Field book for snow profile observations

(1)

Liquid water content

Term Symbol Code

Dry: Snow temperature below 0 °C 1

Moist: Snow temperature at 0 °C, water not visible, sticky

 2

Wet: Water can be recognised with a loupe, but cannot be pressed out by moderately squeezing the snow.

 3

Very wet: Water can be pressed out by moderately squeezing the snow.

 4

Soaked: Snow is soaked with water.  5

Snow hardness

Term and hand test Symbol Code

Very soft: fist 1

Soft: 4 fingers  2

Medium: 1 finger  3

Hard: pencil  4

Very hard: knife blade  5

Ice  6

Temperature

Air temperature

Swing thermometer around in air in the shade of your body.

Snow surface temperature

Place thermometer on snow surface and shade it with shovel; thermometer tip penetrates into the snow by maximum 1 mm.

Snow temperature

Measure in the top meter every 10 cm and below every 20 cm.

Concept and text: Gian Darms, Lukas Dürr, Jürg Schweizer

Pictures: SLF Archiv, UNESCO Layout: Sandra Gurzeler, WSL Print: The Federal Department of Defence, Civil Protection and Sport (DDPS)

References

CAA, 2007. Observation guidelines and recording standards for weather, snowpack and avalanches. Canadian Avalanche Association (CAA), Revelstoke BC, Cana- da, 92 pp.

Fierz, C. and 8 others, 2009. The Internati- onal Classification for Seasonal Snow on the Ground. HP-VII Technical Documents in Hydrology, 83. UNESCO-IHP, Paris, France, 90 pp.

Editors

WSL Institute for Snow and Avalanche Research SLF, Davos

Military mountaineering service centre, Andermatt

WSL Institute for Snow and Avalanche Research SLF, Davos Military mountaineering service centre, Andermatt

Field book

for snow profile

observations

(2)

Symbol

(Code) Symbol

(Code) Precipitation part.: 1 – 4 mm a Melt forms: 0.5 – 3 mm h

(1) (7)

Fragmented part.: 1 – 2 mm c Melt-freeze crust: 0.5 – 3 mm Oh (2)

Second grain shape does not necessarily have to be a melt form.

(7–7 o crust)

Rounded grains: 0.2 – 0.5 mm d Ice layer i

(3) (8)

Individual grains are not visible.

Faceted crystals: 0.5 – 3 mm e Rounding faceted particles: C (4) (9)

Depth hoar: 2 – 5 mm f Graupel: 1 – 5 mm o

(5) (0)

Surface hoar: 1 – 10 mm g

(6) part. = particles Notation of grain size

1^stNumber = mean size of all grains 2^nd Number = mean size of largest grains Avalanche size Runout / Typical dimensions Damage potential

Small avalanche (sluff) Stops within steep slope.

Length < 50 m Volume 100 m³

Unlikely to bury a person, except in unfavou- rable runout zones.

In extreme terrain there is a danger of falling.

Medium avalanche Could reach the base of the slope.

Length 50 – 200 m Volume 1000 m³

Could bury, injure or kill a person.

Large avalanche Could traverse low angle terrain (well below 30°) over a distance of less than 50 m.

Length several 100 m Volume 10 000 m³

Could bury and destroy cars, damage trucks, destroy small buildings and break a few trees.

Very large avalanche Traverses flat terrain (well below 30°) over a distance of more than 50 m, could reach the valley floor.

Length 1 – 2 km Volume 100 000 m³

Could bury and destroy trucks and railway cars, and destroy fairly large buildings and small areas of forest.

Extremely large avalanche Reaches the valley floor, largest known avalanche Length > 2 km

Volume > 100 000 m³

Could devastate the landscape, has catastrophic destructive potential.

Grain shape and typical sizes Avalanche sizes

Safety procedures

– Safety first!

– Prepare field trip seriously and according to current conditions.

– Travel in a team of at least two; your partner also needs adequate experience and training.

– Check avalanche bulletin and weather forecast.

– Re-evaluate meteorological conditions, avalanche situation and your schedule regularly during the day. Adapt or cancel field trip if necessary.

– Carry safety equipment (avalanche beacon, shovel, probe; airbag recommended); wear the switched-on avalanche beacon directly on your body. Check transmit function of transceivers before start (Group check).

– Carry additional equipment if circumstances require (means of com munications and orientation as well as technical equipment).

– Approach profile site carefully one by one.

– Do not stay below the column during the rutschblock test.

– Fill all trenches after recording the profile.

– It is recommended to inform a contact person about the intended destination route and return time.

– Beginning of season: Check all safety equipment and practice how to use it.

Emergency telephone numbers

Switzerland

REGA (air rescue) 1414 Emergency medical services 144

International

Europe 112 United States and Canada 911

1 – 3 mm

(3)

1

Snow profile interpretation

– A snow profile provides detailed information on the structure and stability of the snowpack. Stability is best assessed in combination with a stability test.

– Snow profile information is site-specific. Thus, selecting a site representative of the general conditions is essential. Even if the site was chosen carefully, extra polation of observations to other slopes is limited by spatial variability.

– To assess local avalanche danger, the snowpack information has to be combined with all other available observations such as signs of instability (whumpfs, recent avalanching, shooting cracks), snow drifts etc.; to be combined with all other available observations (signs of instability, snowdrifts etc.).

Profile site selection

The criteria for selecting a profile site are as follows:

Safety first! → see safety procedures on front cover Slope

– Short, especially if avalanche situation is critical or unknown – Inclined as evenly as possible

– Avoid slopes with terrain traps

– Slope should not steepen downslope or end above cliff (hazard of falling)

Snowpack

– Select elevation band and aspects representative of the current avalanche problem, mostly shady slopes (NW-N-NE)

– Undisturbed snow cover with rather below-average snow depth – Steep slope (ideally with a slope angle of about 35°)

– Snow distribution as uniform as possible (→ check by probing) – Not close to ridges, cornices and bowls

– Snowpit wall in the shadow

(4)

2

n

q h x

n

q h x

Observer

Date / Time

Location

Elevation [m] / aspect / slope angle [°]

Coordinates

Weather (sky / wind / precipitation)

q = no. of meters of ram probe n = no. of blows of hammer h = drop height [cm]

x = total penetration depth [cm]

Snow profile

Profile location / snow surface / snow drift / alarm signs / avalanches / avalanche danger

Important information

Profile not to ground Total snow depth [cm]:

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(5)

3

H [cm] Θ F E R

Total snow depth

H = Depth (from ground) Θ = Liquid water content F = Grain shape E = Grain size R = Hand hardness

H [cm] Θ F E R

Stability tests and results Snow water equivalent

∆H [cm] ΔHW [mm] H [cm] Score and release type

(6)

4

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(7)

5

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(8)

6

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(9)

7

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(10)

8

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(11)

9

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(12)

10

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(13)

11

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(14)

12

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(15)

13

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(16)

14

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(17)

15

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(18)

16

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(19)

17

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(20)

18

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(21)

19

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(22)

20

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(23)

21

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(24)

22

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(25)

23

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(26)

24

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(27)

25

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(28)

26

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(29)

27

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(30)

28

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(31)

29

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(32)

30

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(33)

31

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(34)

32

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(35)

33

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(36)

34

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(37)

35

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(38)

36

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(39)

37

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(40)

38

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(41)

39

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(42)

40

n

q h x

n

q h x

Observer

Date / Time

Location

Coordinates

Snow profile

1 0 0 1 0 0

Temperature

H [cm] [°C]

Surface Air

(43)

41

H [cm] Θ F E R

Total snow depth

H [cm] Θ F E R

(44)

42

(45)

43

(46)

44

(47)

45

Rutschblock test (RB)

Procedure and score

A RB involves isolating a block of 2 m width (across-slope) and 1.5 m side length (up-slope). Front and side walls are dug with a shovel. The upper wall of the block is cut with a cutting cord.

The block fails:

1 while digging or cutting

2 while stepping onto the block with skis

3 while three times dropping from straight legs to bent knees 4 on first jump with skis from above

5 on second or third jump with skis from above 6 on first jump without skis from above 7 no release

Notation

The first number describes the score, the second number is the depth of the failure layer in the RB (the depth of the failure layer is measured from ground).

E.g. RB 04 @ 70 cm (the block failed on the first jump with skis from above at a depth of 70 cm). It is essential to record release type and fracture quality.

Release type Fracture quality

– whole block – smooth

– most of block (typically below skis) – rough – edge of block only – irregular

Snow profile (in shadow) Ram probe

Cutting cord

1.5 m

approx.

0.5 m approx.

0.5 m

Thermometer

2 m

(48)

46

Extended column test (ECT)

Procedure and score

An ECT involves isolating a column 90 cm wide (across-slope) and 30 cm side length (up-slope). Front and side walls are dug with a shovel. The upper wall of the ECT is cut with a cutting cord (or a saw). A shovel blade is placed on one end of the column and then progressively loaded by tapping on it until a failure initiates below the shovel.

Failure occurs:

01 – 10: while tapping ten times moving the hand from the wrist 11 – 20: while tapping ten times moving the forearm from the elbow 21 – 30: while tapping ten times moving the arm from the shoulder

Once a failure has crossed the entire column, the snow above the failure layer is removed. Otherwise the snow remains on the column. The test is continued on the remaining column until the next failure or the 30^th tap.

Notation

The first number describes the number of taps until a failure initiated e.g.

ECT 07 / XX @ 70 cm (the crack started on the 7^th tap moving the hand from the wrist at a depth of 70 cm; the depth of the failure layer is measured from ground).

For the 2^nd number (XX) there are three alternatives:

– The failure propagates across the entire column at a given number of taps, e.g.

ECT 07 / 08 @ 70 cm: the column fractures completely at the 8^th tap moving the hand from the wrist.

– The failure propagates but not across the entire column if tapping up to 30 times: ECT 07 / pp @ 70 cm (pp = partial propagation).

– The failure does not propagate beyond the area below the shovel blade: ECT 07 / np @ 70 cm (np = no propagation).

Special cases

– Column fractures while isolating the column, e.g. at a depth of 70 cm:

ECT 0 / 0 @ 70 cm

– No fracture (no failure initiation): ECT nf

Failure initiation:

– at which tap?

Propagation:

– Does the crack propagate across the entire column?

– At which tap?

90 cm 30 cm

(49)

47

Compression test (CT)

Procedure and score

A CT involves isolating a 30 cm by 30 cm column of snow. Front and side walls are cut with a saw and dug with a shovel. The upper wall of the CT is cut

with a saw. A shovel blade is placed on the surface of the column and then progressively loaded by tapping on it until failure.

Failure occurs:

01 – 10: while tapping ten times moving the hand from the wrist 11 – 20: while tapping ten times moving the forearm from the elbow 21 – 30: while tapping ten times moving the arm from the shoulder As soon as a fracture occurs, the snow above the fracture is removed

(see notation). The test is continued on the remaining column until the next failure or the 30^th tap.

Notation

The first number describes the number of taps until a layer fractures; the second number is the depth of the failure (the depth of the failure layer is measured from ground), e.g. CT 12 @ 70 cm (a layer failed on the 2^nd tap moving the forearm from the elbow at a depth of 70 cm). The fracture type should be recorded as follows:

– SP (sudden planar): The fracture is planar, sudden and the fractured part slides off easily*.

– SC (sudden collapse): The fracture appears suddenly and is accompanied by a visible settlement.

– RP (resistant planar): The fracture is planar, but it needs more than one tap until the fracture propagates across the entire column; or the fracture appears suddenly but the fractured part does not slide off.

– PC (progressive compression): The fracture occurs diffusely in a vertical region of one to several cm and the layer is further compressed by the following taps.

– B (non planar break): The fracture is irregular.

* The fractured part typically slides off on slopes steeper than 30°.

Fracture 30 cm 30 cm

(50)

48

Lemons (Red flags or threshold sum) Procedure

This method allows detecting possible weak layers without a stability test based on structural properties derived from the snow profile. The properties of layer interfaces and their adjacent layers are taken into account. The test score is automatically calculated in the Swiss snow profile software “Snowprofiler”.

Layer properties

Large grains (≥ 1 mm)

Soft layer (hand hardness index: 1, fist)

Persistent grain shapes: faceted crystals, depth hoar or surface hoar

Interface properties

Large difference in grain size across interface (≥ 1 mm)

Large difference in hand hardness index across interface (≥ 2 levels) Layer interface less than 1 m below the snow surface

Interpretation

(Number of lemons in a layer / at an interface) – 5 – 6 lemons: very likely a critical weakness

– 3 – 4 lemons: possibly a critical weakness

– 0 – 2 lemons: no distinct weak layer, rather favourable snowpack structure

Avalanche observations

Important observations

– Location (coordinates), time, elevation of start and runout zones, aspect, slope angle

– Avalanche size → see table on back cover

– Slab width and depth (measured vertically), length of the avalanche

– Slab, loose snow or glide-snow avalanche – Dry or wet (snow in starting zone)

– Natural or artificially triggered (person, explosives etc.), remotely triggered

– Failure layer within new snow or within a persistent weak layer

(51)

Symbol

(Code) Symbol

(1) (7)

(7–7 o crust)

(3) (8)

(5) (0)

Volume > 100 000 m³

Grain shape and typical sizes Avalanche sizes

Safety procedures

– Prepare field trip seriously and according to current conditions.

– Travel in a team of at least two; your partner also needs adequate experience and training.

– Check avalanche bulletin and weather forecast.

– Re-evaluate meteorological conditions, avalanche situation and your schedule regularly during the day. Adapt or cancel field trip if necessary.

– Carry safety equipment (avalanche beacon, shovel, probe; airbag recommended); wear the switched-on avalanche beacon directly on your body. Check transmit function of transceivers before start (Group check).

– Carry additional equipment if circumstances require (means of com munications and orientation as well as technical equipment).

– Approach profile site carefully one by one.

– Do not stay below the column during the rutschblock test.

– Fill all trenches after recording the profile.

– It is recommended to inform a contact person about the intended destination route and return time.

– Beginning of season: Check all safety equipment and practice how to use it.

Emergency telephone numbers

Switzerland

International

1 – 3 mm

(52)

Symbol

(Code) Symbol

(1) (7)

(7–7 o crust)

(3) (8)

(5) (0)

Volume > 100 000 m³

Grain shape and typical sizes Avalanche sizes

Safety procedures

– Prepare field trip seriously and according to current conditions.

– Travel in a team of at least two; your partner also needs adequate experience and training.

– Check avalanche bulletin and weather forecast.

– Re-evaluate meteorological conditions, avalanche situation and your schedule regularly during the day. Adapt or cancel field trip if necessary.

– Carry safety equipment (avalanche beacon, shovel, probe; airbag recommended); wear the switched-on avalanche beacon directly on your body. Check transmit function of transceivers before start (Group check).

– Carry additional equipment if circumstances require (means of com munications and orientation as well as technical equipment).

– Approach profile site carefully one by one.

– Do not stay below the column during the rutschblock test.

– Fill all trenches after recording the profile.

– It is recommended to inform a contact person about the intended destination route and return time.

– Beginning of season: Check all safety equipment and practice how to use it.

Emergency telephone numbers

Switzerland

International

1 – 3 mm

(53)

Liquid water content

Term Symbol Code

 2

 3

 4

Snow hardness

Very soft: fist 1

Hard: pencil  4

Ice  6

Temperature

Air temperature

Snow surface temperature

Snow temperature

References

Editors

Field book

for snow profile

observations

(54)

Liquid water content

Term Symbol Code

 2

 3

 4

Snow hardness

Very soft: fist 1

Hard: pencil  4

Ice  6

Temperature

Air temperature

Snow surface temperature

Snow temperature

References

Editors