Preliminary Avalanche Accident Report         

Forest Service Utah Avalanche Center

 

Monday, December 30, 2008

 

Western Uintas – Yamaha Hill – 15 year old male snowmobiler caught, buried and killed in avalanche

 

History: Because of its long arduous approaches, snowmobilers are the predominate user group in the western Uinta Mountains. A grant from Utah State Parks and Recreation in the winter of 2003-04 allowed funding for a part-time weekend avalanche forecast program. Longer term funding was eventually established and now advisories are issued on the busiest days of the week- weekends and holidays with an additional midweek update on Wednesday. Since 2001, there have been eight avalanche fatalities involving seven snowmobilers and one skier, but each year there are many close calls that we never hear about.  

 

Location: The avalanche occurred low on the slope near a 36 degree breakover with a thin faceted snowpack.  (Click HERE for avalanche overview photo.) The location is known by Evanston locals as Yamaha Hill (Utah riders call it Avalanche Hill) in Moffit Basin.  (Click HERE for Google Map view.)

 

 

Accident and Rescue Summary: Details are still being sifted through, but what we know is this- a father and his three sons left the Bear River Service trailhead and rode their snowmobiles towards the Moffit Basin and ultimately landed near Yamaha Hill. Hayden Ellingford waited at the bottom of the slope as one of the riders from the group took a bite low on the slope above him, triggering a large avalanche. An organized outside rescue party found the man at approx. 17:54. He was not wearing a beacon nor did any members in his party have rescue equipment.

 

Avalanche Data: The avalanche averaged 4’ in depth, was 600’ feet wide, running for about 500’ vertically. Classified as a HS-AM-D2-R3-O/G. The avalanche failed on a thin layer of faceted snow above the Thanksgiving raincrust. (Click here for a simple snowpit profile)

 

Terrain: Yamaha Hill is a Northeast facing, open slope with very little vegetation in the main part of the bowl. The starting zone averages 32 degrees in steepness with several small mid slope breakovers measuring 36 degrees. The terrain is typical of many slopes in the western Uintas. Broad, flat windward ridges allow winds to transport a tremendous amount of snow even while it’s relatively calm in neighboring mountain ranges.

 

Weather and Snowpack History: The western Uinta snowpack is historically plagued by cold temperatures, shallow snow depths, very weak snow and strong winds… at face value, this year was no different. October was unusually dry and warm, though winter got rolling with an Election Day storm which deposited several feet of snow to the upper elevations. A warm, dry November followed rapidly settling total snow depths to about a foot. All south facing aspects shed their winter coat and reverted back to grass and bare rock. Two inches of snow fell on the evening of Friday November 29th.  However the bigger news was November went out with a bang of sorts. A moist, misty northwest flow moved into the region on the afternoon of November 30th and rain fell to the highest peaks forming an unusually stout raincrust which still plagues our snowpack.  

A colder northwest flow followed, ushering in December with a small storm depositing 3” of snow and strong ridgetop winds on Dec. 2nd followed by another quick hitting system on Dec. 8 with 8” of snow. Very strong prefrontal southwest winds raked the upper elevations on the evening of Dec. 12, gusting into the 70’s along the high ridges and peaks. Nearly a foot of light density snow fell overnight, overloading the fragile weak layers of the pack. The Dec. 13 advisory warned of the possibility of slabs breaking to the ground  on old layers of snow and test slopes confirmed our suspicions. Another 8” of snow fell on Dec. 16th.  An Avalanche Warning went into effect on the morning of Dec. 20 as new snow and hurricane force prefrontal winds continued to overload the structurally challenged snowpack. While the warning expired, a HIGH avalanche danger remained at the upper elevations, especially on north facing slopes that held snow during the November dry spell. A powerful Pacific system moved into the region on the 22nd depositing 16” of snow, followed by the Christmas storm which walloped the area with an additional 2’. Water totals were just over 2” in seven days. The Avalanche Warning remained in place through Dec. 27th and was downgraded to a Special Avalanche Advisory on the 28th. However, we strongly worded the advisory cluing people into the severity of the conditions and the consequences of triggering large, dangerous and possibly unsurvivable slides on slopes approaching 30 degrees in steepness.

 

Media Links:

http://www.ksl.com/index.php?nid=148&sid=5187644

http://www.sltrib.com/justice/ci_11332354

http://www.parkrecord.com/todaysheadlines/ci_11338199