ESS 203 - Glaciers and Global Change
Monday January 23, 2017
Outline for today
•  Volunteer - today’s highlights on Wednesday_________
•  Highlights from last Friday– Claire Komori
•  Viscous flow of glaciers
•  Crevasses on glaciers.
•  Water in glaciers.
This week:
•  Water, sliding
•  Outburst floods
•  Ice Age World
Next Week
•  Objectivity in science
•  Midterm #1
Quiz #1 Wed Feb 1
•  I have posted 6 study questions.
•  The Quiz will be 3 of these questions.
•  A really good study method is to work with classmates,
write down, compare, and improve your answers to the
6 questions.
•  I have set up an online poll (Doodle) where you can
enter times that you could join a study session (or
sessions) (or parts of a session) Th-Fr-M-T.
http://doodle.com/poll/8gaii4ig59vzkn97
•  I will compile your answers on Wednesday morning,
and look for some rooms at your best times.
•  You can also set up times on your own, e.g. with
classmates and Lab partners.
ESS 203 - Glaciers and Global Change
Writing assignment due Wednesday
Now is a good time to decide which question(s) you
will try first, and share with peers informally or at
discussion sessions …
•  Write out your current best answer to one Quiz study
question that you will take to a study session.
•  I won’t assign a grade to your preliminary answer. But
it’s a C/NC contribution to class participation.
•  It’s for your own good. Trust me. ☺
My head hurts from all those numbers …
In Lab you were able to use elementary-school
arithmetic (multiplication, addition, …) and a few facts
from everyday life experiences, to get some initial
answers to questions where initially you may have had
no idea.
•  This approach to problems works in all areas of life.
“Every successful innovation starts with an estimation.”
Curious Scientists find evidence of glacier
behavior
Based on the Blue Glacier video, you worked with your
group to identify and describe lines of evidence to
support or refute
1.  Viscous flow
2.  Brittle fracturing
3.  Frictional slip
Perspectives on Flow and Change
•  Kinematic perspective
•  Dynamic perspective
•  Both of these ideas are useful for understanding
steady flow or changes, and for predicting flow
and changes in many other systems where
inventory matters (besides glaciers ☺).
Kinematic Perspective
Until now, we have looked at glacier flow from a
kinematic perspective. •  How much volume of ice must
Input (snow)
Output
(ice flux)
Gate
a glacier carry by flow past
any gate in a year, (ice flux)
(any gate, not just gate at
ELA) in order to evacuate a
volume of ice equivalent to all
the accumulated snow or ice
from upstream in a year?
•  Or if the flux carried
doesn t equal the total
upstream accumulation,
how fast does the
glacier thicken or thin?
Dynamic Perspective
Glaciers flow by Quasi-viscous deformation in
response to applied forces.
•  How fast does a glacier flow when it has a
particular shape (thickness and slope), a certain
softness (temperature), and is driven by certain
forces? (For example, gravity.)
•  If you pile up a bunch of ice, it is going to move if
gravity can pull it down a slope.
•  The flow speed is not necessarily determined by
the upstream accumulation or ablation pattern.
Later, we can combine the two perspectives to
see whether a glacier is growing or shrinking.
What Drives Ice Flow?
The force driving flow of glaciers is gravity.
•  Ice flows from places where the surface is high, to
places where the surface is low (like water in a stream.)
•  Speed of a glacier increases as the surface slope gets
steeper.
•  Speed of a glacier increases as the ice gets thicker.
•  Speed of a glacier increases as the ice gets warmer.
Dynamic Perspective and your Bank Account
Money managers can view investments from a
dynamic perspective too.
•  They talk about market forces and pressure on
the dollar .
•  Market forces control the rate at which money
flows into an investment account.
(e.g. through interest rates or bond returns).
•  Or the rate at which money accumulates or
disappears from a stock portfolio. ☺
Dynamic View: How Does Ice Flow Vary?
Speed of a glacier increases as the distance from the
bottom or from the valley wall increases
•  Drag or friction from the rock walls and bottom
Vertical
Section
Deformation
of a hole
drilled in a
glacier
Map
Deformation
of a line
across a
glacier
Longitudinal flow pattern in Accumulation area
Kinematic view
•  Flow tends to be faster closer to the Equilibrium Line,
because the amount of ice that must be transported (to
be equivalent to upstream snowfall) is greatest there.
Dynamic view
•  The glacier is thicker
at Equilibrium Line.
•  Thicker ice flows
faster.
Longitudinal flow pattern in ablation area
Kinematic view
•  Below the Equilibrium Line, the flow tends to slow down
because the ablation upstream has reduced the amount of
ice that is left to flow past each point each year.
•  The glacier terminates and nearly stops flowing when
there is no more ice left to melt.
Dynamic view
•  Glacier gets thinner
toward terminus
•  Thinner ice flows
more slowly.
Transverse flow pattern in Accumulation area
Kinematic view
•  Avalanches off valley walls pile up snow around edges.
•  Ice flows toward the center of the channel to carry away
high accumulation around the edges.
Dynamic view
•  Surface is highest
near edges.
•  Ice flows down hill,
toward valley center,
where surface is
lower.
Transverse flow pattern in ablation area
Kinematic view
•  Below the Equilibrium Line, melting can be enhanced
near dark valley walls.
•  Ice must flow toward the edges to replenish the
melting ice.
Dynamic view
•  Melting near margins
creates slope toward
margins.
•  Ice flows downhill,
toward margins.
Why understand glacier flow?
•  Big outlet glaciers flow to the ocean and break
off as icebergs. The rate that ice is lost depends
on the flow speed of those glaciers.
•  Ice cores tells a climate story. But the oldest ice
in a core may have come from far away. But
where, exactly?
•  Various things were lost on glaciers long ago.
Where should we look for them now?
January 15, 2011
But such bravado fades when talk shifts to what climbers are discovering
on Huayna Potosi's glacier: crumpled fuselage, decades-old pieces of
wings and propellers, and, in November, the frozen body of Rafael
Benjamin Pabon, a 27-year-old pilot whose Douglas DC-6 crashed into the
mountain's north face in 1990 …
Dynamics of Flow
•  Glacier with steep surface slope flows faster than a
comparable glacier with shallow slope.
•  A thick glacier flows faster than a comparable
glacier that is thinner.
Distinction between Flow and Deformation Rate
•  Deeper ice deforms faster (its shape changes faster)
•  Deeper ice also carries the ice above it along with it
•  Ice near the surface travels faster than deeper ice.
Vertical
Section
Deformation
of a hole
drilled in a
glacier.
demo: (like a deck of
cards on a slope.)
Brittle Behavior in Glaciers
Crevasses can form in the upper "skin" (about 30
meters, or 100 ft) of flowing glacier ice, when the ice
tries to stretch rapidly.
•  At greater depths, the ice
continually flows back in to
close up the cracks.
•  Crevasses almost always form
at right angles to the direction
of the maximum stretching.
Demo: silly putty
Hambrey and Alean, 2005. Glaciers.
HELP!COFFEE*
Hawley
Extremely
Lightweight
Portable !
Crevasse
Orientation
Freehand
Failure
Estimation
Equipment
[*Designed by former ESS 203 TA Bob Hawley]
Where Crevasses tend to Form
Crevasse on
Griesgletscher
Switzerland •  How might this crevasse
have formed?
Hambrey and Alean, 2005. Glaciers.
•  Since this is summer, you
can see it easily.
•  In winter it might be
hidden by a thin snow
bridge (falling through is
bad for your health!).
Crevasses on Fox Glacier, New Zealand
•  How did these crevasses form?
2006 ©Glaciers online · J. Alean · M. Hambrey
Crevasses on Arctic Piedmont Glaciers
•  Why did these crevasses form?
http://www.swisseduc.ch/glaciers/
Crevasses on an Antarctic Outlet Glacier
Ice accelerated into a valley through the Transantarctic
Mountains, then slowed down and spread sideways.
•  When did each
set of crevasses
form?
R.P. Sharp. 1988.
Living Ice
Flow
direction
The Curious Scientist
Questions on flow, deformation, and
crevasses…
Five-minute questions for your group …
•  Recorders please turn in reports at end of class.
1. Where are those Rocks Now?
You put a straight line of 5 stones across a
glacier in its accumulation area. They got
buried, and they will be carried along by the
ice. Eventually the ice encasing them will
melt in the ablation area.
•  One year after you laid them out, which of the stones was
closest to the terminus?
•  Which stone will probably reappear first at the surface in
the ablation area?
•  Which stone will go the deepest into the glacier before it
eventually starts to re-emerge?
•  Which stone will reappear closest to the terminus?
•  What will happen to the stones after they reappear at the
surface?
2. Crevasses on a Cascades Glacier
Crevasses tend to open up at right angles to the direction where
ice is stretched the most, i.e. like a rope of silly putty, the ice
tends to break clean across the direction in which you are
stretching it the most.
Suppose that you are climbing in the Cascades, and
you have been told to watch out for crevasses on
Glacier X near the equilibrium line.
0
1
2
3
•  Using the figure showing how a
line of stones across a glacier is
deformed by flow, suggest
which way the crevasses might
run near the glacier edge, and
why.
3. Alaskan Glaciers
•  Locate examples of all 3 types
of crevasses (transverse,
marginal, and splay) and
explain why they formed and
explain why they formed.
http://www.antarcticglaciers.org/modern-glaciers/structural-glaciology/splaying-crevasse/
3. Crevasses on
Saskatchewan Glacier
Google Earth
•  Locate
examples of
all 3 types of
crevasses
and explain
why they
formed.
4. Crevasses on
Saskatchewan Glacier
Google Earth
•  Locate examples of all 3 types of
crevasses (transverse, marginal,
and splay) and explain why they
formed.