Bonnington Range Observations

Riding quality was:

Amazing

Snow conditions were:

• Crusty
• Deep powder
• Powder
• Wind affected

We rode:

• Dense trees
• Mellow slopes
• Open trees

We stayed away from:

• Alpine slopes
• Convex slopes
• Steep slopes

The day was:

• Stormy
• Windy

Avalanche conditions

• Slab avalanches today or yesterday.
• 30cm + of new snow, or significant drifting, or rain in the last 48 hours.
• Whumpfing or drum-like sounds or shooting cracks.
• Rapid temperature rise to near or above 0°C or wet surface snow.

We observed the new years avi cycle from Steed hut in the Bonnington range Dec 29 - Jan 2. Terrain is 1900m - 2300m, on mostly S to E aspect alpine slopes and N/E/S slopes at treeline. We didn't see much evidence of the alpine slopes failing during the previous large storm so avoided all big terrain.

Dec 29 was clear and warm with boot top powder above a supportive crust. Pits revealed a complex snow pack consistent with the forecast with moderate compression test results in the upper snowpack with columns often failing on the base facets once separated. Above the base facets we found 2 very dense 1 - 2cm ice crusts separated by ~2 cm of faceted lower density snow. Spooky. Warm Temps and strong sun resulted in a surface crust on solar aspects which overnight and Dec 30 grew surface hoar up to 10mm.

Overnight snow and strong wind Dec 30 resulted in a natural cycle Dec 31 to size 1.5 in the storm snow. Wind slabs were easily cut from the ridge tops and when visibility improved could be seen failing naturally on many wind affected treeline slopes at convexities on marble mountain.

Further overnight snow and gusting wind finally tipped the scale resulting in widespread natural releases to size 3, presumably starting late Dec 31 and overnight into Jan 1. For example Jan 1 we controlled released a N aspect wind slab at treeline from ridge top with a crown ~150m long which ran up the ridge from where it started. Pits in sheltered treed terrain were failing on the hoar frost/sun crust with a single tap.

Clear skies Jan 2 revealed evidence of the cycle. Days of wind transported snow had obscured the crowns and debris but much of Siwash Mountain's east bowl appears to have released windslabs below the cornices with a total crown of perhaps 300m - 400m with debris piles visible in the upper bowl and bottom. It looked as if the slide may have stepped down to the base facets at one point below the peak revealing the talus field but hard to be sure. Most big slide paths we saw shed the recent storm snow and did appear to be stepping down in places with heavy loading of debris but not to the ground.

The attached cell phone photos are hard to make out after so much drifted snow and my observations may be incorrect but it appears that this zone still has the persistent weak layers intact and active despite the recent cycle in the storm snow and I'd expect them to remain reactive with incoming storms.