Glaciers Natures Bulldozers

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Glaciers Natures Bulldozers Powered By Docstoc
Studies in Ice and Snow
The   “cryosphere”, comes from the Greek word,
meaning frost
It is the part of the hydrosphere that is frozen

   Permafrost (permanently frozen ground)‫‏‬
   Sea Ice
Only recently has been discovered as a key to
understanding climate, oceans, and the life system.
With  increased awareness of of climate change, more
studies are done of the cryosphere
We tend to forget about how much ice there is in the
high latitudes
 Yet the cooling effect of these areas have a
 profound effect on global climates and ocean
 on the ice circulation
 The average temperature of the earth has

 warmed up by 0.6oC over the past century
  Doesn't sound like a lot, but has a huge
  impact on the entire system
   Extent:
    ◦ 47 million km2 at its max.
    ◦ 5 times the size of Canada
    ◦ Located mainly in the Northern Hemisphere
   Description:
    ◦ Snow lying on the ground
   Impact on the Atmosphere:
    ◦ Snow reflects 80% of incoming solar radiation so
      the area remains cold
    ◦ If snow cover melts, it will become much warmer
      because more solar radiation changes to heat
   Active Layer: soil that melts & refreezes daily
    or seasonally – as thin as 10cm in continuous
    permafrost, up to2m thick in discontinuous
   Dramatic warming in Arctic is making active
    layer much thicker & releasing tons of CO2
   Talik: body of unfrozen ground within
    permafrost, eg. Under a lake, important for
    movement of groundwater
   Extent:
    ◦ 23 million km3 (nearly 24% of the earth’s surface
    ◦ Up to 500m thick
   Description:
    ◦ Water saturated rock or soil that remains below
      freezing for more than 2 years
   Impact on the Atmosphere:
    ◦ Increased methane from thawing permafrost
      would increase climate change
   Extent:
    ◦ 14-16 million km2 in the Arctic and 17-20
      million km2 in the Southern Hemisphere
   Description:
    ◦ Frozen ocean water in the form of pack ice
   Impact on the Atmosphere:
    ◦ Regulates heat and moisture in polar regions
   Impact on the Biosphere:
    ◦ Polar bears rely on pack ice to hunt for seals
    ◦ The absence of sea ice in Hudson’s By could
      result in the bears becoming expurgated there
   Extent:
    ◦ Are located on Antarctica, Greenland, and
      Ellesmere Island as well as on some mountain
      peaks and alpine valleys
   Description:
    ◦ Snow that falls in winter and fails to melt in
      summer, resulting over time in a glacier
   Impact on the Atmosphere:
    ◦ Air is colder over glaciers
   Impact on the Biosphere:
    ◦ Virtually no plants or animals live on glaciers
   30% of earth’s surface covered by ice sheets
    (only 11% covered today!)‫‏‬
   In near-glacial environments – constant
    freeze/thaw cycle effects on landscape
   Permafrost – ground that is permanently
    ◦ Continuous: poleward of –7oC mean annual
      isotherm – all surfaces frozen except under water –
      avg. 400m thick, up to 1000m thick
    ◦ Discontinuous: poleward of –1oC mean annual
      isotherm – thinner than continuous, especially on
      south facing slopes
   As early as 2.3 B years ago, ice covered much
    of Earth, and off and on since then
   Most important Ice Age was Pleistocene
    Epoch, 1.8 M years ago until 10K years ago
   Glacial – period when glaciers expand from
    poles – cooler temps, lower sea level
   Interglacial – period when glaciers recede:
    warmer temps, higher sea level
   Ice core samples
    suggest more than
    the known 4
    glaciations – show
    more cool, glacial
   Oxygen isotopes
    O-16 to O-18 in ice
    cores can indicate
    relative warmth of
    climates over 1 M
    yrs ago!
•    Summer temp (melting) is key to Glaciation
•    Possible Factors:
    1. Variations in solar radiation (dust, sunspots…)‫‏‬
    2. Reduced carbon dioxide (escaping heat)‫‏‬
    3. Increased volcanic activity (reflective dust)‫‏‬
    4. Variations in Earth-Sun geometry (axial tilt,
       shape of orbit, rotation)‫‏‬
   Dominant theory of causes of glaciation, based
    on Earth-Sun geometry:
    ◦ Orbital eccentricity: strongly elliptical orbit puts Earth
      farthest from Sun in summer, cooling it (100,000 yr
    ◦ Tilt obliquity: Earth’s tilt varies from 22.1o to 24.5o –
      less tilt means lower angle Sun and less insolation at
      poles, thus cooler summers (41,000 year cycle)‫‏‬
    ◦ Orbital precession: wobbles of Earth’s axis – North
      Pole may point towards Sun at farthest point of orbit,
      creating a cool summer (26,000 year cycle)‫‏‬
   Glacier – slowly moving mass of dense ice
    formed by gradual thickening, compaction,
    and refreezing of snow & water over time
   After summer melt, some snow left over
   With weight and partial melting, snow turns
    to Firn, crunchy transition from snow to ice
   Further compaction, ice crystals align,
    become dense glacial ice which flows slowly
   At least 40 m thick to become glacier
   Glaciers move through internal deformation
   Interior of glacier like malleable plastic
   While edges of are solid
   As long as more is added than melted each
    year the glacier will continue to move.
  Two types of glacier:

         Alpine                          Continental
Their movement is mainly            They move due to their
      due to gravity.                    own weight.

     Some still exist in the        The last remaining can be found
western cordillera and the Arctic     in Greenland and Antarctica
   Alp Glaciers
    ◦ Ice Cap: Continuous sheet of ice covering entire
    ◦ Ice Field: Buries all but tallest mountains – can be
      very thick
    ◦ Alpine Glacier: Flows down valleys away from high
   Huge ice masses covering a large part of a
    continent or large island – also called ice
   More than 3000 m deep in places
   Covers most of Antarctica and Greenland
   Weight of ice presses lithosphere down into
    asthenosphere, called isostatic depression
Isostatic rebound…

  The Earth’s crust is depressed as a result of the weight of
   the ice. When the ice melts the surface slowly bounces
                  back. It is still going on!
   U-Shaped Valley
   How Formed:
    ◦ Before glaciation,
      mountain valleys are
      narrow and V-shaped
    ◦ Glaciation erodes V-
      shaped valleys into U-
      shaped ones
    ◦ Widening, deepening,
      and smoothing them
   A blunt-ended ridge of
    rock jutting from the
    side of a glacial trough
    or valley.
   How formed:
    ◦ Result from a glacier
      flowing around sharp
    ◦ In the process shearing of
      pointed spurs of land that
      extend into the valley
   A valley drops steeply
    from high levels, feeding
    into a deeper main valley
   How formed:
    ◦ The degree of glacial
      erosion depends on ice
      thickness, the main glacier
      cut their valleys much
      deeper than the smaller
    ◦ After the glaciers recede,
      the valleys of the smaller are
      perched above the main
    ◦ Rivers flowing through
      produce a waterfall.
   A deep, steep-sided sea
    inlet where mountains
    met the ocean
   How formed:
    ◦ Result when drowned
      glacial troughs were
      submerged as the ice left
      the valley and the sea level
      rose, flooding the valley
    ◦ Depths may exceed 1000m
   The point from which a
    glacier originally grew
   How form:
    ◦ Origins of them is not
      totally clear, but scientists
    ◦ Formed when, the head of
      a glacier erodes backwards
      into the mountainside,
      hollowing out a large
    ◦ Sometimes a small lake
      (tarn) could be found at
      the bottom.
   How formed:
    ◦ Depressions are formed
      when a glacier erodes
      rock areas of different
      strengths as it moves
      down the valley.
    ◦ When the glacier retreats
      the depressions fill with
   A gap or pass from
    one valley to another
   How formed:
    ◦ When two glaciers occupy
      opposite sides of a
      mountain ridge, the
      common back wall between
      the cirques may be
      eliminated as plucking and
      frost wedging enlarge each
    ◦ The two glacial troughs may
      merge to create a gap from
      one valley to another.
   As isolated spire of
   How formed:
    ◦ Caused by the
      enlargement and
      convergent of a group of
      cirques around a single,
      high mountain
   A narrow, knife-like
   How formed:
    ◦ Caused by the growth of
      cirques on opposite
      sides of a ridge of rock
    ◦ As cirques grow, the
      divide between them is
      reduced to a very
      narrow, knife-like ridge.
      Roche Moutonnee: rounded              Glacial Erratic

        hill, gradual on side toward
        direction from which glacier

Glacial Abrasion       Glacial Striations
                                            Roche Moutonnee

  An erratic is a large boulder that is carried by
  the ice to a spot where it is dropped. They are
  easily spotted, since they are usually unlike the
  rock around them.
 When rocks are carried
 in the bottom of a
 glacier they act like
 cutting tools. They
 carve long grooves in
 the bedrock as they
 move. The direction of
 these grooves shows
 which way the glacier
   Glacial Till:
    ◦ This is the material picked up and carried
      by the glacier. It is made up of everything
      from very fine particles of sand, to huge
Till Plain
 When the ice melts and leaves a layer of till behind, it is
 called a till plain. It is flat or gently rolling. They are very
 useful as farmland, due to the rich deep soil left behind.
•These are egg shaped hills that
usually occur in clusters.
•They are used for farming due
to the soil deposits, and are also
mined for gravel.
•How formed:
    •The steep side faces the
    direction from which the ice
    sheet advanced, while the
    gentler, longer slope points
    in the direction of the
    movement of the ice.
 A long meandering ridge of sand and gravel deposited by water flowing
 under a glacier or ice sheet.
 How formed:
          When a meltwater river flows as a channel through a stagnant
 piece of glacial ice. The meltwater stream channel can form on the
 surface of the ice, but is mostly found at ground level or with in the ice,
 where it deposits its sediment in the channels.

                                Eskers mark the
                                former beds of
                                water streams.

                               They are discontinuous
                               because streams deposit
                               sediments only in certain
                               places along their course.

Kames are steep mounds or
conical hills built by material
dropped in holes in the
material is dropped on the
 Kettle Lakes
Blocks of ice get

They are buried by

They melt and form
lakes called kettle
Kettle Lakes
 Moraine is an accumulation of
 boulders, stones, or other debris
 carried and deposited by a glacier
   How formed:
    ◦ As a glacier melts, the material collected by the
      glacier are deposited on the valley floor.
   Moraine types:
    ◦ End: Mark the former position of the glacier's
    ◦ Terminal: along front of former glacier, marking
      the farthest advance of a glacier
    ◦ Recessional: formed as glaciers recedes
    ◦ Ground: irregular deposition as glacier recedes,
      often appear as gently rolling hills or plains.
    ◦ Lateral: along former edges of glacier
    ◦ Medial: between 2 glaciers
   Since mid-1800s glaciers have been
    receding, both alpine and continental
   Alps, Parts of Andes, Mt. Kilimanjaro melting
   Thousands of sq km of Antarctica &
    Greenland ice sheet lost over last 30 yrs due
    to warming
   Melting area of Greenland has increased
    rapidly since early 1990s
   Migration of animals and plants
   Rebounding upward of the crust
   Glaciers are melting, there is a decreasing
    amount of snow cover
    ◦ Worldwide change in sea level
   Icebergs are more common
   Permafrost in melting
   Wetter climates in the deserts - vast lakes
   Polar Bears are running out of food

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