This lecture will give you a brief introduction to glaciers and helps you to better understand the glaciers.

1. Glaciers &
Glaciation

2. OUT LINE
• Origin of glacialice,
• Types of glaciers,
• Movement ofglaciers,
• Glacial erosion, (covered)
• Deposition by glaciers(land
forms)
• Causes of Glaciation

3. Glaciers
• a thick ice mass that originates on land from the
accumulation, compaction, and re-crystallization of
snow.
• Agents of erosion – acquire, transport and deposit
sediment
• Occupy ~10% of landarea
• “Interrupts” hydrologic cycleby “locking up”water
Theterm glacier does not include icebergs, seaice, or immobile snow fields in
mountainous areas.

4. Origin of GlacialIce
• Accumulation of snow - snowfields grow in areasabove
the snow line where more snow accumulates in the
winter than melts during the summer. Freshly fallensnow
hasabout 80%void space.
• Formation of ice granules - assnow accumulates and
gets thicker, sublimation (transformation of solid togas)
and pressure change it into firn (icegranules).
• Formation of glacial ice - with further accumulation,
compaction and pressure melting (released water that
refreezes to cement ice granules together) cause firn to
be transformed into glacial ice (mass of interlocking
crystals). Ice has only about 10% void space. When ice
reaches athickness - 40 meters, flow and form glacier.

5. Glacier Types
1.Valley (Alpine)
• Found in mountainousareas
• Smaller than icesheets
• Lengths greater than widths
• Only cover a smallregion
• Transform V-shaped valleys into U -shapedvalleys

6. Alpine Glaciers

7. GlacierTypes
2.Ice sheets (Continentalglacier)
• Large scale – cover 10% of Earth’sland
• Found in polarregions
–Greenland – 1.7million km2
–Antarctica – 13.9million km2
3.Ice caps - similar to continental glaciers, but smaller in size
(<50,000 km2), these ice masses may form by valley glaciers
merging together or on fairly flat terrain at high latitudes.

8. Continental Glaciers

9. Glaciermovement
•Gravity primaryforce
•Entire ice sheet moves 5to 50m/yr
– Plastic flow – flowing solid
– Basal slip – movement over bedrock
•Fastest movement within thecenter
•Friction Slows down thesides
valley glaciers move faster than continentalglaciers

10. Rates of GlacialMovement
• Valley Glaciers- rates vary from centimeters per day to tens of
meters per day.
– The steeper the slope, the faster the rate of movement.
Larger ice massesmove faster than smaller icemasses.
– In avalley glacier, ice moves fastest at the uppercenter
part of zone of plasticflow.
– Basalslip is most rapid in warmer months and canproduce
brief periods of rapid movement called surges. Surgescan
be produced by unusually heavy precipitation and by
avalanches loading the upper part of avalleyglacier.
• Continental Glaciers - average rate of movement is afew
cm/day or afew m/day.
– Flow rates are fastest in the zoneof accumulation anddecrease
below the firn line toward the margins.
– Thicker ice sheets have higher flow rates than thinnerones.
– Theseglaciers show little basalslip and may be frozen to the
underlying surface.

11. Glaciermovement
20meters
100meters

12. GlacierBudget
In - Zone ofaccumulation
Snow accumulates and forms ice >melting
Outer limit is thesnowline
Out – Zone of wastage
ablation – general term for loss of ice or snow
from a glacier >accumulation
1. Sublimation
2. Melting
3. Evaporation
4. Calving -icebergs

13. •
•
• s
If ice formationis greater than ice loss –
glacier advancesdownslope
If ice formation is lessthan ice loss –glacier
retreats upslope
If ice formation is =ice loss – glacier positioni
stationary
Zoneof Accumulation Zoneof Wastage
Glacier budget

14. Erosion by Glaciers
•volume and speed determines
amount of erosion.
•erodes slightly more effectively
than water.
•plucking and abrasion (rock-tipped
blade).
Creates Rock flour – very fine-
grained material
Creates Striations – grooves
scratched in bedrock that
indicate direction of ice
movement
•Continental glaciers remove
all soil, plants, and small hills.
•Alpine glaciers change V-shaped
valleys to U-shaped.

18. Transportation
by Glaciers
•will move material of all sizes,
from glacial flour to massive
boulders.
•Slow transport.
•Water in, on, and under
glaciers (pluvial processes)
moves much sediment as well.

19. Deposition by Glaciers
•drift is any material deposited by
glaciers or their meltwater.
•Till is that unsorted material that is
deposited directly by ice.
•Moraines are linear features
deposited at bottom or along sides
of glaciers.
•Glacial erratics are enormous
boulders transported and deposited
by glaciers, often far from their
source region.

20. Alpine Glaciers

24. Moraines

26. Continental Glaciers or Ice Sheets

27. Continental Glaciers or Ice Sheets

28. Outwash plains - area beyond the margins of acontinental glacier where
meltwater (asbraided streams) deposited sand, gravel, and mud washed out from
the melting ice. When confined to amountain valley, outwash is called avalley
train.
Kettles - depressions in deposits of glacial drift formed where ablock of ice was
partially buried, and then melted. Thedepression canfill with water to form a
lake. Kettles form in outwash plains and inend moraines.

29. Causesof Glaciation
• Full Reasoning is notknown
• Theory of Glaciation needs toinclude:
– Interglacial periods – periods of warm climate
separating periods of glacialadvancements.
– Theonset of a period or stage of glaciation is due to
a change in Earth temperature and circulation. It is
generally accepted that a globaldecrease of 40 to 5
0C,especially during the summer, and a substantial
increase in the amount of snowfall in subarctic and
arcticregions is necessary for the onset of a glacial
episode.

31. Causesof Glaciation
• Full Reasoning is notknown
• Theory of Glaciation needs toinclude:
– Interglacial periods – periods of warm climate
separating periods of glacialadvancements.
– Glacial episodes in the Paleozoic (200-300mya)
and Precambrian time (700mya).

33. Causesof Glaciation
• Full Reasoning is notknown
• Theory of Glaciation needs toinclude:
– Interglacial periods – periods of warm climate
separating periods of glacialadvancements.
– Glacial episodes in the Paleozoic (200-300mya)and
Precambrian time (700mya).
– Earth’saverage global is 140C,in the geologic pastit
was 220C – Glaciation requires a temp. of about 10
0C.
– Continental glaciers originate in polar orelevated
land.
– Sufficient precipitation needs tooccur.

34. Milankovitch cycles
• Several theories have been proposed for such a change
in climate -- reductions in solar radiation due to
meteorite collisions with the Earth, increased
volcanism, the shifting location of continents, and the
uplift of vast mountain regions. Milutin Milankovitch
proposed one of the most significant theories to
account for climate change by variations in Earthorbit.
• Earth’sorbital changes controls itsclimate
• Eccentricity
– Measure of the noon circularityof Earth's orbit
– Cycleis about 100,000years

35. The degree of deviation of the orbit from aperfect circular
path, is thought to causethe necessary change in
insolation to decrease globaltemperatures.

36. Milankovitch Cycles
Discussion: cool summers and wet winters
Moisture content of airmasses
100,000years

37. Milankovitch cycles
• Eccentricity
• Inclination
– Thechanges in the axial tilt (22 0 to 24.50) of the
Earth
– Thegreater the tilt the greater the contrast
between summer and wintertemperatures
– Cycle is about 44,000years

39. 41,000years
ColdDry Winter
Hot Summer
Warm WetWinter
Cool Summer

40. Milankovitch cycles
• Eccentricity
• Inclination
• Precession
– Thewobble of the Earth as it spins on its axis
– Cycle is about 22,000years

42. 25,700years
Discussion: Perihelion and Aphelion

43. Milankovitch cycles
• Main effect of cycles which alters the amount of
insolation reaching the surface of the Earth resultantly
change the contrast in the temperature of the summer
and winter.
•
• Glaciation would occur when the summertemperature
is closer to the winter temperature, but winter
temperature are not colder thanusual.
• Rather the mild summers melt less ice than isreceived
in thewinter.

45. Mechanisms for PastGlacialPeriods
• Pleistocene glacial and interglacial episodes are
correlated with variations in the Earth’s orbitat
21 ka, 41 ka, and 100 ka. Discovered by M.
Milankovitch in 1921.
• General absenceof glacial periods in the pastis
NOT explained by Milankovitch cycles.
• Other mechanisms:
– Changesin CO2content in the atmosphere (large
volcanic eruptions canlower global temperature).
– Movement of the continental landmasses bytectonics.
– Changesin oceanic circulation asaresult of both
atmospheric and tectonic processes.

46. Indirect Effects of Glaciation
• Causedimportant climatic changes. Pluvial lakesformed in desert
areas,showing cooler and wetter conditions. Proglacial lakesformed
from glacial meltwater. Deposits of loess (wind-deposited dust)were
laid down in temperate areas. Someareaswere much drier due to
cooler temperatures causinglessevaporation from the oceans.
• Changedsea levels.
• Forced plants and animals to migrate.
• Diverted stream drainage patterns and causeddowncutting bystreams
e.g. Riversin the northern part of North America once drained
northward, but were blocked by glacial ice. Lowered sealevelcaused
streams to erodedownward.
• Weight of ice depressed continental crust. Plastic asthenosphereacts
like a"mattress", asin someplaces, crust wasdepressed by 300
meters.After ice melted, the crust hasbeen gradually rebounding
(isostasy)

47. Thanks
Any Question?