Avalanche Assessment (local)

Click Here for current MSC Arthur's Pass Avalanche Assessment

Assessment Date & Time: 22/08/2023 1130hrs
Observer Name/s: GK, CB, VL
Assessment Location: Upper Otira Valley
GPS Coords: E1479238 N5248650
Altitude (m): 1554m
Slope Angle (xº) & Aspect (1-360º Mag.): 33º, 270º
Site Weather Conditions: Clear skies, no wind, warm
Air Temperature (ºC): 3.9ºC
Wind Direction / Strength (1-360º Mag. / Kmph): 0º @ 0km/h
Hygrometer RH (%): 28% Falling
Uncorrected Barometer (mb): 1023mb Rising
Previous Activity: Class 2 + 3 wet snow from altitude, either face deload events or slab (crown = 0.5m).
Current Activity: Minor wet snow slides off steep faces in sun. Some minor snowball activity on radiated slopes 40º+.

Snow Crystal Descriptor Codes

ABCDEFGHI
New snow Partly decomposed snow Small rounds Faceted grains Rounding facets Melt freeze crust Graupel Ice layer Needles
JKLMNOPQR
Columns Plates Melt freeze/wet Clustered grains Polycrystals Slush Rounded grains Depth hoar Surface hoar

Hardness Descriptor Codes (Hand Test)

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

Snow Structure Data

Temp
Gradient
Surface10cm 20cm30cm40cm 50cm60cm70cm 80cm90cm100cm110cm120cm130cm
0.2ºC 0.5ºC 0.2ºC 0.2ºC 0.1ºC 0.1ºC 0.1ºC 0.1ºC 0.1ºC 0.1ºC 0ºC 0ºC 0ºC 0.1ºC
140cm150cm 160cm170cm180cm 190cm200cm210cm 220cm230cm240cm250cm260cm270cm
0.1ºC 0.1ºC 0.1ºC 0.1ºC 0.1ºC 0.1ºC 0.1ºC 0.1ºC 0.1ºC          

Layer Thickness
cm
(base)
Hardness
(Hand Test)
Xtal.
Size (mm)
Xtal.
Shape
Internal
Bond
Column
Shear
Force
ECT
Shear
Force
Density
kg/m3
Water
Equiv.
Notes
1 10 S 0.5 F OK 440 44mm  
2 8
(18.0)
S 1.0 P OK 460 37mm  
3 12
(30.0)
S 0.5 P OK 480 58mm  
4 4
(34.0)
VS 0.7 P Poor 400 16mm  
5 2
(36.0)
VS 0.5-1.0 P Poor CT0 400 8mm Poor sintered bonds
6 14
(50.0)
VS 0.2 P Poor 360 50mm  
7 12
(62.0)
S 0.5 P OK 420 50mm  
8 5
(67.0)
S 1.0 P Poor 400 20mm Free water present
9 12
(79.0)
MH 0.2 P OK 400 48mm  
10 11
(90.0)
MH 0.5 P OK 420 46mm Some free water present
11 8
(98.0)
H 1.5 P OK CT11 480 38mm Poor sintered bonds
12 13
(111.0)
S 1.0 P Poor 400 52mm  
13 15
(126.0)
H 2.0 P OK 520 78mm Good sintered bonds
14 4
(130.0)
H 2.0-3.0 P OK CT0 520 21mm Wet snow - sugary, no sintered bonds, free water present
15 12
(142.0)
MH 2.5 P Poor 540 65mm  
16 14
(156.0)
S 1.0-1.5 P Poor CT0 520 73mm Wet snow - sugary
17 11
(167.0)
MH 1.0 P Poor 545 60mm  
18 13
(180.0)
MH 0.5 P Poor 500 65mm  
19 30
(210.0)
VH 1.5 P Poor CT0 540 162mm Wet snow - sugary, no sintered bonds
20 10
(220.0)
VH 1.0-3.0 P Poor 540 54mm Wet snow - sugary, no sintered bonds

Pack Statistics

Snowpack Depth: 220.0cm
Snowpack Weight: 1045kg/sq.m

Pack Analysis

Pack is completely isothermic, and very wet / heavy. Snowpack is not homogeneous, having 20 distinct layers identified over the 2.2m depth to ground (rock). Rain water has penetrated pack to depth and destroyed the sintered bonds throughout the pack. The pack in this test location is only 50% of normal depth for winter at this time. Pack would be stable in uniform surface areas, but prone to wet slab failure near edges or pronounced rolls. There is evidence of windslab (50cm) on S aspects (1700m+).

Column Shear Test :
5 shears identified in pit column. The 36cm & 100cm shears wewre expected from xtal analysis. The further 3 easy shears below were not expected, but xtal interface obs revealed very poor inter-layer bonds at these points.

Extended Column Shear Test :
Not performed.

Foot Pressure Tests :
1st test - 30cm surface slab released with moderate foot pressure about 0.5m back from pit edge. 2nd test - 40cm surface slab released with moderate pressure about 0.5m from pit edge. 3rd test - 100cm surface slab released with strong pressure exerted on pack about 0.5m from pit edge.

Rutschblock Test :
Not performed, no skis.

Activity Assessment :
Rising freezing levels, and intense solar radiation is likely to drive a cycle of wet snow events out of steep terrain features, there is potential for these to amplify should they pass through more uniform terrain creating very wet/heavy run-outs. A 50cm slab feature is visible on southern aspects 1700m+, this is likely to persist! Lower altitude snowpack is crusting up with M/F cycles, but remains extremely wet.

Current Assessment

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



Page updated 24/09/2024

© arthurspass.com 2024