THE EFFECT OF DEBRIS ON GLACIER RESPONSE TO CLIMATE, ELIOT GLACIER,
GLACIER,
MOUNT HOOD, OREGON
KEITH M JACKSON; ANDREW G FOUNTAIN
Departments of Geography and Geology, Portland State University, Portland, Oregon, 97207
Introduction
Area and Length Changes
Ice Thickness
Much of the research concerning alpine glaciers has focused on “clean” glaciers largely devoid of rock
debris (Paterson, 1994). Consequently, little is known about the mass balance processes and effects of
climate change on debris-covered glaciers. However, debris-covered glaciers are relatively common on
the stratovolcanoes of the western United States (Nylen, 2005), in the Rocky Mountains (Konrad and
Humphrey, 2000), the Hindu Kush-Himalaya region of central Asia (Iwata et al., 2000), and the Andes of
South America (Corte, 1998). Our study examines the effect debris cover has had on the response of
Eliot Glacier to climate change as compared to the rest of Mount Hood.
Since 1901, the area of Eliot Glacier decreased from 2.03 ± 0.16 km2 to 1.60 ± 0.05 km2 in 2004 (-19%),
and the terminus retreated about 600 m over this time. During this 103-year period, glacier area
increased between 1956 and the early 1970s. The most pronounced shrinkage has occurred since
1995 with a loss of 0.14 km2 from 1995 to 2004. In comparison, the other six glaciers on Mount Hood
exhibit similar patterns, retreating through the first half of the 1900s, advancing or at least slowing their
retreat dramatically in the 1960s and 1970s, and then retreating again. Coe Glacier lost the least area,
15%, while White River Glacier lost the most, 61%. The seven glaciers examined lost 34% overall.
The A-profile, which once spanned the glacier, now spans the valley floor (possibly stagnant ice) 350 m
downvalley of the terminus. At the B-profile, an estimate of the glacier’s surface elevation in 1901 from
four H.F. Reid photographs suggests that the glacier was over 100 m thick. Current elevation is
approximately 52 m thick, which is about the same as in 1940. Climate variations at Mount Hood
resulted in a kinematic wave that traveled down the glacier arriving at the B-profile around 1960, causing
an increase in ice thicknesses of 40-50 m by the early 1980s. Since then, however, the ice has thinned
by 15-30 m at a rate of ~1.0 m a-1.
100
2.5
60
60
Eliot
Collier Glacier,
1910
Collier Glacier,
1994
75
Ladd
1.5
Wht Riv
New Clk
1
Reid
50
Sandy
0.5
0
Kiser
K.D. Lillquist
W.A. Langille
umbia
R iv e
Oregon
Eliot Glacier, flowing northeast
r
1925
1950 1975
Year
­
2000
00
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0.5
Mi d d le F o r k
t F or
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120
120
240
240 m
m
100
100 m
m contours
contours
2004
2004
Debris Supply
1907*
1907*
11 km
km
•
The field measurements of debris thicknesses (S), surface velocities (∇v), and melt rates ( b ) were
combined to estimate the rate of debris supply (∂S / ∂t ) to the surface of the glacier. This conceptual
framework for our study has been adapted from Lundstrom’s (1992), and we used Lundstrom’s
estimates of englacial volumetric concentration (C), porosity (Φ ), and subaerial deposition (D). Debris
supply from the glacier interior to the surface is about 4 – 6 mm a-1.
** 1901
1901 for
for Eliot
Eliot
88
Horizontal Strain Rate
•
∂S
bC
= − S∇ v −
+ D
(1 − Φ )
∂t
Measurements of melting show an inverse relationship with debris thickness. That is, ablation
decreases with increasing debris cover. Ablation rates decrease down-glacier and debris cover
thickens. These data are consistent with Lundstrom’s results. That melt (thinning) rates have only
increased slightly since measurement began in 1940 is most likely attributable to the insulation
properties of the debris cover.
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In 2001, PSU students measured the debris cover thickness throughout the ablation zone of the glacier.
Our measurements of debris thickness at each stake as well as other locations were combined with
previous measurements to create a comprehensive map of debris thickness across the ablation zone.
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km
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NEVADA
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Mt. Thielsen
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Benson Glacier,
1992
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Lateral
Lateral Margin
Margin
GPR
GPR Measurement
Measurement
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Stake
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Relative Value
Value (mm
(mm aa -1))
Relative
IDAHO
IDAHO
OREGON
OREGON
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H. Richardson
Three
Three Sisters/
Sisters/
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Broken Top
Top
Eliot Glacier, 2005
BB Profile
Profile
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Ice
Ice Thickness
Thickness (m)
(m)
90
High
90 ::90
High
90
60
60
30
30
Low
:0
0Low
0 :0
Coee
Co
Wallowa
Wallowa Mountains
Mountains
Mt.
Mt. Hood
Hood
Mt.
Mt. Jefferson
Jefferson
1907 Area
2004 Area
Terminus
2
Glacier
Loss (km ) Loss (%)
2
2
Retreat (m)
(km )
(km )
Coe
1.41 ± 0.13 1.20 ± 0.02
0.21
15
390
Eliot*
2.03 ± 0.16 1.64 ± 0.05
0.39
19
680
Ladd
1.07 ± 0.10 0.67 ± 0.05
0.40
37
1190
Newton Clark 2.06 ± 0.15 1.40 ± 0.14
0.66
32
310
Reid
0.79 ± 0.13 0.51 ± 0.05
0.28
35
490
Sandy
1.61 ± 0.17 0.96 ± 0.14
0.65
40
690
White River
1.04 ± 0.11 0.41 ± 0.03
0.63
61
510
Total
10.01 ± 0.95 6.79 ± 0.48
3.22
Average
1.43 ± 0.14 0.97 ± 0.07
0.46
34
609
ii
H.F. Reid
Benson Glacier,
1920
MODIS,
MODIS, 04.2004
04.2004
G
G
Pacif
Pa
cifiicc Ocean
Ocean
WASHINGTON
WASHINGTON
CC
A Look at Oregon’
Oregon’s Glaciers
Eliot Glacier, 1901
66
Debris
DebrisSupply
Supply Rate
Rate
Horizontal
Horizontal Strain
Strain
Debris
DebrisMelt-Out
Melt-Out
Downglacier
44
22
00
Debris supply rate
12-11
12-11 11-10
11-10 10-9
10-9
Debris melt-out
9-8
9-8
8-7
8-7
7-6
7-6
6-5
6-5
5-3
5-3
Stake
Stake Segment
Segment
Oregon
!!
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(
0.0
0.0
B-Profile
B-Profile
2004
2004 Terminus
Terminus
(
11 !
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22 !
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1A
!
(1A
(
2A
!
(
2A!
To provide a longer term perspective and a broader spatial
coverage, we made photogrammetric measurements of surface
boulders displacement between 1989 and 2004 using aerial
photographs from the U.S Forest Service.
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Total
Total
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Station
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5A
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An elevation profile established in 1940 (Dodge, 1964) was
resurveyed in 2005 to define the rate of glacier thinning. This
elevation profile was supplemented with a ground-penetrating radar
(GPR) survey of the debris-covered portion of the glacier to
determine current ice thicknesses (Fountain and Jacobel, 1997).
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55
Lundstrom
Lundstrom (1992)
(1992)
44
This
This Thesis
Thesis
33
22
11
00
10
10
20
20
30
30
40
40
50
50
Debris
Debris Thickness
Thickness (cm)
(cm)
!
(!
(
00
150
150
300
300 m
m
100
100
44
75
75
33
50
50
22
25
25
1975
1975
2000
2000
Year
Year
!
(
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(
!
(
(
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99
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10
10( !
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10C
10C 10D
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11
11
12
12
(
!
(
!
00
100
100
200
200 m
m
­
Area and length changes on seven of Mount Hood’s glaciers were
compiled in a geographic information system based on maps and
historic terrestrial and aerial photographs. These sources date
from 1901 to 2004. We calculated buffers around the glacier
perimeters to define the uncertainty in area. Root mean square
errors for georeferenced aerial photographs range from 3.6 to 9.6
m while buffers were defined at 20 m for ground-based
photographs and 15 m for oblique aerial photographs.
125
125
360
360
100
100
320
320
75
75
280
280
50
50
240
240
25
25
00
1900
1900
200
200
1925
1925
1950
1950
Year
Year
1975
1975
80
80
2000
2000
450
450
300
300
60
60
40
40
150
150
20
20
00
00
00
200
200
400
400
600
600
800
800
Distance
Distance Down-glacier
Down-glacier from
fromStake
Stake 12
12 (m)
(m)
Climate
11
1950
1950
70
70
De
Debris
bris Thickness
Thickness
Annual
Annual Ablation
Ablation
80
80
Despite the thickening of the debris layer, the glacier continues to thin; however, we
hypothesize that this thinning would be much more pronounced without the debris cover, and
that the debris cover is buffering the effects of warming temperatures. Because of this buffering effect,
Eliot Glacier appears to respond more sensitively to changes in winter mass input than to summer
temperatures (melting). It would be tempting to explain the relatively small shrinkage of Eliot and Coe
glaciers compared to other glaciers on Mount Hood solely in terms of a thickening of the debris layer.
However, other mitigating factors exist. Both Eliot and Coe have the highest accumulation zones which
head near the peak of Mount Hood (3425 m). Therefore, rising freezing levels and snow lines have not
affected these glaciers as much as the other glaciers, which have a smaller elevation range. This has
also been documented on Mount Rainier (Nylen, 2005).
References
55
1925
1925
60
60
100
100
­
125
125
00
1900
1900
66
00
!
(!
(
!
(!
(
Icee TThhick
icknnes
esss (m)
(m)
Ic
Control
Control Boulder
Boulder
A-Profile
A-Profile
!
(!
(
!
(!
(
Annual Ablation
Ablation (cm)
(cm)
Annual
Low
Low: :00
Stake
Stake
Survey
Survey Boulder
Boulder
1989
1989 Terminus
Terminus
1.5
1.5
High
High: :1.5
1.5
Fourteen PVC stakes were drilled into the debris-covered portion of
the glacier and surveyed to define displacement. Stake heights
were measured by hand to estimate melting. Seven boulders were
also surveyed. The surveys were completed with a total station
over a six-week study period in the summer of 2004 and once in
the summer of 2005.
Debris Thickness
Thickness (cm)
(cm)
Debris
Methods
600
600
120
120
77
umm
meerr AAbla
blation
tion (c
(cm
m dy
dy--11))
SSum
3423.6
13.4
!!
(
(
Stake
Stake
Measurement
Measurement
Site
Site
Debris
Debris Thickness
Thickness (m)
(m)
Annnuual
al TTeemp
mpeera
ratu
ture
re (( CC))
An
10 km
Eliot Glacier is a major
contributor to natural and
anthropogenic downstream
water uses.
!!
(
(
Debris Thickness
Agriculture
Rural Residential
Urban
Elevation (m)
5
!!
(
(
Conclusion
Photo: R. Schlichting
Land Use
Ice Thickness
Thickness (m)
(m)
Ice
0
Debriscovered ice
Glaciers
Hood River
Watershed
Eliot
Glacier
Winter Precipitation
Precipitation (cm
(cm
Winter
weq)
weq)
­
Mt. Hood +
1956 oblique photograph of
Eliot Glacier (Mazamas)
Average summer temperatures (five-year
running averages) have increased on Mount
Hood from 5.6 °C in 1902 to 8.8 °C in 2002
(Daly et al., 1997) whereas no overall trend
in winter precipitation is observed. From
1900 through 1940, temperatures warmed
and precipitation generally was low resulting
in glacier recession and thinning. In the
1950s to 1970s temperatures cooled and
precipitation increased resulting in glacier
advance and thickening. Since the middle
1970s air temperature increased and
precipitation decreased resulting in further
recession and thinning.
Corte, A.E. 1998. Rock glaciers, In: Williams, R.S., Jr., and Ferrigno, J.G., eds., Satellite image atlas of glaciers of the world: U.S. Geological Survey
Profesional Paper 1386-I (Glaciers of South America), 206 pp.
Daly, C., Taylor, G. and Gibson, W. 1997. The PRISM approach to mapping precipitation and temperature. 10th Conf. on Applied Climatology, Reno, NV,
American Meteorological Society.
Dodge, N.A. 1964. Recent measurements on the Eliot Glacier. Mazama, 47-49.
Fountain, A.G. and Jacobel, R.W. 1997. Advances in ice radar studies of a temperate alpine glacier, South Cascade Glacier, Washington, U.S.A. Journal of
Glaciology, 24:303-308.
Iwata, S., Aoki, T., Kadota, T., Seko, K., and Yamaguchi, S. 2000. Morphological evolution of the debris cover on Khumbu Glacier, Nepal, between 1978
and 1995. In: Debris-Covered Glaciers, IAHS Publication no. 264:3-11.
Konrad, S. K. and Humphrey, N.F. 2000. Steady-state flow model of debris-covered glaciers (rock glaciers). In: Debris-Covered Glaciers, IAHS Publication
no. 264:255-263.
Lundstrom, S.C. 1992. The budget and effect of superglacial debris on Eliot Glacier, Mt. Hood, Oregon. Ph.D. dissertation, University of Colorado, Boulder,
CO.
Matthes, F.E. and Phillips, K.N. 1943. Surface ablation and movement of the ice on Eliot Glacier. Mazama, 25(12):17-23.
Nylen, T.H. 2005. Spatial and temporal variations of glaciers on Mount Rainier between 1913 and 1994. M.S. thesis, Portland State University, Portland,
OR.
Paterson, W.S.B. 1994. The Physics of Glaciers. Oxford, United Kingdom: Pergamon Press.
Acknowledgments:
This work was supported by the Geological Society of America, Sigma Xi, the Mazamas Research Committee, NASA grant NNGO4GJ41G, NSF grant
BCS-0351004, the Crag Rats, Hassan Basagic, Mike Boeder, Heath Brackett, Gretchen Gebhardt, Frank Granshaw, Thomas Nylen, Oliver, Rickard
Pettersson, Rhonda Robb, Robert Schlichting, and Peter Sniffen.