2. GLACIAL ICE
Glacial ice is the largest reservoir of
freshwater on Earth, supporting one third of the
world's population. Glaciers slowly deform and
flow due to stresses induced by their weight,
creating crevasses, seracs, and other
distinguishing features. They also abrade rock and
debris from their substrate to create landforms
such as cirques and moraines. Glaciers form only
on land and are distinct from the much thinner sea
ice and lake ice that form on the surface of bodies
of water.
3. Glacier- A large, long-lasting mass of ice that
forms on land and moves downhill under its
own weight.
The Aletsch Glacier, the largest glacier of the Alps,
in Switzerland
4. Gorner Glacier in
Switzerland
Ice calving from
the terminus of the Perito
Moreno Glacier, in
western Patagonia,Argentina
The Quelccaya Ice Cap, is the
largest glaciated area in
the tropics, in Peru
7. Glaciers form where the accumulation of snow and
ice exceeds ablation. The area in which a glacier forms is
called a névé - a typically bowl-shaped geological feature
(such as a depression between mountains enclosed by arêtes)
- which collects and compresses through gravity the snow
which falls into it. This snow collects and is compacted by
the weight of the snow falling above it, crushing the
individual snowflakes and squeezing the air from the snow.
Once the air has been squeezed from it the snow is turned
into extremely dense 'glacial ice'. This glacial ice will then fill
the névé until it 'overflows' through a geological weakness or
vacancy, such as the gap between two mountains. When the
mass of snow and ice is sufficiently thick, it begins to move
due to a combination of surface slope, gravity and pressure.
On steeper slopes this can occur with as little as 15 m (50 ft)
of snow-ice.
8.
9. •Snow line – it is the elevation above
which snow remains all year, varies
with different locations.
•Snow field – are found in low latitudes
only at high latitudes.
10. Types of Glaciers
Valley glaciers – also called alpine glaciers. Pilling
up of snow in mountain valleys above the snow line
may produce valley glaciers.Alpine glaciers, also
known as mountain glaciers or cirqueglaciers, form on
the crests and slopes of mountains. An alpine glacier
that fills a valley is sometimes called a valley glacier.
- a number of valley glaciers may also blend
together to form a huge piedmont glacier as they
move out onto a plain at the base of the mountains.
Continental glacier – is found only in Polar Regions.
This type of glacier covers the entire land
surface.Glacial bodies larger than 50,000 km² are
called ice sheets or continental glaciers.
11. CONTINENTAL GLACIER VALLEY GLACIER
The Baltoro Glacier in
the Karakoram,Baltistan,
Northern Pakistan. At 62 kilometres
(39 mi) in length, it is one of the
longest alpine glaciers on earth.
SAMPLE OF
CONTINENTAL &
VALLEY/ALPINE
GLACIER
12. MOVEMENT OF GLACIERS
The complete explanation for glacial
movement probably involves the fracturing of
ice, the flowing of ice under pressure, and
melting and refreezing, as well as other
processes not yet understood.
13. • 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.
14. Crevasses - are often more than a hundred feet
deep, and may be concealed by a thin crust of
snow which breaks at the slightest weight.
Tide-water glaciers – when the edges of
glaciers that reaches the shore. This is because
the rise and fall of the tide snaps off large
sections of the ice that float away as icebergs.
Tidewater glaciers are glaciers that terminate in
the sea. As the ice reaches the sea, pieces
break off, or calve, forming icebergs. Most
tidewater glaciers calve above sea level, which
often results in a tremendous impact as the
iceberg strikes the water.
15. SAMPLE OF CREVASSE AND TIDEWATER GLACIERS
Sightseeing boat in front of
a tidewater glacier, Kenai
Fjords National Park, Alaska
Crossing a crevasse on
the Easton Glacier, Mount
Baker, in the North
Cascades,United States
16. Glacial Erosion
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.
18. *
1. U-shaped valley – The characteristic cross section profile of a valley carved by glacial
erosion.
2. Hanging valley – A small valley that terminates abruptly high above a main valley.
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.
19. A Glacier carves a
U- shaped valley
Bridal Veil Falls in Yosemite
National Park flowing from a
hanging valley.
22. 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.
Moraine- An elongate deposit of glacial till.
23. There are several types:
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.
24. • Drumlin- A streamlined hill of till produced by
continental glaciers (the origin is not entirely
understood). Drumlins point in the direction of ice
movement.
• 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).
25. 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.
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
26. The Glacial Periods
A glacial period (or alternatively glacial or glaciation) is
an interval of time (thousands of years) within an ice
age that is marked by colder temperatures
and glacier advances. Interglacials, on the other hand, are
periods of warmer climate between glacial periods. The last
glacial period ended about 15,000 years ago;
The Holocene epoch is the current interglacial.
27. The first glacial period occurred about 800 million years
ago. Then there was a period of about 300 million years of
freedom from general glacial activity.
The second glacial period came about 500 million years ago
and was followed by a warm spell of about 300 million
years.
Then the ice sheets formed again to the third time about
200 million years ago.
The latest ice invasion took place only about 1 million years
ago. Our very distant ancestors were no doubt chilled and
forced to migrate by the advancing glaciers.
28. POSSIBLE CAUSES OF THE GLACIAL PERIODS
1. Variation in the amount of heat received from
the sun.
2. Topographical factors.
3. Melting of the Arctic ice.
29. A glacier moves as a solid rather than as a liquid, as is
indicated by the formation of crevasses (see crevasse). The
center of a glacier moves more rapidly than the sides and the
surface more rapidly than the bottom, because the sides and
bottom are held back by friction. The rate of flow depends
largely on the volume of ice in movement, the slope of the
ground over which it is moving, the slope of the upper surface
of the ice, the amount of water the ice contains, the amount of
debris it carries, the temperature, and the friction it
encounters. Glaciers are always in movement, but the extent
of the apparent movement depends on the rate of advance
and the rate of melting. If the ice melts at its edge faster than
it moves forward, the edge of the glacier retreats; if it moves
more rapidly than it melts, the edge advances; it is stationary
only if the rate of movement and the rate of melting are the
same.
