1/21/2010 10:43:00 AM
by Meadows Team
in Connection, Media Center
| 19 comments
In the early evening of Sunday, January 17, a hard slab avalanche approximately ¾ of a mile wide near the top of the Wy’East face at the 10,650 foot level on Mt. Hood fractured and slid. The “crown” or fracture line ranged in depth from approximately four to ten feet and the incident triggered slides into three different watersheds – White River Canyon (between Meadows and Timberline), Newton Canyon (to the North of our permit area) and most significantly Clark Canyon, just inside our permit area.
The avalanche continued down the Clark Canyon drainage depositing itself in the foothills area about 200 yards shy of the Heather Chair Lift. In total it traveled 2.75 miles, collecting several thousand tons of snow, ice and debris before exhausting itself. The pile of ice, snow, rubble and debris in the deposition zone ranging in height from 15 to 30 feet.
The Hard Slab avalanche released naturally on an old crust that was formed just over a week prior. This event occurred above our permit area where no avalanche hazard reduction occurs. The conditions leading to this natural release were a hard ice layer formed from rain then a melt freeze cycle. This was followed by a storm cycle that deposited five to ten feet of wind loaded snow on top of this layer, including the moderate precipitation on Sunday.
The course and debris entered the ski area at the most remote part of our permit area, and at a time the terrain was closed. No guests, staff members or physical property was involved in this incident.
Avalanche Info
Avalanche starting zones generally occur on slopes between 30 and 60 degrees. They can run, and even accelerate, at pitches between 15 and 30 degrees especially when confined, such as the terrain in Clark Canyon. When the slopes hit 15 degrees or less the avalanche will generally decelerate to a stop, leaving huge amounts of debris in the deposition zone.
In terms of size, avalanches are measured on “R = Relative size to path” and “D = Destructive Force” scales –from 1 to 5, 5 being the largest and most destructive. Sunday’s avalanche was classified “R4” and “D4”.
Sunday's Avalanche Stats:
- Slope distance travelled: 14,500 feet, 6,000 meters or about 2.75 miles from start to finish.
- Elevation lost: 5,400 feet from the crown at around the 10,650 foot level to the “toe” at the 5,240 foot level.
- Width of the starting zone: 3/4 mile wide.
- Crown height at the fracture: Ranging from 4 to 10 feet
- Deposition field is in the millions of cubic feet of debris with up to 15 to 30 foot depths.
Sunday’s avalanche is not as uncommon as originally reported. Since 1976 there have been 23 naturally occurring avalanches, R4 or bigger, in the Heather Canyon drainage. During this same time period, there have been 16 R4 or bigger events in the Clark Canyon drainage. The majority of these larger natural slides, in the Heather drainage, occurred prior to 2002. Since that time patrol has increased the frequency and effectiveness of avalanche hazard reduction in Heather Canyon. This has greatly reduced the number of large, natural avalanches in Heather Canyon. However, current reduction measures for Clark Canyon are a challenge because some of the larger start zones are above our permit area.
This file photo taken from Super Bowl gives some persective and a "lay of the land" view of Clark and Heather Canyons. You can see the remnants of an avalanche track in Clark which is the more natural path of avalanches which start above our permit area.
Fortunately no guests, staff members or physical property was involved in Sunday's avalanche. This is an awesome display of nature that we respect, admire and learn from.
Coincidentally, January 16 – 22 is National Ski Area Safety Awareness Week. It is appropriate to focus on rule #6 of the Responsibility Code:
Observe all posted signs and warnings. Keep off closed trails and out of closed areas.
There are times that we close the gates to Heather Canyon, or portions of Heather Canyon, because of these conditions. We ask you to respect those boundaries, and never cross a rope line. The consequences can be deadly.
When heading into any of our gated access terrain – Heather Canyon, Clark Canyon, Private Reserve and Search & Rescue Cliffs, we highly recommend Skiing/Riding with a partner and carrying a beacon, probe, and shovel.
Enjoy the pictures – and let them serve as a reminder of just how awesome the nature of our mountain is. The pictures were taken by Executive Director of Mountain Operations Steve Warila, and Tighe Stoyanoff Head of Snow Safety. Thanks to Tighe and Nicholi Stoyanoff - Snow Safety, Patrol Director Melissa Toney and Patrol Manager Brandon Backman for their assistance in presenting this blog.
Also - kudos to our snow safety, patrol and grooming departments who were able to reopen lower Heather Monday before noon. Our groomers moved a lot of snow to create access back to the Heather Chair for our guests.
The crown or fracture line is right at the top of the Wy'East face. The majority of the slab and debris slid down and was collected into Clark Canyon, typical of these slides which start above our permit area.
From Accordian Bowl, a patroller views the track leading to the deposition zone just before the cut off to the Heather chair ramp.
Working down off the flats below Accordion Bowl, encountering debris along the edge of the track left by the avalanche as it rounded a corner. An R5 may have taken those trees out as well.
Notice the gouging of the earth by the avalanche as it passed through the flats of Accordion - the berm is between 25 and 30 feet high indicating the height of the avalanche at that point.
Measuring a five foot tall ice boulder with a rock encased in it.
The Avalanche created this 25+ foot high berm or side cut as it smashed into the side of the canyon and altered course.
The berm is still pronounced and you can just barely make out the ramp up to the Heather Chair beyond the debris, which is almost impossible to ski through once it sets up into varying sized ice and snow clumps. The deposition zone ranged in depth from 15 to 30 feet.
Looking back at the deposition zone from the ramp leading to the Heather Chair you can see the massive depth on the right hand side – that’s a 20 foot tall tree the snow is pushing over.