrium line - The boundary between these zones. It marks the highest point at
which the glaciers snow cover is lost during the warm season.
The equilibrium line may migrate from year to year depending upon where there has
been more accumulation or more ablation.
If there is more accumulation than ablation→ the equilibrium line moves down the
glacier (positive budget).
If there is more ablation than accumulation→ the equilibrium line moves up the
glacier (negative budget).
Terminus - The lower edge of a glacier (the position depends on the glacier’s budget).
The velocity of ice movement varies across the glacier with velocities being highest in
the thick center and lowest at the thin edges (due to drag).
MOVEMENT OF ALPINE GLACIERS
Glacier speed varies from millimeters to tens of meters per day (depends on slope).
The base of a glacier slides over underlying rock on a thin layer of meltwater (basal
sliding).
The thicker parts of glaciers (the centers) move faster than thinner parts of glaciers
(the edges) which experience more frictional drag.
The lower part of glaciers flows plastically as individual ice grains move relative to
each other (the zone of plastic flow). Here the ice grains deform to accommodate
movement.
The upper part of the glacier moves rigidly. Here fractures called crevasses may
develop here.
EROSION BY GLACIERS
Meltwater at the base of a glacier may work its way into cracks and freeze. Pieces of
bedrock may be worked loose and picked up by the moving glacier in a process is called
plucking.
Rocks carried along at the base of the glacier may grind and polish the bedrock
(abrasion). Large rocks may produce glacial striations in the bedrock as they move
over it.
EROSIONAL FEATURES OF ALPINE GLACIATION
(ANGULAR TOPOGRAPHY)
EROSIONAL FEATURES OF ALPINE GLACIATION
(ANGULAR TOPOGRAPHY)
1. U-Shaped Valley: The characteristic cross section profile of a valley carved by
glacial erosion.
EROSIONAL FEATURES OF ALPINE GLACIATION
(ANGULAR TOPOGRAPHY)
2. Hanging Valley: A small valley that terminates abruptly high
above a main valley
EROSIONAL FEATURES OF ALPINE GLACIATION
(ANGULAR TOPOGRAPHY)
3. Truncated spur – The triangular facet produced where the lower end of a ridge has
been eroded by glacial ice.
4. Rock-basin lake – A lake occupying a depression caused by glacial erosion of bedrock.
5. Cirque – A steep-sided, amphitheater-like hollow carved into a mountain at the head
of a glacial valley.
6. Horn – A sharp peak formed where cirques cut back into a mountain on several sides.
7. Arètes – A sharp ridge that separates adjacent glacial valleys.
EROSIONAL FEATURES OF CONTINENTAL
GLACIATION (ROUNDED TOPOGRAPHY):
The weight of the moving ice sheet produces rounded knobs and striated bedrock. The
orientation of the striations can be used to interpret the direction of movement of the ice
sheet.
Thick ice sheets may bury mountain ranges, rounding and streamlining them in the
direction of ice movement.
DEPOSITION BY GLACIERS
Glaciers pick up rock fragments from the underlying bedrock and from the valley walls.
Glaciers carry the debris without tumbling or sorting. The deposited debris is called
glacial till (angular, poorly sorted, and unlayered). When till becomes lithified, it is
called tillite.
Large boulders transported large distances by glaciers are called erratics.
DEPOSITION BY GLACIERS
Moraine: An elongate deposit of glacial till.
FIVE TYPES OF MORAINES
1. Lateral moraine - Forms along the sides of a valley glacier as rocks fall from the steep
cliffs of glacial valleys.
2. Medial moraine - Form where two tributary glaciers come together and adjacent
lateral moraines join.
3. Recessional moraine - Deposits produced as glaciers recede during melting.
4. End moraine - A type of recessional moraine that forms at the terminus of a glacier
during glacial recession as debris piles up long the front of the ice. They tend to be
crescent shaped.
5. Terminal moraine - Special type of end moraine that marks the farthest extent of the
glacier.
LATERAL MORAINE
DEPOSITION BY GLACIERS
Drumlin- A streamlined hill of till produced by continental glaciers (the origin is not
entirely understood). Drumlins point in the direction of ice movement.
DEPOSITION BY GLACIERS
Outwash Deposits- When glaciers melt, braided streams develop on the surface of land and
carry away material known as outwash.
Eskers- Under the ice, meltwater moves in tunnels and carries sediments that can be
deposited in sinuous ridges of sediment called eskers (well-sorted and cross-bedded).
DEPOSITION BY GLACIERS
Kettle - A small depression in outwash formed when a block of glacial ice gets buried
by sediment. When the ice melts, a depression remain. These may fill with water
creating small lakes (glaciated Minnesota is the land of 10,000 lakes).
A kettle in a braided depost of Alaska's Bering
Glacier
DEPOSITION BY GLACIERS
Varves- Seasonal deposits of silt and clay that form alternating light and dark layers.
Each silt-clay set represents one year:
-The silt is deposited during the warmer part of the year when more melting and
sediment transport occurs.
-The clay is deposited during the colder part of the year when the lake is frozen and
the clay can settle out of suspension.
Varves can be used to determine how long a glacial lake lasted.
GLACIATION IN THE PAST
At times in the past, colder climates resulted in more extensive glaciation than the
present.
The last glacial period began ~2,000,000 years ago and ended ~10,000 years ago.
The North American ice sheet extended as far south as Ohio and Illinois.
Outwash till was deposited over the Midwestern U.S., providing good soil for farming.
The Great Lakes occupy basins that were formed by heavy lobes of ice. These basins are
undergoing isostatic crustal rebound.
Sea Level was ~ 130 m lower than it currently is today because sea water was locked up
in large ice sheets at the poles. Submerged stream channels and land mammal fossils on
the continental shelf support lower sea level.
During the end of last glaciation, the climate was more humid than today. In the western
US, there was significant rainfall and numerous lakes (called pluvial lakes) once existed in
Nevada, Utah, and California (Example: Utah's Great Salt Lake).
GLACIERS IN NORTH CAROLINA?
In 1973, two Appalachian State University geologists claimed to have discovered proof
that the Appalachian Mountains in North Carolina had U-shaped valleys that were
formed by glaciers. They noted certain shapes that were found in rock formations as
proof. Other geologists have stated that they don’t believe glaciers came any further
south than Pennsylvania or Northern Virginia.
What do YOU think?