THE DISEQUILBRIUM OF
NORTH CASCADE,
WASHINGTON GLACIERS
CIRMOUNT 2006, Mount Hood, OR
Mauri S. Pelto, North Cascade Glacier
Climate Project, Nichols College Dudley, MA
01571 peltoms@nichols.edu
NORTH CASCADE GLACIER
CLIMATE PROJECT 1983-2006
„
„
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„
„
Terminus behavior measured on 47
glaciers.
Annual balance measured on 10
glaciers.
Longitudinal Profile mapping on 14
glaciers.
Identification of the response of
glaciers to climate change
Monitoring changes in glacier runoff.
Glacier response to climate
change
„
Climate Change can cause variations
in both temperature and snowfall,
causing changes in mass balance.
„
A glacier with a sustained negative
balance is out of equilibrium and will
retreat to reestablish equilibrium.
„
A glacier with sustained positive
balance is also out of equilibrium, and
will advance to reestablish
equilibrium.
Equilibrium versus Disequilibrium
„
Glacier retreat results in the loss
of the low-elevation region of the
glacier. Since higher elevations
are cooler, the disappearance of
the lowest portion of the glacier
reduces overall ablation, thereby
increasing mass balance and
potentially reestablishing
equilibrium.
„
However, if the mass balance of
a significant portion of the
accumulation zone is negative, it
is in disequilibrium with the
climate and will melt away
without a climate change.
Evidence for Disequilibrium
„
The magnitude of the retreat of all 47
glaciers observed, resulting in the loss
of 5 out of 47 North Cascade glaciers.
„
Cumulative annual balance loss of 12.5 meters from 1984-2006, with
average glacier thickness of 40-75
meters.
„
Thinning in the accumulation zone
approximating thinning in the ablation
zone on Columbia, Colonial, Daniels,
Foss, Ice Worm, and Lower Curtis
Glacier.
Glacier Disequilibrium Identification
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The key symptom of a glacier in
disequilibrium is thinning along the
entire length of the glacier. Such as
on Foss Glacier below.
Accumulation zone of
Columbia Glacier, August 2005
„
Whereas a glacier retreating to a point
of equilibrium will thin predominantly
in the lower section of the glacier. For
example, Easton Glacier will likely
shrink to half its size, but at a slowing
rate of reduction, and stabilize at that
size, despite the warmer temperature,
over a few decades.
Why Measure Glacier Mass
Balance?
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Mass balance is the dominant control
of future terminus behavior.
Annual mass balance is the best
measure of annual climate and its
impact on a glacier and is viewed as
one of the most sensitive natural
recorders of climate
Annual balance is what we determine
on North Cascade glaciers. This is the
mean net change in glacier thickness
measured on a fixed date each year. It
is reported as an average value of
snow or ice lost in meters of water
equivalent gained or lost.
Lynch Glacier Mass Balance
Measurement Network:
Dots indicate accumulation measurement sites.
This is a high density of 200 pts/km2. The result
is excellent accuracy, mean densities in the
traditional methods is less than 20 pts/km2.
Crevasse Stratigraphic mass balance
measurements provides a two dimensional
view of snowpack thickness.
Crevasse Stratigraphy
„
Determined in vertically walled
crevasses the snow layer can be
traced from crevasse to crevasse and
can be corroborated with probing as
well. As a result the accuracy of this
method is higher than snowpits or
probing where only a point
measurement is obtained.
Probing
The annual balance records indicate the high
degree of correlation between nine North
Cascade glaciers including South Cascade
Glacier observed by the USGS
N o r t h C ascad e G lacier A nnual B alance
3
2
C o lumb ia
D aniels
1
F o ss
Ice W o r m
0
Lo wer C ur t is
Lynch
-1
R ainb o w
-2
Y aw ning
-3
East o n
So ut h C ascad e
-4
Year
Glacier Cumulative Annual
Balance: The negative trend has
increased.
North Cascade Glacier Cumulative Annual Balance
2
0
-2
-4
-6
-8
-10
-12
-14
Years
Terminus Behavior
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1880-1945: Rapid retreat of all glaciers.
1945-1975 period: Type 1 glaciers
advance; Type 2 glaciers approach
equilibrium; Type 3 glaciers continue
retreat.
1975-2004: Increasing retreat of all
North Cascade glaciers.
Disappearance of a significant number
of glaciers.
The differing response of the three
glacier types is due to the difference in
response time.
Glacier Type Characteristics
„ Type 1 have the highest mean elevations
(2200 m), largest mean slope (0.42, +0.07),
highest measured mean accumulation,
most extensive crevassing and highest
measured terminus region velocity (20 m/a,
+ 3 m/a ).
„ Type 2 glaciers have on average, a lower
slope (0.35, +0.08), a lower terminus region
velocity (7 m/a, +4 m/a), less crevassing,
and a lower mean accumulation rate than
Type 1 glaciers.
„ Type 3 glaciers have the lowest slopes
(0.23, +0.06), least crevassing, and lowest
mean terminus velocity (5 m/a, + 3 m/a).
Easton Glacier 1992: Type 1
Easton Glacier 2003:
300 m in 10 years.
A retreat of
Boulder Glacier Type 1 2003
Lower Curtis Glacier 1985 and
2003 Type 1: A vigorous glacier that
is still retreating ( 130 meters since 1987)
and thinning dramatically.
Lower Curtis Glacier 2006
Lynch Glacier 1978 Type 2:
Wide active front reaching Pea Soup
Lake, which it filled in 1976.
Lynch Glacier 1992 Type 2:
Narrow inactive front no longer in
contact with lake, has retreated 120 m
since 1984.
Columbia Glacier Type 2 1987
Columbia Glacier Type 2 2005:
The terminus is thick and retreat has
been 5 m/ year. However, thinning has
been dramatic.
Surface elevation change on
longitudinal profiles from three
glaciers.
Lower Curtis
Longitudinal Profile Elevation Change
Easton
Columbia
30
20
15
10
5
Distance from Terminus Benchmark
2 .6
2 .4
2 .2
2
1 .8
1 .6
1 .4
1 .2
1
0 .8
0 .6
0 .4
0 .2
0
0
e le v a tion c ha nge (m )
25
Columbia Glacier:
Changes in
longitudinal profile shows thinning from
terminus to glacier head indicating no safe
place to retreat to. This is common on many
Little Ice Age
North Cascade
glaciers.
Changes
in surface elevation on Columbia Glacier
1965
2002
1800
e le v a tio n (m )
1700
1600
1500
1400
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Distance (km)
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7
Whitechuck Glacier 1988-2005 (Post and
Scurlock). Type 3 glacier.
Whitechuck Glacier Type 3: The
former location of the north branch,
which retreated more than 1000
meters from 1985 to 2002.
Foss Glacier 1988 and 2005 Type 3
Causes of glacier mass loss has been
declining Winter Snowpack as noted on
April 1 at USDA Snotel sites. Since
precipitation has not declined this is a
result of rising temperature causing
winter melting and increased rainfall.
North Cascades April 1 SWE
2.50
1.50
April 1 SWE
Linear ( April 1 SWE)
1.00
y = -0.0069x + 1.4192
0.50
Year
2002
1998
1994
1990
1986
1982
1978
1974
1970
1966
1962
1958
1954
1950
0.00
1946
SWE (m)
2.00
Glacier mass loss is also due to rising
summer temperatures in the North
Cascades, as noted here for Diablo Dam
which is representative of the entire
range.
Ablation Season Temperature
19.00
18.00
16.00
Mean C
Linear (Mean C)
15.00
14.00
13.00
Year
02
20
98
19
94
90
19
86
19
82
19
78
19
74
19
19
70
19
66
19
62
19
58
54
19
50
19
19
46
12.00
19
Tem perature (C )
17.00
Ice Worm Glacier another case
of disequilibrium
Canadian Rockies have glaciers in
disequilibrium
Grinnell Glacier 1940 and 2005 in
disequilibrium
Conclusions
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All North Cascade glaciers have thinned
significantly since 1984.
The mean annual balance of -.41 m has led to an
average thinning of 9.5 m, 15-30% of the entire
glacier volume.
All North Cascade glaciers are retreating
significantly, and 5 of 47 monitored annually
have disappeared. Not much left of Ice Worm
Glacier below.
The result is less summer glacier runoff.