Transcript Landforms Created by Glaciers

Landforms Created by
Glaciers
Chapter 15.2
Glacial Erosion
1.Glacial Erosion
a. The process that formed the mountains
begins with a glacier still high in the
valley.
i. As a glacier wedges its way through a
narrow valley, it breaks off rock from the
valley walls, causing the walls to become
steeper.
ii. Blocks of rock are also pulled from the
floor of the upper valley.
Glacial Erosion
iii.A cirque is a bowled shape
depression created by these glacial
actions.
1.Cirque means “circus” in French, as it
refers to the circus like round depression
of a circus theater.
iv.Arêtes means spine in French, and
refers to the sharp and jagged ridges
that form between the cirques.
v. A horn is a cluster of several arêtes
that form a pyramid like peak.
Cirque & Arêtes
Glacial Erosion
b. When a glacier moves down a valley it
picks up many rocks ranging in size
from pebbles to boulders.
i. These rocks that are now being carried by
the glacier act as another erosion agent.
ii. As the glacier and rocks pass over the earth
they polish and round larger rock
formations.
Glacial Erosion
1. These rounded projections have a
smooth, gently sloping side facing the
direction from which the glacier came,
with the far side being steep and jagged
as rock was pulled away when the ice
passed over.
2. These rocks are called roches
moutonnees, which means “sheep rock”
in French, because they resemble the
backs of sheep.
Roches Moutonnees
Glacial Erosion
c. The shape of valleys are originally a
“V” shape. However, once a glacier
passes through them, it cuts them out to
a “U” shape. This is an easy way for
scientists to tell if the valley was carved
by a glacier.
d. A tributary glacier is a glacier that flows
into a larger glacier.
Tributary Glacier
Glacial Erosion
i. Tributary glaciers do not cut as deep
“U” shapes since they are much
smaller than the main glacier, and
when the ice melts they are left high
in the valley.
ii. These valleys formed from the melted
ice of a tributary glacier are called
hanging valleys.
Hanging Valley
Glacial Erosion
e.The erosion process of
continental ice sheets is very
different from valley glaciers.
i. Continental ice sheets generally
level landforms and produce
smooth, rounded landscapes.
Glacial Erosion
1. Existing valleys are gouged
out and deepened, and rock
surfaces are scratched and
grooved by rocks carried at the
base of the ice sheet. These
scratches and grooves run
parallel to the direction of
glacial movement.
Glacial Deposition
1.Glacial Deposition
a.Glacial deposition occurs when
valley glaciers reach lower
elevations or when climate change
melts continental ice sheets.
b.Glacial drift is the general term
given to all sediments deposited by a
glacier or by the meltwaters from a
glacier.
Glacial Drift
Glacial Deposition
i.When the glacier melts all of the
material in the glacier is deposited
onto the earth.
ii.Erratics are large boulders that
have been carried by the glacier
and do not match the composition
of the bedrock that they are now
on.
Glacial Erratic
Glacial Deposition
iii. Till is made of unsorted deposits of
rock material that is deposited from
sediments scraped off by the base of
the glacier or is left behind when
glacial ice melts.
iv. Stratified drift is material that has
been sorted and deposited in layers
by streams flowing from the
meltwater.
Till & Stratified Drift
Glacial Deposition
c.Till deposits are landforms
made from glacial till called
moraines.
i. Moraines are ridges of unsorted
rock material on the ground or on
the glacier. We will be discussing
five types of till deposits or
moraines.
Glacial Deposition
2. A lateral moraine is one that is
deposited along the sides of a
valley glacier, usually as a long
ridge.
3. A medial moraine occurs when
two or more valley glaciers join,
and their adjacent lateral moraines
combine.
Lateral & Medial Moraine
Glacial Deposition
4. Ground moraine is the unsorted
material left beneath the glacier
when the ice melts.
a.Much of the landscape in Ohio
is covered with ground moraine.
Glacial Deposition
4.Drumlines are long, low, tearshaped mounds of till, often found
in clusters
5.A terminal moraine is the till that is
deposited at the snout or front of a
melting glacier. They are belts of
small ridges of till with many
depressions that contain lakes or
ponds.
Drumline & Terminal Moraine
Glacial Deposition
6. In front of a terminal moraine, and
after meltwater has deposited its
small rock particles is a large
outwash plain.
a. An outwash plain is a deposit of
stratified drift, which usually
lies in front of a terminal
moraine and is crossed by many
meltwater streams.
Glacial Deposition
7. A kettle forms when a portion of
glacial ice is buried in drift, and
when the ice melts it leaves a
cavity in the drift, and often forms
lakes.
a. Kettles are mostly found in
outwash plains.
Kettle
Glacial Deposition
8. An esker is formed when
continental ice sheets recede and
long, winding ridges of gravel and
coarse sand may be left behind.
a. Eskers consist of stratified drift
deposited by streams of
meltwater flowing in ice tunnels
within the glaciers, and may
extend for tens of kilometers.
Esker & Ice Tunnel
Glacial Lakes
3. Glacial Lakes
a. Glaciers commonly form lake basins by
eroding out surface area, leaving
depressions in the bedrock, and
deepening existing valleys.
b. Glaciers also commonly form lake
basins by depositing till. Many lake
basins were created by the uneven
surfaces of ground moraine deposited by
glaciers.
Glacial Lakes
c.Another way glaciers form lakes is
when terminal and lateral moraines
block existing streams and create a
lake basin.
d.The Great Lakes are the result of a
combination of erosion and
deposition by continental ice sheets.
Glacial Lakes
i. Glacial erosion widened and
deepened broad river valleys
covered by ice sheet.
ii. Moraines to the south blocked off
the ends of these valleys.
iii. As the ice sheets melted, the
meltwater flowed into the valleys
and was trapped by the moraines to
form the Great Lakes.
Glacial Lakes
1. During the early stages of the ice retreat the
great lakes were much larger and drained to
the south. As the ice sheet retreated, the
lakes became smaller and the drainage
patter changed. Uplifting of the land, and
further ice retreat, reduced the Great Lakes
to their present size and established current
drainage northeast through the St.
Lawrence River.
Glacial Lakes
e. In areas where evaporation is
high and precipitation is low
lakes with high salt content can
be formed.
i. In the area where the ice age
Lake Bonneville once was is the
current, and much smaller Salt
Lake in Utah.
Glacial Lakes
ii. This lake became very salty due
to the fact that it had no
drainage, and the only way water
could leave was through
evaporation. When the water
evaporated, the salt was left
behind forming the current Salt
Lake.
Glacial Lakes
i. These high salt content lakes can
also be a location of valuable
minerals depending on the
dissolved minerals it contains.
1. Minerals can either be brought in
by streams or are the result from
the chemical and biologic
processes occurring in the lake.
Glacial Lakes
i.The salt deposits left in the dry beds of
ancient salt lakes often contain
valuable minerals such as borax,
which is used as a cleaning material
and the manufacturing of glass and
steel.
1. Currently the dry lake beds of the
Mojave Desert in California contain
borax.