Avalanche Assessment Data Sheet

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Assessment Date & Time: 18/07/2017 1221hrs
Observer Name/s: GK, CB
Assessment Location: Upper Otira Valley - True right flank (E1479272 N5248694)   Altitude (m): 1520m
Slope Angle (xº) & Aspect (1-360º Mag.): 35º, 300º

Current Weather Conditions: Fine weather.
Air Temperature (ºC): 7.4ºC
Wind Direction / Strength (1-360º Mag. / Kmph): 0º @ 0km/h
Hygrometer RH (%): 40% Falling
Uncorrected Barometer (mb): 934mb Stable

Previous Activity: Storm-cycle: Multiple Class 3 - 3.5 wet slab releases (40cm - 60cm) on eastern aspects from 1800m - 1900m, multiple Class 1 - 1.5 wet point releases out of lower altitudes on most aspects. Class 1-2 on Otira Slide (N).
Current Activity: Multiple Class 1-2 loose snow releases on solar aspect faces (Otira Faces) from 1100hrs. Class 1.5 out of "hidden gully" on Otira Slide.

Snow Crystal Descriptor Codes

Fresh snow Irregular grains, mostly rounded, but often branched. Early ET Rounded, often elongated. Isometric grains. Late ET. Angular grains with flat sides or faces. Early TG. Angular grains with stepped faces; at least some hollow cups. Advanced TG. Rounded grains formed by MF metamorphism. Graupel. Ice layer, lens, or pockets.

Hardness Descriptor Codes (Hand Test)

Very soft - Fist Soft - Four fingers Medium hard - One finger Very hard - Pencil Hard - Knife Ice - Impenetrable

Snow Structure Data

Surface10cm 20cm30cm40cm 50cm60cm70cm 80cm90cm100cm110cm120cm130cm
0.1ºC 0.2ºC 0ºC 0ºC 0ºC 0ºC 0ºC 0ºC 0ºC -0.1ºC 0.1ºC      
Layer Thickness
(Hand Test)
Size (mm)
1 6 MH 0.25 C Good No Shear 340 20mm Poor sintered bonds
2 4.0
VH 0.5 C Good No Shear 320 13mm Poor sintered bonds
3 5.0
S 0.5 C Poor No Shear 220 11mm Poor sintered bonds, free water present
4 20.0
VS 0.2 C Poor No Shear 296 59mm Poor sintered bonds, free water present
5 7.0
S 0.5 F Poor Easy 456 32mm Poor sintered bonds, free water present
6 2.0
MH 1.0 F Poor No Shear 460 9mm Poor sintered bonds, free water present, melt/freeze crust
7 4.0
VH 1.2 F Poor No Shear 420 17mm Poor sintered bonds, free water present
8 6.0
S 0.5-1.0 F Poor Easy 440 26mm Poor sintered bonds, free water present
9 12.0
MH 0.5-2.0 F Poor No Shear 440 53mm Poor sintered bonds, free water present
10 34.0
VH 0.5-1.0 F OK No Shear 446 152mm 0cm to rock, wet snow - sugary, free water present
Pack Statistics
Snowpack Depth: 100.0cm
Snowpack Weight: 392kg/sq.m

Pack Analysis :
Completely isothermic snow-pack in this location. Obviously affected by the heavy NW rain in the last storm-cycle (rain runnels galore). The entire pack was suspended by 2cm above the basal rock layer where water has eroded the snow away. Sintered bonds were poor throughout with free water is percolating down through the pack. A crust at 42cm is providing a glide surface for wet slab, as it is partially impermeable to water. Given more draining in next few days the various weaknesses will heal.

Shovel Shear Test :
Easy failures of the column at base of Layer 5 (42cm) and again at Layer 8 (54cm). Failure at 42cm on M/F crust (maybe rain crust), and 54cm on extremely loose and wet crystals.

Compression & Foot Pressure Tests :
42cm (layer 5) failed with moderate force in the compression test, this constitutes a wet-slab. Foot pressure test revealed a failure at about 54cm (layer 8), though this was right at edge of pit with moderate stomping.

Rutschblock Test :
Not performed.

Activity Assessment :
Low altitude presents good stability though avoidance of towering steep ground above would be prudent. Mid-altitude slopes have wet-slab present that could be reactive to skier/climber activity in areas exceeding 35º, or near edges and convex rolls. High altitude still has substantial loose wet snow (+ wind-slab) and presents a considerable hazard on solar aspects, this hazard has been rolling to valley floor under the steep faces. As the snow-pack drains the various weaknesses will heal, and quite hard ice slab should form.

Current Assessment :
High Alpine (2000m+) - Considerable
Alpine (1000m - 2000m) - Moderate
Sub-Alpine (Below 1000m) - Low

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