Bollettino valanghe

San Francisco Peaks / Kachina Peaks Wilderness

Kachina Peaks Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Today, it is possible for a skier or rider to trigger a slab avalanche above treeline.  These avalanches are hard to impossible to predict and could be large in size.  Avoid steep and loaded areas at the top of avalanche paths and in starting zones, as these are the most likely areas to trigger this type of avalanche.   In near treeline and below treeline terrain, avalanches are unlikely.  

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    The December facets are still present in most areas under the snowpack, as is a weak layer associated with a single or multi-layered melt-freeze crust. In some locations, such as catchment zones and areas undisturbed by wind, this problem behaves as a deep persistent slab and has not been reactive to most stability tests.  However, in other locations, such as wind-effected chutes and gullies, this layer is buried a mere 50 cm or less in the snowpack and could be triggered by a single rider or skier.  Although unlikely, If triggered, these avalanches could be large and easily result in a complete burial.  Work around the top of avalanche paths guarded by large deposition zones and loaded starting zones.  These loaded starting zones and their margins, where the snowpack is thinner, are the most likely spots to trigger a large and dangerous avalanche.  

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–1.5

    Wind slab avalanches are unlikely, but skiers and riders should still avoid areas of wind-deposited snow, such as in cross-loaded gullies and in starting zones. Following a small transportation event Friday evening, winds died down and remained light throughout yesterday and last night.  A west wind is expected to increase again this afternoon.  The amount of snow available for transport above treeline is decreasing.   If triggered though, a wind slab could step down and impact the underlying weak layers. These conditions could produce large to very large avalanches (D2-D2.5 in size), and have destructive consequences.  Avoid heavily wind loaded zones, especially those at the top of steep avalanche paths, and be observant of any signs of instability, such as cracking or shearing.  

Avalanche Discussion

It has been over a week since the last snowfall, which resulted in our first and only avalanche cycle of the season. To view some of the aftermath and learn more about the size and type of these avalanches, click here.  Since then, the snowpack has become increasingly stable, and the avalanche hazard has decreased, but the danger level is not low in all locations.   A persistent slab avalanche could still be triggered on slopes where both basal facets and weak layers remain a problem.  Stability tests are less reliable with this type of avalanche problem, especially when the weak layers are buried deeper in the snowpack.  This problem might be dormant, but rising temperatures and the weight of a skier or rider could resurrect it.  

In most locations on the Peaks the persistent weak layers, some of which were failure points during the last storm cycle, were buried by over a meter of snow.  In areas that haven't slid, these weak layers are supporting the additional load, but this is in the absence of a skier or rider. Yesterday, a party on a north facing slope on north core ridge got an ECTPV result.  In locations of shallow snowpack where facets exist, the weight of a skier or rider will more highly affect the underlying layers, and could trigger a large avalanche.  In problematic locations, such as steep starting zones, we're still facing a low probability but high consequence scenario.  Avoid steep entries to avalanche paths, especially those that have been loaded or are actively being loaded by wind. 

In a few sampled locations, the temperature profile and crystal type, (rounding facets and rounds), suggest that this problem is starting to heal.  However, it may take a couple more weeks of warmer weather and possibly more snow before it completely abates.

Conditions on the Peaks are highly variable, and numerous aspects and elevations have been affected by both sun and wind.  Most mid-level elevations at nearly all, but south-facing aspects still contain soft snow.  Some south and west facing slopes are going through melt-freeze cycles, and as this warm weather trend continues, some slopes may start to corn up in the afternoon.  Much of the above treeline zone has been impacted by high winds and can boast a seriously slippery or grabby wind crust. The growing distribution of wind and sun crusts may be the future weak layers in the snowpack.

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