measuring avalanche frequency on the balu pass trail

Measuring Avalanche Frequency on the Balu Pass Trail, Glacier National Park, BC

Geog 477 – Fall 2011

Allison Dick, Donald McFarlane, and Robyn McGregor

Objective

• Obtain dendrochronoligical reconstructions of avalanche activity

• Use avalanche reconstruction in conjunction with snowpack data to determine avalanche frequency – may be used as a predictive measure to aid in mitigating avalanche related injuries or deaths

Table of Contents

• Site Description

• Avalanche Characteristics

• Slab Avalanches

• Data Collection

• Lab Analysis

• Results

• Discussion

• References

Site Description

• Trail head located near the parking lot of Rogers Pass Discovery Center

• Balu Pass Trail - 6.4 km length

• Avalanche track/study site - approx. 3.8 km from trail head

Area Map and Study Site

Site Description Cont. • The Balu Pass Trail receives a

great deal of avalanche activity every year

• Just about every avalanche track intersects with the trail

• Lack of information regarding frequency of avalanches on specific tracks

• Bruins Pass = popular backcountry skiing area

• Balu Pass Trail is classified as an area of complex terrain

• Understanding the frequency of high magnitude avalanches for individual slopes can be highly beneficial for backcountry skiers when making route and traveling decisions.

Avalanche Research Team!

Avalanche Characteristics

• Slab avalanches of high concern

• Formed by weak layer within snow profile

• Often result of surface hoar, rain on snow, or increased solar radiation on snow – freezes and creates shearing point

• Snow accumulates above weak layer until failure is reached

http://climbmountains.wordpress.com/category/winter/winter-climbing/page/2/

• Surface Hoar:

– Develops when the air above a snow layer becomes supersaturated and condenses on snow surface – freezes and becomes layer of icy snow that may act as a weak layer within the snow profile

– Weak Layer is the shearing point for slab avalanches

• Rain Crusts

o Can occur when temperature increases temporarily, enough for precipitation to fall as rain. As temperatures once again fall, the wet surface layer freezes, resulting in a weak layer.

• Sun Crusts

o Occur when slopes receive an increase in solar radiation

o Surface snow melts and freezes over night o New snow accumulates overtop of unstable

weak layer

• Occur on slopes ranging from 25 – 45 degrees

• Dangerous to area users, such as back country skiers

Slab Avalanches

• Much like the 2003 Tragedy along the Balu Pass Trail

http://www.colorado.edu/geography/class_homepages/geog_3251_sum08/

• 17 students caught in Balu Valley avalanche while on school trip

• 7 did not survive

• Raised many questions about avalanche safety and awareness standards for backcountry winter recreation

• Data regarding avalanche frequency may be useful in preventing further tragedies

Data Collection

• Aim was to create an avalanche reconstruction using dendrochronoligcal techniques

• Sub Alpine Fir was sampled systematically to represent extent of avalanche track

• Increment borer used to obtain tree cores

• Hand saw used to obtain tree discs

Locations of Obtained Samples

Avalanche Evidence

Up Hill Scarring Up Hill Stripped Off

Hand Saw and Increment Borer

Tree Coring and Cookie Cutting

• Cores were taken at chest height

• Cookies were cut close to the base of the tree

Reaction Wood

• Forms when force of avalanche results in bending of tree

• Tree diverts energy to regain upright position

• Shown as characteristic stress markings in tree ring pattern:

Scars

• Scars found on bark of trees

• Occur when debris is dragged along tree bark, leaving a wound

• By backdating from Scar to pith and determining total age, a year of scarring event can be determined

Scar Samples

Lab Analysis • Cores and Discs taken to lab • Sanded and mounted for viewing under

microscope • Tree age determined by counting rings inward

from bark to pith • Years with reaction wood (darker, wider rings)

recorded • Event years compared to snowpack data to

determine presence or absence of relationship

Mt. Abbot and Glacier Weather Stations with

Respect to our Study Area

Study Area

Results

• Resulted in 111 years of usable data

• 150 events of scars or reaction wood recorded

• Given an error of +/- one year, a graph of avalanche events could be compiled

Tree Ages

0

50

100

150

200

250

300

350

R2 R3 R7 R1a R1b error1 R6 R4 R9 R8 Error C1 C2 C2#2 C2b C2b-b C3 C4a C4b C4a#2 C5 C6 C7

Age

(ye

ars)

Field Samples from lowest altitude to highest altitude

Age of Tree Core and Ring Samples from Avalanche Site, Balu Trail, Roger's Pass, BC

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0

50

100

150

200

250

300

350

1959

1960

1961

1962

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

Nu

mb

er

of

Re

ac

tio

n W

oo

d a

nd

Sc

ars

Sn

ow

De

pth

(c

m)

Year

Relationship Between Average Annual Snow Depths and Reaction

Wood / Scars Found in Each Year Along the Balu Trail, Roger's Pass,

BC, 2011

Number of reaction wood and scars

Average Snow Depth from Mt Abbot and Glacier weather stations

2 per. Mov. Avg. (Number of reaction wood and scars)

Order of Events

YEAR Number of Reaction wood and Scars within the year

Major or Minor Events

Time between previous event (years)

Time between Moderate to Major events (years)

1 1906 3 Minor 0 - 2 1939 3 Minor 33 - 3 1968 3 Minor 29 - 4 1971 4 Moderate to Major 3 0 5 1974 3 Minor 3 - 6 1976 3 Minor 2 - 7 1979 3 Minor 3 - 8 1984 4 Moderate to Major 5 13 9 1988 4 Moderate to Major 4 4

10 1989 5 Major 1 1 11 1993 3 Minor 4 - 12 1998 3 Minor 5 - 13 1999 4 Moderate to Major 1 10 14 2000 3 Minor 1 - 15 2004 3 Minor 4 -

Major, Moderate, and Minor Events

Occurring from 1900-2011

Discussion

• Tree ring data did not yield a definitive trend of avalanche data

• However, comparisons with snowpack data could provide insight into the relationship between snowpack and avalanche frequency

• More research would be required to determine a definitive predictive method for avalanche frequency using dendrochronology and snowpack reports

References Content: Canadian Avalanche Centre. (2011). Online Avalanche Course. Retrieved November 5, 2011, from Canadian Avalanche Centre: http://www.avalanche.ca/cac/training/online-course Canadian Broadcasting Corporation. (2003, February 4). Teens were Caught in Powerful, Fast-Moving Avalanche. Retrieved November 05, 2011, from CBC: http://www.cbc.ca/news/canada/story/2003/02/02/revelstoke030201.html Jamieson, B. (2004). Between a Slab and a Hard Layer. Avalanche News , 70. Jenkins, M. J., & Hebertson, E. G. (2004). Using Vegetative Analysis to Determine the Extent and Frequency of Avalanches in Little Cottonwood Canyon, Utah. Department of Forest Resources,. Logan, Utah: Utah State University. Johnston, K. S., & Jamieson, B. (2011). Estimating Extreme Snow Avalanche Runout for the Columbia Mountains, British Columbia, Canada. Department of Geoscience. Calgary, Alberta: University of Calgary. Stoffel, M., Bollschweiler, M., Butler, D. R., & Luckman, B. H. (2010). Tree Rings and Natural Hazards. Springer Science and Business Media. Water Stewardship Division: Ministry of Environment (nd). Historic Snow Survey Data for British Columbia, 1959 – 2011. Stn 2A02 [Data File]. Retrieved from http://a100.gov.bc.ca/hub/mss/stationdata.do?station=2A02 Water Stewardship Division: Ministry of Environment (nd). Historic Snow Survey Data for British Columbia, 1959 – 2011. Stn 2A14 [Data File]. Retrieved from http://a100.gov.bc.ca/hub/mss/stationdata.do?station=2A14

References, Con’t Images: Google Earth (2011) Mountain Climber’s (2010) Retrieved November 24 from http://climbmountains.wordpress.com/category/winter/ winter-climbing/page/2/ Parks Canada (2011). Glacier National Park. Avalanche Terrain Ratings. Retrieved November 24.2011 from http:/ www.pc.gc.ca/eng/pn-np/bc/glacier/visit/a7.aspx Parks Canada (2011) Glacier National Park. Avalanche Terrain Maps, Connaught Creek. Retrieved November 24, 2011 from http://www.pc.gc.ca/eng/pn-np/bc/glacier/visit/visit5/aval/a10b.aspx