glaciers & glaciation
Types of glaciers
How do glaciers move?
Glacial landforms
Causes of glaciation
types of glaciers: valley or alpine glaciers
found in mountainous
regions
flow in valleys that were
previously occupied by rivers
Frequently merge with
other valley glaciers
Lengths vary from less than
a kilometer to tens of
kilometers
Highly effective as erosional
agents
Continental ice sheets
What’s it like to be on a continental ice sheet?
Here’s a typical view.
These ice sheets develop in part due to the low levels of solar
radiation reaching the Earth’s polar regions. (It’s COLD!)
Continental ice sheets cover about 10% of Earth’s land area.
In general, the ice is thickest near the center of the ice
sheets and flows outward in all directions from there.
Where ice flows over ocean water ice shelves are formed.
Shelves become thinner seaward and often break off forming
icebergs.
Ice shelves are sustained by ice from the mainland as well as
freezing seawater from below.
ice sheets on Antarctica & Greenland
What would happen if the ice melted?
Glaciers and ice sheets contain 2% of the world’s total
volume of water (fresh plus salt).
Ice sheets contain over 2/3 of the world’s fresh water.
If they melted, sea level would rise 60-70 meters! Consider
what would happen to coastal regions and the major
metropolitan areas located near them.
What does that mean in the United States?
It all starts with a few snowflakes
Here are some glacialogists collecting
samples. The snowflakes shown are
photographed shortly after they fell and
accumulated on the glacier.
Step 2: conversion of snowflakes into firn
Is this an SEM
image of firn or ice
worm eggs
Cross sectional view showing layers of
snow and firn in a snow field.
Illustration on left shows
density of snow, on right
density of firn.
What do you think a
picture showing the density
of ice would look like?
What does glacial ice look like?
Is glacial ice a mineral?
Solid?
Naturally occurring?
Inorganic?
Definite composition?
Glacial ice is interlocking
crystals of solid H2O that
form once the ice and
snow thickness reaches
50 m
Note the growth
patterns in the glacial ice
above
Definite internal structure?
What makes glaciers and ice sheets flow?
Is a glacier homogenous throughout it’s depth?
Upper 40 meters forms the rigid zone
Crevasses form here as glacier stretches to flow over
bumps in a valley
What is the maximum depth of a crevasse?
Characteristics of the plastic zone
The plastic zone begins
at a depth of 40 m
Bonds between layers
of ice are weaker than
those within a layer,
thus the layers flow
over each other
Basal slip also
contributes to the
movement of a glacier
Melt water lubricates
the bedrock allowing
the glacier to slip down
the valley
How fast do glaciers flow?
Flow rates vary
considerably from one
glacier to another
Ex. Byrd Glacier,
Antarctica has flow
rates of about 2 m per
day
Flow is often not
smooth and continuous
Surges occur, rates of
up to 100x normal may
occur
Glacial budgets
Zone of accumulation is
separated from zone of
ablation by equilibrium
line or snowline
zone of accumulation
amount of snowfall is
greater than melting on
an annual basis
Zone of ablation
(wastage) melting is
greater than snowfall on
an annual basis
Glacial budget is the
balance between
accumulation and ablation
The roar of the
thunderous calving
of a glacier
Glaciers and ice
sheets waste in two
ways, melting and
calving
Calving is the
breaking off of
large pieces of ice
at the glaciers
terminus
Calved pieces form
icebergs where the
glacier reaches the
sea or a lake
How do glaciers alter landscapes?
Glaciers alter landscapes significantly in two ways
Glacial erosion creates many new features
Glacial deposition also creates new landscapes
Let’s look at some of the features created by glaciers
How do glaciers erode? plucking
Plucking occurs when
glaciers flow over
fractured bedrock
Loose rock is then
incorporated into the ice
Frost wedging increases
the effectiveness of
plucking
Glaciers aren’t too
particular about the size of
the sediment transported
In the illustrations we see
a boulder about to be
plucked and a slope that
shows evidence of
plucking
How do glaciers erode? abrasion
Ice containing sediment
acts as sandpaper as it
flows over bedrock
Striations are long
grooves or scratches
created as ice flows
over bedrock
Landforms associated with glacial erosion
arête & truncated spur
glacial trough
hanging valley
Erosional features
horn, cirque, arête
pater noster lakes
Erosional features
tarn lake in a cirque
col, cirque, arêtes
Erosional features
roche moutonnee
fjord
horn
Glacial drift
All sediments of glacial origin are
collectively known as glacial drift
Two categories of drift
Till – sediment directly deposited by
glacier
Stratified drift – sediment deposited
by glacial melt water
Glacial till & glacial erratics
Deposited directly by
glacial ice
Poorly sorted
Grains often show
evidence of abrasion
Erratics – boulder sized
grains deposited
directly by glacial ice
valley/alpine glaciers: moraine deposits
Glacial ice erodes the valley
walls incorporating large
volumes of rock debris to the
edges of the ice
When the ice melts, this debris is
deposited along the valley walls
forming lateral moraines
medial moraines
When two tributary
glaciers merge, their
lateral moraines merge
to form a central
medial moraine
By counting medial
moraines, glaciologists
can determine the
number of tributary
glaciers that have
merged to create a
larger glacier
terminal, end or recessional moraines
A ridge of till that is deposited at the terminus of a glacier or ice
sheet during a time when the glacier is in equilibrium (ablation
equals accumulation)
Terminal or end moraines are only different from recessional
moraines in that they mark the furthest extent of a glacier’s
terminus
Terminal, end or recessional moraines
ground moraines
A relatively flat layer
of till deposited as
the terminus of the
ice recedes
Ground moraines
tend to level the
surface, filing in
depressions and
clogging stream
channels
They are common
with either
valley/alpine
glaciers or ice
sheets
drumlins
Hills of glacial till
deposited by a glacier
or ice sheet
Range in height from
15 to 50 meters
May be up to 1 km long
Oblong in shape
Steeper side faces the
direction the ice
advanced from, gentler
slope points direction
ice flowed toward
Landforms of stratified drift
Glacial meltwater sorts and
deposits sediment
Commonly sand & gravel
sized grains
Rock flour is transported as
suspended load
Outwash plains are
associated with ice sheets
Valley trains are
associated with valley
glaciers
Broad, flat surface
covered with stratified drift
deposits
Kettle lakes, kames, eskers
Kettle lakes form when
blocks of ice remain lodged
in drift and eventually melt
in the depression they
formed
Eskers are ridges deposited
beneath glacial ice by subglacial streams