ISSW'98
Poster Session
Mountain Snowpack
Distributed Observations of Snow Accumulation and Avalanche Response
Susan A. Burak
Snow Survey Associates, P.O. Box 8544, Mammoth Lakes, CA 93546; email. sburak@qnet.com
Eddy Bouzaglou
Mammoth Mountain Ski Resort, Mammoth Lakes, CA
Robert E. Davis
U.S. Army Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, New Hampshire 03755-1290
In terms of avalanche activity, storm cycle characteristics depend on the interaction of meteorological variables at the synoptic scale and terrain factors at the local scale. These control the spatial distribution of snow fall accumulation and redistribution. We describe relations between storm cycle characteristics and avalanche activity through the use of observations from an array of snow boards, distributed across a wide range of slopes and aspects at Mammoth Mountain, California. Snow accumulation on each board was measured during and at the end of each major storm cycle during the winters 1996-1997 and 1997-1998. Avalanche observations derived from the standard reporting procedure developed by the US Forest Service, and maintained at Mammoth by the resort ski patrol. Weather factors were obtained from standard charts published by the National Weather Service. Patterns of storm intensity and direction left clear signals in terms of different accumulation records on the snow boards. This in turn was reflected in avalanche response to natural triggering, explosive control and ski cutting. We show how a distributed series of snow boards could provide indications of the relative distribution
of avalanche activity over a local scale area.
Wet Snow Pendular Regime: The Amount of Water in Ring-Shaped Configurations
A. Denoth
Institute of Experimental Physics, University of Innsbruck, Technikerstrasse 25 / 4, A-6020, Innsbruck, Austria; tel. 43-512-507-6317; fax. 43-512-507-2921; email. Armin.Denoth@uibk.ac.at
The water saturation of a natural snow cover varies, in general, from zero to approximately 20% of the pore volume, whereby two essentially different types of water geometry - pendular mode and funicular mode - can be observed. The pendular mode covers the low-saturation range (typically S
£ 7% for old Alpine snow) and it is assumed that the water component is arranged in isolated menisci or pendular rings around a contact zone between spheroidal ice grains. However, the the water rings or menisci are, thermodynamically, in a very critical - may be in an unstable - configuration.As water rings or menisci represent closed electrically conducting loops, they may be respon-sible for an induced diamagnetic behaviour of snow, especially in the microwave regime; and this offers a way to measure the amount of water stored in these geometrical configurations. From a carefull analysis of the measured dielectric and magnetic permeability in the microwave X- to K-bands of moderate wet coarse grained Alpine snow results, that water rings seem only to exist at saturations lower than
»2.5%. For saturations exceeding this critical value, water rings begin to merge forming clusters, whereby the number of ring-like geometries decreases in favour of larger but open-ended structures.
Statistical Comparison of Rutchblock Stability Test with Skis and Snowboard (Shredblock test)
Andy Gleason
Colorado Avalanche Information Center, 10230 Smith Road, Denver, CO 80239
tel. 303-371-1080; fax. 303-371-5508; email. silverav@frontier.net
Snowboarders are a winter backcountry user group whose incidents of avalanche accidents and fatalities are increasing every year. The avalanche community needs to address this group with avalanche education. While teaching snowboarders about snow stability, there needs to be a test that can be easily conducted using a snowboard. The Rutchblock test can be easily and efficiently performed with a snowboard (herein referred to as the Shredblock Test).
Data were collected for the past three winters(1995-1998) in the San Juan Mountains of Colorado, comparing the Rutchblock test with the Shredblock test. Test pits were dug side by side on a variety of aspects, elevations and slope angles. Persons of comparable weight were used to conduct the tests. The criteria for the Shredblock test was the same as for the Rutchblock, using the 7 step method (Fohn, 1987). The width of the isolated column was reduced to the length of the snowboard (170 cm). The depth remained the same at 1.5 m.
Results indicate that the Shredblock test correlates well with the Rutchblock test for determining depth to weak layers and their relative strength. At lower levels in the snowpack (greater than 0.5 meters in depth from the surface), Rutchblock and Shredblock results are almost identical. Near the surface however, the Shredblock test detects more potential shear planes in some snowpacks, due to less penetration of the low density surface snow by the snowboard. During Rutchblock tests, the skis often penetrate 20 to 40 cm down from the surface, and therefore are unable to detect any weak layers in the upper snowpack. The snowboard, because of it's larger surface area, does not penetrate as deeply and therefore could be more useful for detecting near surface weak layers.
Comparison of Chemical Loading to the Colorado Rocky Mountain Snowpack with Annual Wet Deposition Data Collected as Part of the National Atmospheric Deposition Program
K. Heuer
National Park Service, P.O. Box 25287, Denver, CO 80225; tel. 303-987-6941; email. kristi_heuer@nps.gov
K. Tonnessen
National Park Service, P.O. Box 25287, Denver, CO 80225; tel. 303-969-2738; email. kathy_tonnessen@nps.gov
G. Ingersoll
USGS-WRD, MS 415, DFC, Denver, CO 80225; tel. 303-236-4882 (x292); email. gpingers@usgs.gov.
The US Geological Survey and National Park Service have cooperatively monitored snowpacks along the Continental Divide in the Rocky Mountains from 1993-1998, measuring total chemical loads at maximum accumulation. At 62 snow survey sites, adjacent to SnoTel sites, we dug snowpits in late March-early April to estimate the chemical concentrations of major anions, cations, trace metals, and sulfur isotopes. The objective of this work is to amass long-term data on the distribution of pollutants to snowpacks to allow us to set critical loads for nitrogen and sulfur. These are the chemicals that can cause changes in surface water chemistry of high-elevation lakes, streams and ponds in sensitive watersheds. NADP sites in the Rocky Mountains provide us with weekly chemical loading estimates during all seasons of the year. Our comparison of the NADP and snow survey data at a number of high elevation sites in the Colorado Rockies has shown that winter frontal storms deposit larger amounts of chemicals in snow on the western slope. During the spring and summer seasons, upslope meteorological conditions result in more loading of N and S to eastern slope locations. We have also been able to identify interannual patterns of chemical deposition related to total rain and snowfall.
Experiments of Depth Hoar Formation under Extremely Low Temperature
Y.Kamata
Shinjo Branch of Snow and Ice Studies, NIED, Shinjo, Yamagata 996, Japan
M.Takahashi
Weathernews International Company, Chiba, Chiba 262, Japan
A.Sato
Shinjo Branch of Snow and Ice Studies, NIED, Shinjo, Yamagata 996, Japan; tel. +81-233-22-7550; fax. +81-233-22-7554; email. asato@nieds.shinjo.bosai.go.jp
To investigate the growth of depth hoar crystals in a very cold region, two experiments were carried out for about three days with the temperature gradients of 300K / m, and 500K / m. In this experiments, two snow samples were subjects of upward and downward temperature gradients at the same time.
After three days of the thermal conditions, snow samples were divided into three layers. Photographs of the snow grains were taken using microscope for each layer. The mean cross-sectional area of the digitized grains was determined as a diameter of a circle with an equivalent area. Snow crystals of these layers were also classified into three types: original type, solid type, and skeleton type. Growth direction of depth hoar crystal was also observed by vertical thin section for each layer.
From these experiments it became clear that the texture of original fine snow was considerably changed into sharply edged hoar grains. They were solid and skeleton types due to dry metamorphism under both upward and downward temperature gradient. Crystals which were subjected to the coldest temperature were not different from initial ones. These type of depth hoar were strongly affected by temperature of the spot rather than temperature gradient. These depth hoar grew toward warmer part no matter either the temperature gradient was upward and downward.
Basal Stress Measurements of Artificial Avalanches
K. Kosugi, O. Abe, and A. Sato
Shinjo Branch of Snow and Ice Studies, National Research Institute for Earth Science and Disaster Prevention, Shinjo 996-0091, Japan; tel. 81-233-23-8005; fax. 81-233-23-3353; email. kosugi@shinjo.bosai.go.jp
Y. Nohguchi
National Research Institute for Earth Science and Disaster Prevention
K. Nishimura, Y. Ito, and M. Nemoto
Institute of Low temperature Science, Hokkaido University
K. Izumi
Research Institute for Hazards in Snowy Areas, Niigata University
Measurements of basal stress of artificial snow avalanches in motion were carried out with a drag meter at an experimental chute and a ski jump. A mass of snow of which weight was 300 kg at maximum was released at the top of the slope to produce a snow avalanche. The drag meter, composed of a three components loadcell and a metallic plate, was installed on the slope near its lower end. The normal and tangential components of the basal stress exerted on the slope by the avalanches were recorded. The results showed a characteristic change in the basal stress with relation to the position in the avalanche body. The basal stress increased rapidly when the head of an avalanche reached the drag meter. The dynamic friction coefficient, the tangential component divided by the normal component of the basal stress, was relatively small, ranging 0.2 to 0.6. From the middle to the tail of the avalanche, the basal stress decreased and the dynamic friction coefficient increased from 0.4 to 1.0. The density of the middle part of the snow avalanches was estimated at 80 kg/m3 with the normal stress and the thickness. Basal stress measurements were also conducted for avalanches of thousands of table tennis balls at two points on the experimental chute. The basal stress increased and decreased monotonously during the pass of the avalanches at the upper point. At the lower point, the change in basal stress with time was similar to that obtained for snow avalanches mentioned above. The difference in the basal stress between the two points is probably caused by the change in the structure of the avalanche as it flows down.
Rime and Glazed Frost Formation in the Khibini Mountains
Eugeny Mokrov
Centre of Avalanche Safety of "Apatit" JSC, 33a, 50 years of October st., Kirovsk, 184230, Murmansk region, Russia; tel. 78153196230; fax. 78153196200
Climatic conditions of the Khibini Mountains are favorable for the rime and glazed frost formation:
I. long cold period (up to 260 days per year);
II. high air humidity (up to 309 days per year with relative humidity more than 80 %);
III. great number of days with fogs (up to 310 days per year);
IV. significant wind speeds during fogs (10 - 15 m/s);
V. predominant temperature regime (from 0 to -100 C).
More 2400 occurrences of rime and glazed frost formation were studied. The compatible statistical analysis of rime and glazed frost occurrences and an extensive data base of three-hourly meteorological observations (1962 - 1997) at the mountain top are presented.
The Growth of Near-Surface Faceted Crystals and Their Effect on Snow Stability, Red Mountain Pass Corridor, Colorado
Joe Stock
Department of Earth Resources, Colorado State University, Fort Collins, CO 80523-1482; fax. 970-91-6307; email. stock@cnr.colostate.edu
Kelly Elder
Department of Earth Resources, Colorado State University, Fort Collins, CO 80523-1482
Karl Birkeland
Gallatin National Forest Avalanche Center, P.O. Box 130, Bozeman, MT 59771
Avalanches are important as a natural hazard to humans and anthropogenic structures. Slab avalanches fail from weak layers such as surface hoar, graupel, or faceted crystals. One important type of faceted crystal forms in the near-surface layers, called near-surface faceted crystals. During the 1997/98 winter a study of near-surface faceted crystals was conducted along the Red Mountain Pass corridor between Silverton and Ouray, Colorado. Six types of near-surface faceted crystals were differentiated: solid-type, radiation recrystallization crystals, faceted precipitation crystals, near-surface hoar, faceted partly-decomposed precipitation crystals, and needles. Near-surface faceted crystals can form in any type of dry snow. Previous research in the area has shown that crystal faceting occurs when vapor pressure gradients are greater than 5 mb/m. After burial, near-surface faceted layers can reduce snow stability, occasionally resulting in persistant weak layers. For example, a particularly well-developed near-surface facet layer that evolved in December acted as the dominant weak layer in the study area for 7 weeks. Observation of 14 avalanches showed that 79% of the failures occurred on near-surface faceted layers. The majority of all stability test failures occurred on near-surface faceted layers. Understanding the growth of near-surface faceted crystals and their effect on snow stability is important for avalanche forecasting.
Webmaster: mark.moore@noaa.gov