Chapter 3: Snowpack Observations

Recording

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.

Full Snow Profile

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.

To identify the weak and strong layers that make up the snowpack.
To identify weak interfaces between layers and to determine their relative strength.
To observe snow temperatures.
To monitor and confirm changes in the condition, stratigraphy, temperature, and stability of the snowpack.
To determine the thickness of a potential slab avalanche.
To determine the state of metamorphism of the snow.

Location.

Study Plot. Full snow profiles are carried out at study plots by excavating each snow pit progressively in undisturbed snow. Excavation is parallel to a line marked with two poles indicating the extreme edge of the previous snow pit, and at a distance from the previous snow pit equal to the snow depth or at least 1 meter away. After each observation the extreme edge of the pit is marked with a pole to indicate where to dig next. The snow profile observation line should be selected and marked before winter, and the ground between the marker poles cleared of brush and large rocks.
On Slope. The best information with respect to snow stability is obtained from snow profiles taken at avalanche starting zones. Since starting zones are not always accessible, other slopes should be selected provided that they are undisturbed, safe, and representative of the conditions in starting zones. These study slopes may be pre-selected and marked in the same manner as study plots; however, marker poles on slopes will be tilted by snow creep and may have to be periodically reset. 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.

Equipment.

Probe
Shovel
Digital thermometer
Ruler
Loupe
Crystal screen
Snow density cutter and scale
Field book
Pencil
Gloves
Compass
Altimeter
Inclinometer
Snow saw
Brush
Camera
GPS
Calculator
Safety rope

Note: Keep all observation equipment in the shade and wear gloves when handling the instruments.

Procedure.

Check Snow Depth. Make sure the pit is clear of boulders or brush, and is not in a depression. Feel the hardness of the snow with the probe and obtain an indication of the stratigraphy and total snow depth.
Dig the Pit. Make the pit wide enough for multiple observations (2-3m). In snow deeper than 2m, first dig to a depth of 1.5 meters, make the observations, then complete the excavation and finalize the observations. Pile extracted snow so that it does not reflect solar radiation into the observation pit. The pit face and side on which the snow is to be observed must be in the shade. Cut the observation face and adjacent side diagonally with a snow shovel, then smoothen with gloved hands. Make the face parallel to the fall line. While the first observer prepares the pit, the second observers begins observations.

Observations:

Title: Location, elevation, aspect, slope inclination.
Date: yyyy-mm-dd
Time: 24-hr time local time.
Observers: Initials, with the primary observer first.
Air Temperature. Observe the air temperature in the shade about 1.5m above the snow surface. Use a dry thermometer, read after about five minutes, wait another minute and read again.
Sky Condition. Classify amount of cloud cover with one of the symbols below:With Valley Fog, estimate the elevation of the bottom and top of the fog layer in meters above sea level. Given the elevation to the nearest 50 m. Data code is VF with bottom and top elevations separated by a hyphen.When the sky condition features a thin cloud layer, precede the symbol with a dash.
Precipitation Type. Record the type of precipitation at the time of observation.
Precipitation Intensity. Record the precipitation intensity in centimetres of snow per hour.
Wind Speed and Direction. Estimate the wind speed and direction by observing the motion of the trees and snow. If the wind direction is erratic, record as Variable (VAR). Write “Calm” if the wind speed is calm. Canada records wind speed in km/h, wheres SI units are in m/s.
Blowing Snow. Estimate the current extent of blowing snow and note the direction to the closest cardinal point of the compass.
Surface Penetrability (P). Record the snowpack’s ability to support a given load by using one of the following three tests. Note that Ram Penitration is the preferred observation because it produces more consistent results than ski or foot penetration.
- Ram Penetration (PR): See Ram Profile header below.
- Foot Penetration (PF): Step into undisturbed snow and gently put full body weight onto one foot. Measure the depth of the footprint to the nearest centimetre from 0-5cm and thereafter to the nearest increment of 5cm. Note that it is recommended that all observers working on the same program compare their foot penetration. Observers who continually produce penetrations more than 10 cm above or below the average should not record foot penetrations.
- Ski Penetration (PS): Step into undisturbed snow and gently put full body weight onto one ski. Measure the depth of the ski track to the nearest centimetre

Snow Temperature (T). Push the thermometer parallel to the snow surface (use the shaded-side wall of the pit on a slope). Wait at least one minute, then read it with the tip still in the snow. Measure the first sub-surface snow temperature 10cm below the snow, then continue observations in intervals of 10cm from the previous measurement to 1.4m, then in 20cm intervals to the ground. Closer measurements can be made when the gradients are strong.
Layer Boundaries (H). Record the depth and date of each major layer boundary using a combination of visual and tactile techniques. A brush helps.
Snow hardness (R). Observe the relative harness of each layer with the hand test. Slight variations in hand harness can be recorded using + and – quantifiers.

Surface Grain Form (F). Estimate as per the International Standard using the following table. In warm weather the crystals may melt and their shape may rapidly change. In this case, take repeated samples from various depths of the same layer. (Source PDF; Downloadable PNG; Downloadable PDF).
Surface Grain Size (E). Determine the grain size of the surface particles. Disregard small particles and determine the average greatest extension of the grains that make up the bulk of the snow. Record size to the nearest 0.5mm, except for fine or very fine grains which may be recorded as 0.1, 0.3, or, 0.5mm. Where two distinct grain forms exist, record the size of the secondary grain in brackets. Where a range in sizes exist for a single grain form, specify the minimum and maximum size separated by a hyphen. The following table contains terms that describe grain size, however they should not be used in field notebooks:
Liquid Content (θ). Classify liquid water content by volume of each snow layer that has a temperature of 0^o Gently squeeze a sample of snow and observe the reaction.
Density (ρ). Measure density of the snow in layers that are thick enough to allow insertion of the snow density cutter. Tube- or box-shaped cutters should be used for thin layers as described:
1. Sample densities from the pit face on flat terrain and from the pit sidewall when on an incline.
2. Insert tube- or box-shaped cutters horizontally and wedge- or small-shaped tube cutters vertically. Do this perpendicular to the layering when on an incline. When inserting cutters vertically, clear the snow from above and place a flat cutter or crystal screen at the depth equal to the long axis dimension.
3. Trim the ends, remove excess external snow, and weigh. Volume of thin layers that do not fill the tube cutter can be calculated in the same manner as using a tube for new snow density (area of tube opening x layer thickness).
4. Record weight and cutter volume under comments. Calculate density as follows:

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”.

Strength and Stability Tests. Record strength and stability tests. See Chapter 4: Weak Layer Strength and Stability Tests for their descriptions.
Mark the Site. Fill the pit and place marker poles at the extreme edge if you plan to undertake further studies at that size.

Optional Calculations:

Water Equivalent of Snow Cover (HSW). The water equivalent is the vertical depth of the water layer which would form if the snow cover was melted.

Average Bulk Density.

Full Snow Profile Example:

Test Snow Profile

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:

Fracture Line Snow Profile

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.

Use a sketch or photograph to describe the location. Carefully describe terrain features, vegetation, and sun and wind effects on the snowpack. Note any evidence of past avalanche activity which may have influenced the snowpack’s structure.
Dig the observation face into undisturbed snow at least 1.5 meters back into the crown or flank. Dig down below the depth of the bed surface.
Note the location of, and the crystal shape, grain size, and temperature in the initial failure plane and bed surface.
Measure the incline of the terrain with an inclinometer.
Record the exact location of the profile with respect to the avalanche fracture geometry.

Recording. Important information includes:

The strength of the weak layer and the effect of loading from the layers above.
Grain form and grain size in the weak layer.
The snowpack temperature gradient.

Ram Profile

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:

It often fails to identify thin weak layers in the snowpack.
Its sensitivity is dependent on the hammer and tube weights, particularly hen used in soft or very soft snow.

Equipment. The Ram penetrometer consists of the following:

A sectional tube with a cone of 40mm diameter and an apex angle of 60^o.
Multiple extension tubes.
A guide rod.
A hammer of mass 2kg, 1kg, 0.5kg, 0.2kg, or 0.1kg.

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.

Type and weight of Ram and hammer. Obtain weight by multiplying approximate mass by 10.
Drop the hammer and count the number of blows. One person works the Ram and counts the number of blows; while the other person observes depth of penetration and writes all the information.
1. Let the first sectional tube slowly penetrate the snow under its own weight. Record its weight in column T + H. Read the penetration and record it in column
2. Add the guide rod and hammer. Record its weight plus the hammer in column T + H. Read the penetration and record it in column
3. Drop the hammer from a height between 1 and 5 cm and note the penetration. Continue dropping the hammer from the same height until rate of penetration changes. Record fall height (f), number of blows (n), and penetration (p) up to the point before rate of penetration changes.
4. Continue with another series of blows, choosing a fall height that produces a penetration of about 1cm per blow.
5. Add another section of tube when necessary and record the new T + H.

Calculation.

Calculate the increment of penetration (p) for each series of blows.
Calculate Ram hardness (R) with:

Where:

R = Ram hardness (N)
n = Number of hammer blows
f = Hammer fall height (cm)
Δp = increment of penetration for n blows (cm)
T = Weight of tubes including guide rod (N)
H = weight of hammer (N)

Plot on graph paper the Ram hardness versus depth of snow.

Example:

Graphical Snow Profile Presentation

Snow profiles can be represented graphically in a standard format for quick reference and permanent record.

Plot snow temperatures as a curve; mark the air temperature above the snow surface.
Plot distance of snow layers from ground or snow surface to scale.
Use graphical symbols for the shapes of grains and liquid water content. Plot a ~ when hardness or liquid water content could not be determined. Use of graphic symbols for hardness is optional.
Tabulate grain size and density with values observed in the field.
Include written comments where appropriate. If possible, label important layers by their date of burial.
Include results of strength and stability tests in the comments column. Document grain form and size of the failure layer. Draw an arrow at the height of each observed fracture and use shorthand notation to describe the test.
When Ram data is not taken, plot the hand test results of snow hardness as a horizontal bar graph, using the following lengths of parts for scale:

Example:

Sheer Frame Test

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:

Metal cutting plate about 30cm x 30cm
Shear frame, usually 100 or 250 cm² in area
Force gauge, maximum capacity 10 to 25 N
Snow sampling tube
Weight scale
Ruler
Tilt board (optional)

Procedure Part 1: Locate the weak layer. There are several ways to find a weak layer. This method described is for using tilt boards.

Cut a block of undisturbed snow with sides about 30cm x 30cm, and 30-40cm of depth. A second deeper block of similar size must be collected if the suspected failure plane is deeper than 40cm.
Lift the snow block with the cutting plate onto the horizontal tilt board.
Tilt the board to an angle of 15^o. Tap the board gently until a shear fractures occurs.
Measure depth of the failure plane from the surface at the side of the block; record under “Sheer depth”.
Collect a sample of snow on the tilt board by inserting the sampling tube (perpendicular to the snow surface) to the depth of the failure plane. Weigh sample and record net weight under “Sheer weight”.
Establish location of the failure plane in the snowpack by measuring shear depth from the surface.

Procedure Part 2: Shear frame test.

Remove overlying snow with a cutting plate, leaving a few centimetres of undisturbed snow above the failure plane.
Gently push the shear frame down through the snow to a few millimetres above the failure plane by holding it with the thumb and index finger.
Zero the force gauge, then hook it to the frame and pull parallel to the failure plane. Read and record the force required to produce a fracture.
Repeat the procedure several times to confirm consistency.

Results.

Note the area of the shear frame and the cross-section area of the sampling tube.
Determine shear strength by dividing the force (g) at fracture by the area (cm²) of the shear frame.
Determine weight of snow per unit area by dividing weight (g) of the snow sample by the cross-sectional area (cm²) of the sampling tube.
Calculate stability ratio by dividing shear strength by weight per unit area.

Limitations.

Units of Measurement. Stability ratio has no units of measurements. However, it is preferable to use SI units rather than metric units in its calculation. With SI units the shear force should be expressed in Newtons and the shear frame index in Pascals.
Experience is required to produce reliable data. Success of the test depends on:
- Carefully removing the snow block above without disturbing the layer to be tested.
- Inserting the shear frame parallel and close to the failure plane without causing premature fracture.
- Pulling the shear frame at a constant rate.

Rutschblock Test

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 25^o. 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.

After identifying weak layers and potential slabs in a snow profile, extend the pit wall until its width is at least 2m minimum across the slope.
Mark width of the block and length of the side cuts on the surface of the snow with a ski or ruler. The block should be 2m wide throughout if the sides of the block are to be dug with a shovel. However, if the side walls are to be cut with a ski, pole, cord, or saw, the lower wall should be about 2.1m across and the top of the side cuts should be about 1.9m apart. This flaring of the block ensures it is free to slide without binding at the sides. The side cuts should extend 1.5m up the slope.
The lower wall should be a smooth vertical surface cut with a shovel. Dig or cut the side walls and the upper wall deeper than any weak layers that may be active. If the side walls are exposed by shovelling, then one rutschblock test may require 20 minutes or more for two people to perform.
If the weak layer of interest are within 60cm of the surface, save time by cutting both the sides and upper wall of the block with a ski pole (basket removed) or with the tail of a ski. If weak layers are deeper than 60cm and the overlying snow does not contain any knife-hard crusts, both the sides and upper wall of the block can be sawed with cord which travels up one side, around ski poles or probes placed at both upper corners of the block, and down the other side.
Once completely isolated from the surrounding snowpack, the block is progressively loaded by a person on skis or snowboard using the following table:
When observing rutschblock tests, observe the amount of block that releases for each weak layer fracture according to the following table:
Indicate the reference point for the fracture position (down = from surface; up = from ground) and measure the location of the fracture in the profile. The snow surface is the default reference point for measuring fracture location.

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.

The rutschblock only tests those layers deeper than ski or snowboard penetration (>20cm).
Higher and more variable rutschblock scores are sometimes observed near the top of slopes where the layering may differ from the middle and lower part of the slope. Higher scores may contribute to an incorrect decision.
Effect of Slope Angle. Rutschblock results are easiest to interpret if the tests are done in avalanche starting zones. However, since there is a tendency for rutschblock scores to increase by 1 for each 10 degree decrease in slope angle, scores for avalanche slopes can be estimated from safer, less steep slopes as shallow as 25^o.
- Rutschblocks done on slopes of less than 30^o require a smooth lower wall and a second person standing in or near the pit to observe the small displacements (often less than 1cm) that indicate a sheer fracture.

Shovel Shear Test

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.

Probe
Shovel
Snow saw
Ruler
Loupe
Crystal screen
Field book
Pencil
Gloves

Procedure.

Expose a fresh pit wall by cutting back about 20cm from the wall of the snow profile.
Remove any very soft snow from the surface of the area where the test is to be carried out.
Mark a cross-section of the column to be cut on the snow surface, measuring 25cm across and 35cm up.
Cut a chimney wide enough to allow the insertion of the saw on one side of the column and a narrow cut on the other side.
Make a vertical cut at the back of the column and leave the saw at the bottom for depth identification. The back-cut should be at maximum 0.7m deep, and end in hard snow. If necessary, remove a wedge of snow near the surface at the top of the back-cut so that the shovel bend fits cleanly.
Carefully insert the shovel into the back-cut. Hold the shovel with both hands and apply a pull force in direction of the slope.
When a clean shear fractures occurs in the column above the low end of the back-cut, mark the level of the failure plane on the rear wall of the back-cut.
When a clean shear or irregular fracture occurs in the column at the low end of the back-cut, or when no fracture occurs, remove the column above the bottom of the back-cut and repeat steps 5-7 on the remaining column below.
Repeat the test on a second column with the edge of the shovel 0.1m-0.2m above the suspected weak layer.
Measure and record the depth of the failure planes if they were equal in both tests. Repeat steps 3-8 if the failure planes were not at the same depth in both tests.
If no fracture occurs, tilt the column and tap.
Use the following chart to determine the approximate effort necessary to shear the snow:
Use the following chart to determine the fracture character of the snow shear:
Indicate the reference point for the fracture position (down = from surface; up = from ground) and measure the location of the fracture in the profile. The snow surface is the default reference point for measuring fracture location.
Observe, classify, and record crystal shape and size at the failure planes (crystal samples are best obtained from the underside of the sheared block.

Recording.

Record data code, fracture character, reference point, location in profile, weak layer properties (form, size, date of burial), and comments.
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.

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.

Compression Test

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.

Equipment.

Probe
Shovel
Snow saw
Ruler
Loupe
Crystal screen
Field book
Pencil
Gloves

Procedure.

Isolate a 30cm x 30cm column of snow deep enough to expose potential weak layers. The uphill dimension is measured slope-parallel. A depth if 100cm – 120cm is usually sufficient since taller compression tests rarely produce fractures in deeper weak layers.
Rate any fractures that occur while isolating the column as very easy (CTV).
Place a shovel blade on top of the column. Tap 10 times with fingertips, moving hand from wrist, and rate any fractures as easy (CTE).
If the snow surface slopes, remove a wedge of snow to level the top of the column.
If, during tapping, the upper portion of the column slides off, or no longer evenly supports further tapping, remove the damaged part of the column, level the new top of the column and continue tapping. Do not remove the portion of the column above a fractured weak layer, provided that it evenly supports further tapping.
Tap 10 times with the fingertips moving forearm from the elbow, and rate any fractures as moderate (CTM).
Finally, hit the shovel blade moving arm from the shoulder 10 times with open hand and rate any fractures as hard (CTH). Rate any identified weak layers that did not fracture as no fracture (CTN).
Measure fracture character, reference point, location in profile, and weak layer properties from the underside of the fractured column.

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).

Deep Tap Test

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).

Equipment.

Probe
Shovel
Snow saw
Ruler
Loupe
Crystal screen
Field book
Pencil
Gloves

Procedure.

Using a snow profile, identify a weak snowpack layer which is overlain by harder snow and is too deep to fracture consistently in the compression test.
Prepare a 30cm x 30cm column as for a compression test (the same column can be used after a compression test, provided the compression did not disturb the target weak layer). Try not to cut the back wall more than a few centimetres below the target weak layer.
Level the column such that only 15cm of snow remains above the target weak layer.
Place the shovel blade (facing up or facing down) on top of the column. Apply 10 light, 10 moderate, and then 10 hard taps as for the compression test. Record as per the table below.
Measure fracture character, reference point, location in profile, and weak layer properties from the underside of the fractured column.

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.

Extended Column 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.

Equipment.

Two probes
8m or 4-7mm cord with overhand knots tied every 20-30cm
Shovel
Snow saw
Ruler
Loupe
Crystal screen
Field book
Pencil
Gloves

Procedure.

Isolate a column of snow 90cm across slope, 30cm up slope, and deep enough to expose potential weak layers. Depth should not exceed 100cm.
Rate any fractures that cross the entire column while isolating as ECTPC.
If the snow surface is hard and inclined. Remove a wedge of snow to level the top of the column at one edge.
Place the shovel blade on one side of the column and apply 10 light, 10 moderate, and then 10 hard taps as for a compression test. Score each fracture according to the following table:
Measure fracture character, reference point, location in profile, and weak layer properties from the underside of the fractured column.

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.

Propagation Saw Test

Objective. The propagation saw test aims to indicate the tendency of pre-identified slab and weak layer combinations to propagate a fracture.

Equipment.

Two probes
8m or 4-7mm cord with overhand knots tied every 20-30cm
Shovel
Snow saw
Ruler
Loupe
Crystal screen
Field book
Pencil
Gloves

Procedure.

When the weak layer is <100cm deep, isolate a column 30cm across slope and 100cm up slope. When the weak layer is >100cm deep, the column length should equal the weak layer depth in the upslope direction. The column should be isolated to a depth below the layer being tested.
Identify the target weak layer by gloving, brushing, or carding along the exposed column wall.
Drag the blunt edge of the saw upslope through the weak layer at a 10-20cm/s speed until the fracture propagates (jumps) ahead of the saw, at which point stop dragging the saw cutting and mark the spot along the layer where propagation began. Use the following table to record the observation:
After observations are complete, remove the column and check that the saw scored the weak layer in the wall behind the test column. If the saw deviated from the weak layer, the test should be repeated.
Measure fracture character, reference point, location in profile, and weak layer properties from the underside of the fractured column.

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.

The propagation saw test tends to five false-stable results for soft shallow slabs and when the weak layer is too difficult to cut with the saw’s blunt edge.
Pre-selecting and identifying the layer of concern for testing can be challenging.
The cut distance may depend on the slope angle.

Fracture Character

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.

Snowpack Summary

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:

Date
Time period
Locations and elevation range
Percent of area observed
Snow profiles summarized, including slab properties, weak layer attributes, and temperature gradients
Stability tests summarized, including fracture character, reference point, location in profile
Comments, including notes on signs of instability, settlement, effects of wind, air temperature, and solar radiations