Transcript Document

Glaciation
Glaciation
A glacier is an accumulation of ice, water and rock
debris or sediment.
It is a large enough quantity of ice to flow with
gravity due to its own mass.
Glaciers flow very slowly, from tens of meters to
thousands of meters per year.
The ice can be as large as a continent, such as
the ice sheet covering Antarctica. Or it can fill a
small valley between two mountains; a valley
glacier.
Causes of glaciation periods?
In Antarctica, glaciers occur because the continent is
located in a polar region.
In the Rocky Mountains glaciers are caused by the
coolness of the atmosphere at higher altitudes.
The Milankovitch Theory (100,000 year
cycles), suggests that Ice Ages were caused by
variations in the Earth's orbit. This theory considers:
Eccentricity - The variance of the Earth's orbit from nearly
circular to elliptical
The Inclination of the Earth's axis - how tilted the Earth
is with respect to the sun
Precession of the Equinoxes - Sometimes, the wobbling
of the Earth as it moves around the sun can cause winter to
occur at different times of the year.
Types of glaciers
Continental Glaciers - Continental glaciers
evolved during the Ice Ages. These glaciers
are large sheets of ice, which cover vast
areas and are unconfined by topography. For
example, during the last Ice Age, ice covered
all of Canada, and even parts of New York.
Alpine (Valley) Glaciers - These glaciers
form and flow within mountain valleys. They
are especially common in high altitudes areas
such as the Rocky Mountains.
How do glaciers move?
One of the unique properties of glaciers is the way in
which they move: their weight causes them to flow
like a very slow moving river. When a glacier
becomes thick enough (about 18 meters thick), it
becomes so heavy that it begins to deform.
The weight of the glacier, as well as gravity, causes
the glaciers to flow very slowly. When flowing, the
underside of the glacier is slowed by friction (due to
contact with the ground beneath), while the surface
of the glacier moves much faster.
This causes a conveyor belt like motion down a
slope.
Glaciers can advance or retreat but the actual ice is
always moving down slope.
Glaciation - mechanisms
accumulation - material added
to the mass of the glacier or ice
sheet (snow, rain).
accumulation zone - the area of
the glacier or ice sheet where
material is only added; no mass
is lost. Usually this area is near
the top of the glacier or ice
sheet.
ablation - the process of
removing material from the
glacier or ice sheet (melting
at the surface or the base,
evaporation, calving). In
Antarctica, most ablation
occurs by calving ice off the
ice sheet and ice shelf
edges.
ablation zone - the area of
the glacier or ice sheet where
more mass is being lost than
gained. In Antarctica, the
ablation zone on most
glaciers is small or at the
edge of the ice.
Glaciation - mechanisms
http://www.glacier.rice.edu/land/5_whatisaglac
ier.html
Glaciation - mechanisms
http://www.glacier.rice.edu/land/5_ic
eofallshapes.html#anchor6097245
Calving!
Glaciation – Erosional landforms
Erosional subglacial
features are those
features created
beneath the ice by the
glacier removing rock
material and
transporting it away.
They can be large scale,
such as glacial valleys
carved through the
mountains, or small
scale, such as the tiny
striations engraved in
pebbles!
Glaciation – Terms
Abrasion - mechanical
grinding or wearing away of
material.
Striations - Grooves or
scratches cut in the bedrock by
the bottom of the glacier
Till - Material picked up and
carried by the glacier before
being directly deposited from
the ice.
Erratics -Transported boulders
of a different rock type than the
bedrock.
Terms - Alpine
Cirques are the bowl shaped depressions found at
the head of glacial valleys. For most alpine glaciers,
cirques are the areas in the alpine valleys where
snow first accumulated and was modified into glacial
ice.
Horns are pyramidal peaks that form when several
cirques chisel a mountain from three or more sides.
The most famous horn is the Matterhorn found in the
Swiss Alps.
Arêtes are the narrow serrated ridges found in
glaciated alpine areas. Arêtes form when two
opposing cirques back erode a mountain ridge.
Terms - Continental
Moraines are ridges of sediment that
are deposited perpendicular to glacier
flow near the terminus of a glacier.
Eskers are sinuous ridges of sand and
gravel deposited in or under ice in a
meltwater tunnel.
Kames are hills of sediment that are
commonly found near kettles.
Kettles are depressions that were
formed when a buried ice block melts
Glaciation – erosional landforms
Roches Moutonnees
have a smooth side
where the ice abraded
and a jagged or rough
side where the ice
plucked the rock as it
flowed over the
obstacle.
Roches moutonnees are
excellent glacial flow
directional indicators.
http://www.glacier.rice.edu/land/5_gl
aciallandforms.html#anchor843709
A moulin or glacier mill is a narrow, tubular chute, hole
or crevasse through which water enters a glacier from the
surface. They can be up to 10 meters wide and are
typically found at a flat area of a glacier in a region of
transverse crevasses
Glaciation – depositional landforms
Depositional features
are features created by
the glacier depositing or
releasing sediment.
They vary in scale from
thin ground cover to
huge terminal moraines
such as Cape Cod.
Depositional features
include landforms
directly created by ice,
but also include features
that are created by
glaciation indirectly,
such as deltas and
fans.
Glaciation – depositional landforms
Subglacial Moraines
Moraines are
accumulations of glacial
material (till) that have
surface expression.
Based on that broad
definition, there are
several different types of
moraines. Subglacial
moraines, made of till,
take on several shapes.
.
http://www.glacier.rice.edu/land/5_gl
aciallandforms.html#anchor843709
Glaciation – depositional landforms
Lateral Moraines and
Medial Moraines
Lateral moraines and
medial moraines are
not subglacial
features, but they form
in the glacial
environment. They
occur next to the
glacier, and are in
contact with the ice.
Glaciation – depositional landforms
Moraines
Moraines are
accumulations of glacial
material (usually till)
shaped by the ice. Some
moraines form under the
ice, others form in front
of the ice.
.
Glaciation – depositional landforms
Moraines con’t
Terminal or end moraines
can be quite large. They are
the result of all the material
carried by the glacier to the
glacier front, much as a
bulldozer pushes and
scrapes material into a pile.
Terminal moraines mark the
position of the ice where it
was most extensive.
Interlobate moraines are
formed between two lobes of
ice – such as the Oak Ridges
Moraine in Southern Ontario
http://www.science.uottawa.ca/~users
/clark/quat2333/Morin/pres.html
Alpine features
Continental
Features
Glaciation – Where Are Glaciers Today?
In general, glaciers exist where ever the accumulation of frozen
material is greater than the ablation (or loss) of frozen material. Most
of us probably think of cold places, such as Greenland or Antarctica
when we think of glaciers. But glaciers also exist in warmer places,
such as New Zealand, Chile, and even pretty close to the equator in
Africa!
.
http://www.glacier.rice.edu/land/5_w
armice.html
Glaciation: What does the Future hold?
.
http://www.glacier.rice.edu/land/5_ic
eofallshapes.html