The Nines Creek Ice and Rock Avalanche: an Example of the Impact of Climate Change on Catastrophic Geomorphic Processes in the Kluane Ranges, Yukon Territory, Canada
P.S. Lipovsky1, C.A.Huscroft2 and A.G. Lewkowicz3
1 Yukon Geological Survey, Whitehorse, YT
2 University College of the Cariboo, Kamloops, BC
3 University of Ottawa, Ottawa, ON
Bedrock consists mainly of highly deformed Paleozoic to Early Mesozoic and
Permo-Triassic volcanic and sedimentary rocks intruded by Paleozoic and Late
Jurassic to Tertiary plutons and dykes (Dodds and Campbell, 1992).
The study area generally experiences a sub-arctic continental climate with long cold
winters, short mild summers, low relative humidity, and low to moderate precipitation.
'W
°51
13 8
85
00
138
61°
9' N
Yukon
Nines Creek
Northwest
Territories
Whitehorse
8000
75 0
60ºN
Alberta
e
USA
VALLEY GLACIER
SEGMENT
DESCRIPTION OF FAILURE
LEGEND
In total, the Nines Creek avalanche travelled a maximum distance of 1.8 km
(H/L= 0.31). The travel path of the failure can be divided into three sections which
are described below: the upper precipice, the valley glacier segment, and the glacier
forefield runout area (Fig. 4).
boulder >1 m
#
ice cast
!
debris hummock
plough mark orientation
Neoglacial (?) moraine
6 1 °1
CAUSE OF FAILURE
0' N
1947
1972
2004 (estimated)
Descriptions of the glacier terminus by witnesses (pers. comm. Cameron Bell,
2004), as well as analysis of historical aerial photography, suggest that the Nines
Creek avalanche can be attributed to the calving of a hanging glacier (Fig. 2).
Below the precipice, the ice fragments and rock debris travelled 1100 m over a
valley glacier to a 165 m wide constriction in the valley bottom. This zone has an
average slope of 15º. Air photographs illustrate that the glacier was debris-covered
prior to the failure (see Fig. 4). On the valley glacier, the deposits of the avalanche
are difficult to distinguish from morainal debris. Glacial movement since the failure
is inferred to have disturbed the original character of the avalanche debris.
GLACIER FOREFIELD SEGMENT
Beyond the valley glacier, the debris extends in the form of two lobes over a 600 x
300 m area (Fig. 8). This area consists of a smooth and semi-vegetated outwash
plain with an average slope of 10 degrees. Witnesses visiting the failure site
observed “large chunks of glacier” within this area a week after an earthquake
shook the vicinity in July of 1995.
Within the glacier fore field, the avalanche deposit consists of a discontinuous layer
of angular rubble composed of basalt and basaltic breccia. Distinguishing features
of the deposit include:
Its thin, discontinuous nature (average thickness of <30 cm), allowing
pre-existing fluvial features to show through it (Fig. 6).
The general paucity of matrix material.
The source zone for the ice is clearly delimited on aerial photos from 1999 and has
a footprint of 33 000 m2 (Fig. 4). The height of the ice cliff in the same 1999 photos,
was 46 ± 4 m, four years after the event. Photogrametric measurements of changes
in glacier geometry suggest that 590 ± 50 *103 m3 of ice was involved in the
failure.
"
"
surveyed
estimated
"
"
"
"" " "
"" """
"
" "
"
"
""
""
"
"" "
""
"
extent of deposit
5500
VALLEY GLACIER SEGMENT
"
edge of glacier tongue
'W
Witnesses observed an “impressive blue cliff of ice” above the precipice, a week
after an earthquake shook the local area (pers. comm. Cameron Bell, 2004).
6000
138
°52
Upon detachment, the collapsed ice mass dropped 200 m over a near-vertical basalt
cliff, entraining massive blocks of bedrock in the process. Assuming free-fall of a
500 000 ton (approximate) mass of ice, the debris would have attained a speed of
63 m/s once it hit the base of the cliff.
source area for ice collapse
'W
UPPER PRECIPICE
Figure 3. View looking northwest from above hanging glacier looking down the 1.8 km
runout of the rock and ice avalanche. Debris-covered valley glacier and glacier forefield
in background.
valley constriction
GLACIER FOREFIELD
SEGMENT
Figure 1. Location of Nines Creek
rock and ice avalanche.
Figure 2. View looking east at hanging glacier. Red line
outlines upper limit of the ice mass which collapsed in
1995 (see Fig. 4)
Nines Creek
0
200
Elevations in feet
Contour interval 100 ft
400 m
W
120ºW
61°
9' N
700
0
130ºW
50ºN
138
°51
140ºW
1000 km
°53
'
Vancouver
500
750
0
138
British
Columbia
UPPER
PRECIPICE
CANADA
Pacific Ocean
0
0
!! !
The Nines Creek Rock avalanche is located (Fig. 1) in the Kluane Ranges, which are
a narrow band of steep, rugged and glaciated peaks extending up to 2500 m above
sea level. The Kluane Ranges separate the large icefields of the Saint Elias
Mountains from the interior plateaus of the Yukon Territory.
70ºN
Fairbanks
#
REGIONAL SETTING
USA
!!!
!
!!!
!
!!!!
!
!
!
The results of this study distinguish the deposit from other types of debris accumulations, and highlight a rarely documented climate change related glacier hazard
with potential to damage infrastructure in the northern Cordillera.
N
6500
The event was likely seismically triggered by a M 5.2 earthquake that occurred in
June 1995, during the same week as the failure. Repeated aerial photography of the
site, however, indicates that glacial recession and thinning had taken place for at
least five decades prior to the failure and is likely an important pre-condition for the
initial ice collapse.
Alaska
70
00
#
Calving of a hanging glacier initiated the avalanche. A portion of the glacier
detached and dropped down a 200 m high near-vertical basalt cliff, entraining
massive blocks of bedrock in the process. Below the cliff, the ice fragments and
rock debris travelled 1100 m over a valley glacier to a 165 m wide constriction in
the valley bottom. The mass then travelled up to 600 m further, spreading out over
the low-angled glacier fore-field with an average slope of 10 degrees. The deposit
covers an area totalling 0.4 km2.
Arctic Ocean
"
Detailed field investigations of an exceptionally large ice and rock avalanche
deposit were undertaken to characterise the cause, behaviour, and impacts of the
failure. Distinguishing features of the deposit include a general paucity of matrix
material, a high concentration of large boulders along the periphery and at the toe of
the deposit, and virtually ubiquitous perched clasts and boulders. The failure had an
exceptionally long runout distance (H/L= 0.31), transporting several boulders larger
than 50 m3 a distance of up to 1.8 km. The largest intact boulder at the toe of the
fan was 250 m3. Plough marks made by boulders and large ice blocks that have
since melted are traceable for nearly 40 m in aerial photographs. Arcuate push
ridges, developed in the terminal zone, show evidence of both shearing and folding
of the pre-existing soil.
°50
'W
ABSTRACT
Energy, Mines and Resources
Figure 4. Topographic map underlain by 1972 aerial photograph (A23000-124)
depicting historical glacier positions and various debris characteristics.
Figure 5. Photograph of delicately perched cobble on
pebbles suggesting that the deposit had a matrix of comminuted ice that melted after the failure came to rest.
TRAVEL MECHANISM
Several lines of evidence suggest that the long runout distance of the Nines Creek
rock and ice avalanche was facilitated by a slushy matrix of comminuted ice.
The slushy matrix would have melted by the time witnesses first visited the site, a
week after the failure (pers. comm. Scott Casselman, 2004).
The number of large boulders and the thickness of the debris are greatest
near the periphery of the deposit (Fig. 4). These features are characteristic of
debris-laden slush flows in northern Sweden (Rapp, 1959).
Locally well-preserved vegetation beneath the failure’s thin mantle of rubble is
also a characteristic shared by slush flows, (Matthews and McCarroll, 1994;
Gardner, 1983).
Perched boulders and cobbles are common near the periphery of the debris lobes
(Jomelli and Francou, 2000, Lewkowicz and Hartshorn, 1998).
Very little moisture is thought to have been entrained along the travel path since
the glacier was already debris-covered and the basin was mostly snow-free at
the time of the failure.
Three features argue against the alternative hypothesis of air entrainment:
Seismic shaking and glacial thinning are both considered factors that contributed to
the failure:
The long plough marks made by boulders and large ice fragments imply
laminar flow and do not suggest the turbulence required for air entrainment.
SEISMIC SHAKING
Visits by exploration geologists to the upper basin of Nines Creek isolate the
failure event to a single week in June of 1995. During that same week, exploration geologists camped 20 kilometers from the failure felt ground-shaking associated with a M5.2 earthquake recorded by the Haines Junction seismic station
on June 12.
The previously competent debris forming the steep-sided hummocks (Fig. 9)
observed in the forefield area would likely not have survived collisions
involved in air entrainment.
Air entrainment could not have produced the delicately positioned clasts
perched upon each other in the glacier forefield (Fig. 5).
GLACIAL THINNING
The Kluane Ranges comprise an area of high seismicity and the study area has
historically experienced similar, and even more intense, episodes of shaking
than the earthquake that is linked to the failure. However, earlier seismic events
did not initiate glacier collapse. Therefore, a unique precondition must have
existed.
IMPLICATIONS
Long-term glacier thinning caused by climate change likely played a significant
pre-conditioning role in this landslide.
Repeated aerial photography of the site indicates that glacial recession and thinning had taken place for at least five decades prior to the failure (Fig. 4).
Weakening of the ice mass by thinning is inferred to have contributed to the ice
collapse.
A high concentration of large boulders (volumes up to 250 m3) along the
periphery and at the toe of the deposit (Fig. 4 & 9).
If climate warming continues, similar catastrophic failures of glacial ice and rock
with long runout distances could increase in frequency. These types of failures have
rarely been documented as a potential hazard in North America.
Figure 10. Push ridge in front of large boulder, which travelled in direction of arrow.
Dissection of the push ridge showed evidence of both shearing and folding of the
pre-existing soil.
Ubiquitous perched clasts and boulders, even on the tallest transported blocks
(Fig. 5 & 7).
Numerous steep-sided hummocks of debris surrounded by smooth rings of
additional debris (Fig. 7).
The recognition of this type of failure mechanism and the characteristics of the
deposits it leaves behind may have implications for hazard analysis in other steep
and glaciated areas, particularly transportation corridors and recreational areas in
the Canadian and American Rocky Mountains.
ACKNOWLEDGEMENTS
The authors would like to kindly acknowledge funding from the Knowledge and Innovation fund and NSERC. Cameron Bell and
Scott Casselman of Inco Ltd. are sincerely thanked for their patience with our questions concerning the events of 1995. The authors
are also indebted to Steve Israel and the Yukon Geological Survey for helicopter support.
Long (30 m) plough marks (Fig. 9) leading to boulders with push ridges
(Fig. 10) and empty push ridges (ice casts) (Fig. 11).
REFERENCES
Two distinct trajectories of debris are suggested by the orientation of plough
marks and the orientation of debris lobes (Fig. 4 & 9).
Dodds, C. J. and Campbell, R. B., 1992. Geology, SW Kluane Lake map area 115G & F E1/2 , Yukon Territory. Geological Survey of
Canada, Open File 2188, 1:250,000 scale.
Gardner, J. S., 1983. Observations on erosion by wet snow avalanches, Mount Rae area, Alberta, Canada. Arctic and Alpine Research,
vol. 15, no. p. 271-274.
Gordey, S.P. and Makepeace, A.J. (comp.), 2003. Yukon digital geology, version 2.0. Geological Survey of Canada, Open File 1749,
and Yukon Geological Survey, Open File 2003-9(D), 2 CD-ROMs.
Jomelli, V. and Francou, B., 2000. Comparing the characteristics of rockfall talus and snow avalanche landforms in an Alpine
environment using a new methodological approach: Massif des Ecrins, French Alps. Geomorphology, vol. 23, no. p. 181-192.
Lewkowicz, A.G. and Hartshorn, J., 1998. Terrestrial record of rapid mass movements in the Sawtooth Range, Ellesmere Island, NT,
Canada. Canadian Journal of Earth Sciences, 35(1), p. 55-64.
Matthews, J. A. and McCarroll, 1994. Snow-avalanche impact landforms in Breheimen, Southern Norway: Origin, Age, and
paleoclimatic implications. Arctic and Alpine Research, vol. 26, p. 103-115.
Rapp, A., 1959. Avalanche boulder tongues in Lappland descriptions of little-known forms of periglacial debris accumulation.
Geografiska Annaler., vol. XXXXI, no. 1, p. 34-48.
Figure 8. Oblique aerial photograph of glacier forefield
depicting large boulders and hummocks which outline two
distinct lobes of debris.
Figure 6. Oblique aerial photograph of Nines Creek rock and ice avalanche depicting the
source area, upper precipice, valley glacier segment and glacier forefield segment.
CONTACT INFORMATION
Panya S. Lipovsky, Yukon Geological Survey, 2099 2nd Avenue, Whitehorse, Yukon, Y1A 1B5
[email protected], tel. (867) 667-8520
Indian and Northern Affaires indiennes
Affairs Canada
et du Nord Canada
Knowledge & Innovation Fund
Figure 7. View looking up valley of large boulder entrained
in the failure. Note perched clasts on top of the boulder.
Location of boulder shown by white arrow in Fig. 6.
Figure 9. Photograph of debris hummocks inferred to be
the thawed remnants of large fragments of frozen till;
looking up valley to source area.
Crystal A. Huscroft, Department of Geography, University College of the Cariboo, Box 3010, 900 McGill Rd.,Kamloops, BC,
V2C 5N3, [email protected], tel. (250) 377-6132
Figure 11. Push ridge and corresponding ice cast formed
by lodgement of a large fragment of glacial ice (in the
direction of the arrow) at the time of failure.
Antoni G. Lewkowicz, Department of Geography, University of Ottawa, Ottawa, Ontario, K1N 6N5, [email protected]
C13B-0281