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Thread: Massive Turnagain Avalanche 1/8/13

  1. #1
    Member Erik in AK's Avatar
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    Jul 2006

    Default Massive Turnagain Avalanche 1/8/13

    On Tuesday, 8 Jan at about 4 pm a group of snowmachiners descending Seattle Ridge towards the parking lot triggered a massive avalanche on a face known as Repeat Offender.

    For reference, as you look up at Seattle Ridge this is the area immediately to the left (south) of the route snowmachiners take up and down Seattle Ridge. This slide was 700’ wide and 6' deep at the crown face (breaking point) and left a debris pile over 30’ deep. This slab released at the ground which is not typical of slab avalanches. From what’s been reported so far, fortunately, no one was killed or injured.

    This is the EXACT type of slide in the exact same spot that killed six riders in 1999.

    It's been an unusual winter in terms of snowfall--Little snow and lots of rain through the fall then two weeks of nearly continuous snow in places like the Chugach and Kenai mountains. Normally open riding spots like Placer River are slush and ice but just 1,500 higher the snow is neck deep on a giraffe. This snow pattern has created deep slab snow pack that has not been seen in decades. There WILL be more big slides this year.

    The mountain play areas are ticking bombs this year. Please ride smart.
    If cave men had been trophy hunters the Wooly Mammoth would be alive today

  2. #2
    Member Jimw's Avatar
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    Jul 2006


    ... i cut this from the avalanche center artical.....

    Seattle Ridge Snowmachiner Triggered Avalanche 4pm January 8, 2013


    Start Zone Elevation: 2500'
    Toe of Debris Elevation: 1,100'
    Vertical Fall of debris: 1,400'

    Crown Width: 1000'
    Crown Height/Depth: 2-8'

    Start Zone slope angles: 30-40 degrees avg

    East Aspect

    "Repeat Offender" aka snowmachine uptrack

    This avalanche was remotely triggered by a single snowmachine around, we think
    the 2200' elevation. Fortunately no one was caught, buried, injured or killed
    in this avalanche. The hazard was rated at CONSIDERABLE above treeline on this
    day, following a 15 day stretch of steady snowfall. The avalanche occurred as
    visibility was increasing towards the end of the day.

    A quick pit around 2200' in snow that had not slid revealed a total snow depth
    of 295cm. Roughly 30cm of 2mm faceted grains are intact at the bottom of the
    snowpack at this site. Our ability to affect this layer in a location like this
    is minimal at best. The distance from the snow surface to the weak layer is
    close to 9 feet.

    When areas of thinner slab are impacted, cracks are propagating long distances
    along these basal weak layers (see Tincan avalanche on 1/4 for another example
    of this). These layers are of varying thickness and are well developed. There
    are still many areas holding this basic set up of very strong thick snow over
    very weak snow. The likelihood of triggering these full depth avalanches may
    steadily decline but the consequences could be grim.

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