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Susitna Joint Venture
Document Number
Please Return To
DOCUMENT CONTROL
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Susitna Hydroelectric Project
Supplemental Report
FERC Letter of 4/12/83
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SUSITNA 'HYDROELECTRI'C PROJECT
1-982
SUS!TNA BASIN GLACIER STUDIES
DECEMBER 1982
PREPARED BY: ~~
PREPARED FOR:
R&M QONSUL TAf+TS, INC.
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ALASKA POWER AUTHORiTY
SUSITNA HYDROELECTRIC PROJECT
TASK 3 -HYDROLOGY
1982 SUSITNA BASIN GLACIER STUDIES
DECEMBER 1982
Prepared for:
ACRES AMERICAN INCORPORATED
1000 Liberty Bank Building
Main at Court
Buffalo, New York 14202
Telephone: (716) 853-7523
Prep a red by:
Dr. William D. Harrison
Geophysical Institute
University of Alaska
Fairbanks, Alaska 997D1
R&M CONSULTANTS, INC.
5024 Cordo~a Street
Anchorage, Alaska 99502
Telephone: (907) 279-0483
, ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRiC PROJECT
1982 SUSITNA BASIN GLACIER STUDIES
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
ACKNOWLEDGEMENTS
INTRODUCTION
MASS BALANCE MEASUREMENT
GLACIER VELOCITY MEASUREMENTS
GLACIERS AND CLIMATE
REFERENCES
APPENDIX:
Abstract: Bowling S.A., Climatic Fluctuation and Water
Yield from Glacierized Basins in Alaska
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LIST OF TABLES
Number Title
1 Velocity Data for Susitna Basin Glaciers
LIST OF FIGURES
1
2a
2b
2c
2d
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1981-1982 Winter Balances of Susitna Basin Glaciers
Continuous Balance on Susitna Glacier at Three
Altitudes for 1981 Hydrologic Year
Continuous Balance on Susitna Glacier at Three
Altitudes for 1982 Hydrologic Year
Continuous Balance on West Fork Glacier at Three
Altitudes for 1981 Hydrologic Year
Continuous Balance on West fork Glacier at Three
Altitudes for 1982 Hydrologic Year
Surface Velpcity of Susitna Basin Glaciers
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AKNOWLEDGEMENTS •
Many peopl·a contributed to the glacier studies in the Susitna Basin in
1982. The field program was conducted by C. Schoch of R&M Consultants
and D. Johnson, R. Bergt, and S. Bergt of the Geophysical Institute,
University of Alaska. Data reduction was completeg by D. Johnson. The
report was compiled by Dr. W. D. Harrison and D. Johnson of the
Geophysical Institute, University of Alaska. The abstract on Qimatic
Fluctuations and Water Yield From Glacierized Basins an Alaska was
prepared by S.A. Bowling, University of Alaska. The work was
conducted under subcontract to R&M Consultants, Anchorage, Alaska.
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J Susitna Basin Glacier Studies -1982
I NTROOUCT I 0 N
The Susitna basin glacier studies program, conducted jointly by the
,,. University of Alaska and R & M Consultants, was continued in 1982. The
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previous studies are summarized by R & M and Harrison (1981). The studies
were carried out at a level sufficient to provide continuity in a modest
data collection program, but there has been little interpretation to date.
The glacier studies program was undertaken because of the significant
effect that glaciers have on runoff from glacierized basins. The importance
of the glaciers cannot be judged by the fraction of basin glacerized {4%
for Susitna above Gold Creek). There are several reasons. One is that
glaciers usually receive extremely high precipitation. It is known that
about 40% of the Susitna runoff comes from the mountain areas, so from
the point of view of the glaciers the rest of the basin is desert. A
second reason is that the Susitna glaciers, though they comprise a small
fraction of the basin area, have been wasting strongly enough to have
increased the stream flow appreciably at Gold Creek over the period of
the measurements upon which the hydropower potential estimates are based.
Failure to consider this factor of wasting glaciers in Europe has lead to
significant over-estimates of hydropower potential. A third factor is
that glaciers tend to have a beneficial regulating effect on runoff,
even in lightly glacierized basins such as that of the Columbia River.
It is likely that a good deal of the Susitna water produced in the dry
year of 1969 was from glacier ice melt. Although this effect is beneficial,
it is important to realize that the forecasting of seasonal release is
virtually impossible by ordinary procedures. This is important in
predicting minimum annual runoff, for example. A good summary of these
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ideas is given by Meier (1969) in a discussion of "Glaciers and Water
Supply".
MASS BALANCE MEASUREMENTS
The philosophy of the present glacier balance program is to obtain an
overview of how the Susitna basin glaciers compare with each other, and
with Gulkana Glacier, for which a relatively long balance record exists.
Insufficient data are being obtained to determine the net balances (the
net gain or loss of mass in a given year). We have measured winter
balance (a measure of the winter snow pack in the mountains), and continuous
balance at a few index sites. The measurements are in addition to the
generally lower altitude ones from the snow courses maintained by R & M,
and now span a time interval of two years. Techniques were similar to
those used last year (R & M and Harrison, 198l)c In particular, map
altitudes have been used; they are known to be seriously in error.
The \oJi nter ba 1 ance data are summarized in Figure 1 • A 1 though heavy
summer snowfall in 1981 made the definition of a late summer surface
tenuous, a 1981 summer surface of uncertain exact date but correlatable
from glacier to glacier was well defined. The data therefore give a good
intercomparison among glaciers, and a fair idea of the snow pack over the
summer 1981 to spring 1982 period.
Estimates of continuous balance at the index sites, where poles or
wires steam-drilled into the ice are maintained, are presented in Figures 2.
This convenient format is essentially that used by the U.S. Geological
Survey (Larry Mayo, private communication), and will permit easy comparison
with Gulkana Glacier data.
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I The extrapolation of these point measurements to give balances integrated
over each glacier or glacerized basin has not yet been doneo I,
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GLACIER VELOCITY MEASUREMENTS
Because most of the glaciers in the basin are thought to be subject
to surges (catastrophic advances of varying magnitude), and because it is
important to know how much ice fl~ws past their equilibrium lines, part
of the glacier studies program has been to obtain baseline data on glacier
flow regimes (seeR & M and Harrison, 1981). Seasonal velocity measurements
were therefore continued on West Fork, Susitna main branch, West Tributary,
and Turkey Glaciers, and initiated on East Fork Glacier. All measurements
were made near the equilibrium lines. The results to date are summarized
lij in Figure 3 and Table 1. The glaciers have a striking tendency to follow
the same seasonal velocity pattern.
IJ East Fork Glacier is of special interest because it is the-only one
~
1 studied so far concerning its contribution, from wasting, to the 1949-1980
I 11 . I: 1 runoff at Gold Creek. The possible effect of its dynamics (such as a
L
I: ~~ surge) on its surface geometry is therefore of spec L 1 interest. The
r average speed just below the equilibrium line over-the 1949-1980 interval
has been estimated from the 1949 and 1980 photo sets (Table 1). Since
this seems to be similar to the present speed, we suspect that no major
surge took place over that interval. A better interpretation awaits the
completion of the present seasonal velocity measurements on the glacier.
GLACIERS AND CLIMATE
·~s noted earlier, a possibly important factor is that glacier wasting
may have contributed significantly to the runoff at Gold Creek since
1949. Although we feel that the magnitude of the effect is still not
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well documented, it is of sufficient importance that we have tried to
address it further with the limited resources at hand. Accordingly, we
asked Dr. Sue Ann Bowling to present a paper at the 1982 Alaska Science
Conference that would introduce some of the climatological factors possibly
involved in a significant wasting of the glaciers, and their effects on
runoff. Her thoughts are sui11Tlarized by her abstract and the figures
that illustrated her talk (Appendix), which are presented with extended
fig~re captions.
Our very rough estimate of the contribution from glacier wasting to
runoff at Gold Creek between 1949 and 1980 is 13%. It indicates that the
very long tel'"'m estimates of water availability may be too high. What it
imp l i.es for the water supply on a shorter time seale, say several decades,
is less obvious, but several possible scenarios can be considered:
Scenario 1 (Figure 1, top line) - a climate warming gives a 13%
transient peak in the total runoff, which dies away as the glaciers shrink
to their new equilibrium sizes. If the transient persists for several
decades or more, the water decrease will be slow and will not affect the
short term economic viability of the project significantly. The problem
of estimating the transient response time is a famous one in glaciology;
it was realized to be important many years ago and is a hot subject in
current research, but it has not yet been solved. This means that the
response time cannot be calculated from present knowledge, although we
feel that it may be possible to put limits on it from a study of the
recent glacier history, and mass balance measurements.
Scenario 2 - a climate change puts an end to glacier wasting, and
the transient 13% of runoff is lost immediately {Figure 1A, top line,
followed by second line, for example).
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Some other possible scenarios are shown in Figures lA and 2A; there
are large uncertainties because what we know about the glaciers and the
climatology of the Susitna basin is insufficient to predict the runoff
response from a given change in climatic parameters.
What can experience elsewhere in the northern hemisphere till us?
Scenario 2 or perhaps scenario 1 with the transient coming to an end, has
been the experience in Swiss hydropower production in glacierized basins.
Whatever the scenario, the result has been a shortfall in expected water,
because of the failure to take into account the nature of the transient
contribution from glacier wasting. In the Grande Dixence project, the
largest in Switzerland, the shortfall after the project was operating at
near capacity in the mid-1960's was about 13% (Bezinge, 1978), about the
same as the nominal 13% from permanent ice loss estimated for Susitna
from g1acier wasting. The glaciers in Switzerland are relatively
stable now. It is uncertain how close a parallel Grande Dixence is to
Susitna. The former is an order of magnitude more glacierized, but the
glacier balances probably have been much more negative in the latter, and
the glaciers of Dixence are probably not surrounded by as relatively arid
terrain as those of Susitna.
The problem of water supply for hydroelectric use from glacier
wasting has also been recognized in North America. Tacoma, Washington
uses flow from the Nisqually River for a major hydro project. A program
, , of repeated mapping of the glacier to ascertain how much of the flow has
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been from permanent ice loss was begun by the public utility as far back
as 1930 (Meier, 1969) .
Of course the problem of the effect of a climate change on water
supply is a problem for unglacierized basins as well. But in the light
of the previous discussion there are differences, such as:
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(1) The water supply can change significantly even if there is a long
period of constant climate, and (2) the effects of glaciers can be in
addition to the better known ones. For example, a drop of both temperature
and precipitation might balance the glaciers, immediately cutting off the
13% from storage, which would be a loss in addition to that expected from
an unglacierized basin.
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REFERENCES
Bezinge, A., 1979. Grande Dixence et son hydrologie, La collection de
donnees hydrologiques de base en Suisse, Association suisse pour
1 •arnenagement des eaux. Service hydrologique national.
Meier, M. F., 1969. Glaciers and water supply. Journal of the American
Water Works Association. Vol. 61, No. 31, p. 8-12.
R & M Consultants, Inc., and W. D. Harrison, 1981. Alaska Power Author·ity
Susitna hydroelectric project; task 3 -hydrology; glacier studies,
Report for Acres American Inc., Buffalo, N.Y., 1 volume.
7
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TABLE 1 -VELOCITY DATA FOR SUSITNA BASIN GLACIERS
IT
Measurement Velocity r Glacier Interval Velocitx Azimuth
''
f' Susitna main 5-18-81 to 7-30-81 0.153 meters/day 304.2 grad
branch
7-30-81 to 9-2-81 0.115 296.2
. r:. 9-2-81 to 6-9-82 0.105 295.8
6-9-82 to 7-28-82 0 .. 240 295.6
J'. 7-31-82 to 9-1-82 0.117 297.6
r· ' Susitna Turkey 5-18-81 to 7-3-81 0.786 221.4
7-3-81 to 7-30-81 0.653 221.2 t ·. 7-30-81 to 9-2-81 0.530 222.0 --_;;-
J 9-2~·81 to 6-9-82 0 .. 612 224.8
6-9-82 to 7-31-82 0.847 229.6
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if 7-31-82 to 9-1-82 0.471 ~21.3
I Susitna West 5-30-81 to 7-3-81 0.373 247.7
Tributary
·' 7-3-81 to 7-30-81 0.321 247.1
I ! 't . 7-30-81 to 9-2-81 0.276 247.8
.I ~ 9-2-81 to 6-18-82 0.291 248.9
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6-18-82 to 7-28-82 0.481 251.7
I ! 7-31-82 to 9-1-82 0.307 251.2
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1 I : :. West Fork 5-17-81 to 7-30-81 0.227 2.91.9
'·' I 7-30-81 to 6-18-82 0.139 291.9 :
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6-18-82 to 7-27~82 0.289 293.4
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7-27-82 to 9-1-82 0.140 293.0
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I East Fork Aug-49 to Aug-80 0.23(7) i
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{~It 8-1-82 to 9-1-82 0.236 292.7
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ALTITUDE (meters)
1500
5000 6000
ALTITUDE (feet)
2000
LEGEND
A MACLAREN 5-21-82
D WEST FORK 5-23,24-82
6 SUSITNA 5-17-82
0 EAST FORK 5-18,20, 21-82
e TURKEY 5-15-82.
7000 eooo
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Figure 1: 1981-1982 winter balances of Susitna basin glaciers.
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9
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INTERNAL ACCUMULATION t-~o~CTT~~·NNnovv~· ~lomE~c~r-IJA&N~iriF~E~Bli~MuA~R-,~A~P~R~r-M~A~Y-.-.J~U~N-,~~JU~L~;=~A;U~G~~-S-EP--J_a
SUSITNA GlACIER 1981
, .
Figure 2a: Continuous balance on Susitna Glacier at three altitudes for 1981
hyd;ologic year.
10· \
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-.... c
: 80
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SUSITNA GLACIER 1982
Figure 2b: Ch· ontinou~ ·~let~ .ozt .Susi~.G.lac.ter at· i:J:lree altitudes fqr 1~82
~drolog29 y~ . ·
----=-------._~m--~~·••~~~·•n•••-•~••~-~~a~n~.-A"'•--~~~a•.a•u••• .. ._,.__.._ ...... ---------·-------------------
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t~~~.,r-~~·~.~~·,•·t-~~~-r--~~-,--~~~--~~--r-~~--r-~~~,-~~~,IN_T_E_R~N~A~l~A~C~C:U:M;U;l~AT~t:O~N~----~
OCT NOV DEC _ JAN fEB MAR APR MAY JUN JUL AUG SEP -G
WEST FORK GLACIER 1981
Figure 2c: Continuous balance on West Fork Glacier at three altitudes for
1981 hydrologi~ year.
12
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OCT NOV DEC
Figure
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l:~ JUL AUG
INTERNAL ACCUMULATION
JAN FEB MAR APR MAY JUN .1 JUL . I AUG I . SEP . -a
WEST FORK GlACIER 1982 . .
2d: Continuous balance on West Fork Glac~er at three altitudes for
1982 hydrologic year.
13
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!"---, Figure 3: Seasonal behavior of the horizontal
f-, . I component of the surface velocity
• • . I of the Susitna basin glaciers, in
I all cases near their equilibrium
..___ SUSITNA TURKEY TRIBUTARY I lines. Average velocity between
I survey dates is given. The dashed _ -
I lines in the Turkey data imply that . errors exist due to advection of I
L--t the matker stake into a· steeper
reach of the glacier. Stakes were
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SUSITNA W. TRIBUTARY . '
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I I SUSITNA MAIN BRANCH . .
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STAKES MOVED t I J I I I I I I -.... .... --.... .... -1--N >->-1-N M >-> 00 OJ a: > ClO co _, a. 0 m m <( <( _, a. . 0 0) m
::> w z --:E ::! ::> w z .... .... .., en ..., tl) .
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APPENDIX
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ABSTRACT
Climatic Fluctuations and Watt~r Yield from
Glacerized Basins in Alaska=
S. A. Bowling (Geophysical Institute, University
of Alaska, Fairbanks, AK 99701)
Runoff from glacierized basins is strongly
influenced by water stored in glaciers. In
the part of the Susitna basin proposed for
hydropower development, for instance, which
is 4% glacierized, it is possible that roughly
13% of the runoff s1nce stream gaging began
has been coming out of storage in the glaciers.
The climatic response of the glaciers, and thus
of long-term and short-term runoff, are of
considerable interest.
Precipitation and glacier ablation in Alaska are
not unconnected. The major source of both heat
and moisture is the Pacific Ocean. An increase
in transported Pacific air into the basin would
increase precipitation and ablation at higher
elevations, and probably increase the runoff
substantially, even if the glaciers began to
grow again. On the other hand, more Arctic air
would reduce both precipitation and ablation at
all elevations. Major changes in total runoff
are thus possible.
16
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Figure lA
Conceptual models of glacier response to a step change in temperature
alone or preci pi tat ion a 1 one. The basic assumptions are:
1) Most precipitation is in the form of snow.
2) The glacier response after the step change is of the form
A(t) =A' + (A 0 -A')e-t/T , where A(t) is the glacier area
at time t, A0 is the initial glacier area (assumed to be in
equilibrium with the initial temperature and precipitation), A'
is the glacier area in equilibrium with the new temperature
and precipitation, and T is the time constant for glacier
response.
3) The initial change in glacier runoff is due to changes in ablation
(for temperature change) or precipitation on the glacier which
does not go into storage in the glacier (for precipitation
change). The steady state glacier runoff is assumed proportional
to the steady state area of the glacier times the final
precipitation.
4) Change in runoff from the glacier-free area is complex. A rise
in temperature will cause an immediate drop in runoff due to
increased evapotranspiration, and vegetative changes could
result in delayed changes in evapotranspiration as well,. The
longer term rise in runoff is due to the increase in area as
the glaciers shrink. In a watershed where a large part of the
runoff is concentrated during the spring snowmelt, evapotranspirtation
is expected to have a relatively minor effect, as shown here.
In other cases its effects could approach or even exceed the
runoff effect.
18
r II
I I I I
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II
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a
a
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a E TT '"'lil"• .,.,.., zr 1,. • t ;nwtwr n r urrsr?Z · m z· I
Changes in runoff due to changes in precipitation are simpler.
Added precipitation shows up initially as a direct increase in runoff.
Partitioning between glacier and non-glacier runoff changes as the relative
areas change. The difference between the observed total runoff and the·
precipitation change over the basin is due to water storc.:ge (or release
from storage) in the glacier.
To summarize, the effect of a temperature change is a short term
spike in the opposite sense to the long term change in the total runoff.
The effect of glacierization on a precipitation change is to delay and
initially weaken the runoff change. The time scale (T) for glacier
adjustment would vary with the basin and the magnitude of the change,
but would probably be years to tens of years for small basins and tens
to hundreds of years for larger ones.
19
1 ' '
' • .:.~~··.. ~ ~ ' ;~ >
CLIMATE
T ___...I
p I
T--~
p ____,I
T __..I
p I
T ---~
p-1
..
GLACIER.
AREA
-----.
/
/
• a • • • •• . . . . . . . . ..
-........ ---
/ /-
.. . . • . ···~~~ .. ............
)
GLACIER
RUNOFF
. .,........ -----'· ,... : .......
• • • • •
· .. 4~jl\W·
11~1/. ............ ..
v
20
-~-~------~~-· ----·-----...... l ll:31E31DI---·
RUNOFF FROM'
NON-GLACIERIZED
AREA
..
•••••• ••••••••••• ...
. ______ I -
TOTAL
RUNOFF
=·· . "'• . . . •......::-..... -----
• ~flllll""" ••o••o••••••• :.---
0 •
•
I
.. ____ ...._,_ .. . ----~· • • •• • • •• •o• • • • • v .......
'·
r--------:-------------------------------
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Figure 2A
The results of combining the effects of temperature and precipitation
from Figure 1. Two responses are shown for cases in which the sign cannot
be predicted a priori. The ambiguities her~ are much greater~ but
climatological data do allow some inferences:
1) The major moisture-bearing winds in Alaska come from the Gulf
of Alaska and are also quite warm. The orientations of both
the coast complex and the Alaska Range are such that these
winds can result in heavy orographic precipitation with a
positive correlation between temperature and precipitation~
Thus the two upper rows of scenarios are the most likely for
these areas. An inverse correlation is possible for areas
sheltered from southerly flow and is in fact observed for
Fairbanks.
2) Temperature and precipitation in mountainous areas of Alaska did
increase around 1976, and Mayo and Trabant (1982) have
demonstrated that at least one Coast Range glacier responded to
the change with an increase in annua 1 ba 1 ance. Alaska Range
glaciers seem as yet to have shown little response, so it is as
yet uncertain which of the two glacier area curves shown for each
of the two upper rows of the figure would apply in the Alaska
Range.
3) At least the East Fork glacier has been thinning markedly in
recent years, but the climatic regime responsible cannot be
identified as there is no evidence as to when the thinning
started. The Glacier m~y well last have been in equilibrium
sometime in the 18th or 19th century. Further study is needed
21
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lJ
IJ
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0
0
0
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REFERENCE
on the correlation of climate with glijcier balance in the
Susitna area and on the dating of their last period of extension.
Mayo, L. R. and D. C. Trabant, 1982. Observed and predicted effects
of climate change on Wolverine Glacier, Southern Alaska. Proceedings
of the conference, The potential effects of carbon dioxide induced
climate change in Alaska, in press.
22
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