Use a “~” in the notebook when no observation was made. Code as “U” if the observation was attempted but no reliable value could be ascertained. Do not leave blanks. Only write “0” when the reading is zero.
A full snow profile is a multi-observation record of snow-cover stratigraphy, including characteristics of individual layers and layer interfaces. It is recorded on a study plot and observed at standard or intermittent time periods.
Objectives.
Location.
Equipment.
Note: Keep all observation equipment in the shade and wear gloves when handling the instruments.
Procedure.
Observations:
Where:
5. When multiple samples within one layer are averaged, the resulting value is described as “average layer density”. Density measures that include more than one layer are described as “bulk density”.
Optional Calculations:
Full Snow Profile Example:
Objectives. Test Snow Profiles contain only observations relevant to assessing current slope snow stability. Snow penetrability, liquid content, and layer densities are usually omitted.
Location. Test profiles are often observed where snow conditions are similar to avalanche starting zones. When selecting a site, keep in mind that elevation and exposure to wind and sun are the strongest factors influencing the variations of snow cover. Profile locations should be at least 5m from the tip of tree branches and not be in a depression, and not contain avalanche debris or tracks from skis, vehicles, or animals. Safety considerations are paramount; consider the potential hazard of avalanches from above and below.
Test Profile Example:
Objectives. Fracture Line Snow Profiles are full or test snow profiles taken near the crown or flanks of slab avalanches. They are used to identify which layers were of prime importance in causing the avalanche (slab layers, weak layers, and base layers), as well as which terrain and weather conditions may have contributed to the snowpack’s condition.
Observations may be taken at both the thick and thin sections of the fracture line, and supplementary information on strength and stability may be obtained from a similar undisturbed site.
Procedure.
Recording. Important information includes:
Objectives. The Ram profile records the relative harness of snow layers measured with a Ram penetrometer. It can be applied on its own as an index of snow strength, but it is not recommended for use in snow stability. When used in combination with a snow profile, the Ram profile should be taken about 0.5 meters from the pit wall after observations of the snow profile, but before any shovel shear tests. In two stage profiles (deeper than 2m), the Ram is inserted to the ground in the corner of the hole to reference the layer boundaries from the ground. Then the deeper stage is dug along the lower Ram sections.
Note: The Ram profile has two distinct shortcomings when used in snow stability work:
Equipment. The Ram penetrometer consists of the following:
The mass of hammer chosen depends on the expected harness of the snow and desired sensitivity.
Unit of Measurement. Ram hardness is measured in Newtons. Acceleration due to gravity is 9.81m/s2, however for Ram hardness calculations it is approximated to 10m/s2.
Procedure.
Calculation.
Where:
Example:
Snow profiles can be represented graphically in a standard format for quick reference and permanent record.
Example:
Objectives. The shear frame test is an index observation of the stability of weak layers, including those in new or partially decomposed or fragmented snow.
Site Selection. The sheer frame test is performed together with snow and weather observations on a study plot. The observation site must be level, and the snow surface must be undisturbed by wind for meaningful and reproducible test results.
Equipment. The shear frame test requires the following equipment:
Procedure Part 1: Locate the weak layer. There are several ways to find a weak layer. This method described is for using tilt boards.
Procedure Part 2: Shear frame test.
Results.
Limitations.
Objective. The rutschblock test is one of the most reliable snow stability tests. It is a mini slab avalanche tested with a skier or a snowboarder, and is therefore best related to human triggering. The sample size is larger compared to other snow stability tests, which makes the rutschblock test more reliable.
Site Selection. Test sites should be safe, undisturbed, and representative of the avalanche terrain under consideration. The site should not contain buried ski tracks, avalanche deposits, or be within about 5m of trees. The slope angle should equal to or greater than 25o. Be aware that near the top of a slope, snowpack layering and hence rutschblock scores may differ from the slope below.
Equipment. 8m of 4-7mm cord with overhand knots tied every 20 or 30cm can be used to cut the upper wall and both sides of the block at the same time (provided no hard crusts are encountered. Long rutschblock-specific snow saws are useful to cut hard crusts.
Procedure.
Recording. Record data code, release type, reference point, location in profile, weak layer properties (form, size, date of burial), and comments. The exact percentage of the block which released can be recorded in the comments.
Limitations.
Objective. The shovel shear test is used to search for instabilities in the snowpack and assess their weak-layer strength.
Site Selection. Select a site that has undisturbed snow and is representative of the slope of interest. Look for neutral, open areas at mid slope without wind effects. Don’t dig it along ridgelines where the wind has affected the snow, and avoid thick trees because conditions are often quite different than on open slopes. Avoid places where people have compacted the snow.
Equipment.
Procedure.
Recording.
Limitations. This test does not produce useful results in layers close to the snow surface. Soft snow near the surface is better tested with the tilt board and shear frame test. Also, the ratings of the effort are highly subjective and depend greatly on the user’s shovel dimensions.
Objective. The compression test is most effective at finding weak layers near the surface. Manual taps applied to a shovel blade placed on top of a snow column cause weak layers within the column to fracture, and these fractures can be seen on the smooth walls of the column. This test can be performed on level or sloping terrain.
Site Selection. Select a site that has undisturbed snow and is representative of the slope of interest. Look for neutral, open areas at mid slope without wind effects. Don’t dig it along ridgelines where the wind has affected the snow, and avoid thick trees because conditions are often quite different than on open slopes. Avoid places where people have compacted the snow.
Equipment.
Procedure.
Recording. Record data code, number of taps, fracture character, reference point, location in profile, weak layer properties (form, size, date of burial), and comments.
Limitations. Deeper layers (>100cm) are less sensitive in compression tests, resulting in higher ratings. The compression test also may not produce useful results for weak layers that are very close to the snow surface (<10cm).
Objective. The deep tap test is used to determine the fracture character of a weak layer that is too deep for a compression or shovel shear test (>120cm).
Site Selection. Select a site that has undisturbed snow and is representative of the slope of interest. Look for neutral, open areas at mid slope without wind effects. Don’t dig it along ridgelines where the wind has affected the snow, and avoid thick trees because conditions are often quite different than on open slopes. Avoid places where people have compacted the snow.
Equipment.
Procedure.
Recording. Record data code, number of taps, fracture character, reference point, location in profile, weak layer properties (form, size, date of burial), and comments.
Limitations. While very effective for testing deeper weak layers, the number of taps required to initiate failure has never been correlated with skier-triggered avalanches on adjacent slopes. However, the fracture character observations have been verified and may be interpreted as in the compression test.
Objective. The extended column test quickly indicates the tendency of slab and weak layer combinations in the upper snowpack (<1m) to propagate a fracture. It is a good test prior to a compression test to see where fractures might occur.
Site Selection. Select a site that has undisturbed snow and is representative of the slope of interest. Look for neutral, open areas at mid slope without wind effects. Don’t dig it along ridgelines where the wind has affected the snow, and avoid thick trees because conditions are often quite different than on open slopes. Avoid places where people have compacted the snow.
Equipment.
Procedure.
Recording. Record data code, number of taps, reference direction (down = from surface, up = from ground), location in profile, weak layer properties (form, size, date of burial), and comments.
Limitations. The extended column test is not good at assessing mid-storm shear layers, or soft (F+ or less) upper layers of the snowpack. In these cases, the shovel edge tends to cut those soft layers It is also not a good tool to asses fracture tendency on weak layers deeper than 100cm.
Objective. The propagation saw test aims to indicate the tendency of pre-identified slab and weak layer combinations to propagate a fracture.
Site Selection. Select a site that has undisturbed snow and is representative of the slope of interest. Look for neutral, open areas at mid slope without wind effects. Don’t dig it along ridgelines where the wind has affected the snow, and avoid thick trees because conditions are often quite different than on open slopes. Avoid places where people have compacted the snow.
Equipment.
Procedure.
Recording. Record PST, cut length, column length, data code, reference direction (down = from surface, up = from ground), location in profile, weak layer properties (form, size, date of burial), and comments.
Limitations.
Objective. Fracture characters describe how the shear fracture propagated in the test column. It adds some value to the interpretation with respect to instability.
Procedure. The front face and side walls of the test column should be as smooth as possible. The observer should be positioned such that one side wall and the entire front face can be observed. Attention should be focused on the weak layers likely to fracture.
For tests on low-angled terrain that produce planar fractures, it may be useful to slide the two fracture surfaces across one another by carefully grasping the sides of the block and pulling while noting the resistance.
Use the following table to characterize the fracture:
Recording. Record fracture character in brackets following the test’s data code. If multiple tests at the same site produce results on the same layer, record results as follows: data code 1, fracture character 1, data code 2, fracture character 2, etc…, reference point, location in profile, weak layer properties (form, size, date of burial), comments.
Objectives. Snowpack summaries provide a clear and concise overview of the snowpack conditions. The objective is to organize and reduce data. They are not recorded at a specific location and time, but are a general characterization of the range of conditions encountered in the broader area of the day. This not only includes average conditions bust also potential anomalies.
Frequency. Generally done once a day, at the end of the day.
Procedure. The following parameters should be recorded in a snowpack summary: