Assessment of Historic Avalanche on Going-to-the-Sun Road
May 15, 2009
Contact: Amy Vanderbilt
, 406 888-5838
WEST GLACIER, MONT. – A large-scale slab avalanche that slid 4,000 vertical feet from the Continental Divide across the west side of the Going-to-the-Sun Road (Sun Road) in Glacier National Park last January has caused much less damage than expected, park officials announced today. Park Superintendent Chas Cartwright remarked, “At this point, we see no reason why the entire Sun Road won’t open to vehicle traffic when plowing is completed… and when road and weather conditions permit the entire 50-mile long historic landmark roadway to open across Logan Pass.
At this time, nearly two thirds of the entire road is currently open for vehicles. Cartwright noted, “Springtime visitors to Glacier get a remarkable opportunity to walk portions of the Sun Road while vehicle traffic is restricted during spring plowing. This can be a great time to visit the park without the summertime traffic congestion."
“Fortunately, it appears that avalanche damage will NOT affect the opening of that portion of the Sun Road. At this time, we see no reason why this road damage would affect the opening of at least one lane through this section of the Sun Road.
The Class 5 avalanche was part of a series of avalanches that slid down and across the west side of the Sun Road in Glacier National Park most likely in January. A series of avalanches very likely covered lower elevation portions of the Sun Road, thus protecting the lower road from sustaining damage. The section of the Sun road that sustained avalanche damage was in the vicinity of Alder Creek, approximately two-and-one-half miles above The Loop.
The Class 5 slab avalanche most likely occurred on or about January 8, 2009. Heavy rain fell on top of a large accumulation of new snow. Avalanche specialists suggest that the heavy rainfall percolated through the snowpack, filtering down to the ground/snow interface. This caused an avalanche that started just below the Continental Divide along the Garden Wall and slid approximately 4, 000 vertical feet. The two slide paths crossed the upper Sun Road at Alder Creek and again near the Packer’s Roost road. This location was not previously identified as a known avalanche zone along the Sun Road.
According to park avalanche specialists, it is unlikely that an avalanche nearing this scale and magnitude has occurred for many decades.
Debris that consists of trees and rocks was deposited on the Packer’s Roost road at a depth of 15-20 feet deep. Spring plowing operations have included clearing the debris from both sections of the Sun Road and the Packer’s Roost road.
Park plowing crews only recently cleared snow from the upper roadway in the vicinity of Alder Creek. Once on site this week, National Park Service and Federal Highway Administration (FHWA) engineers have conducted an on-site preliminary damage assessment from this historic avalanche.
The NPS and FHWA engineers documented that the avalanche sheered away portions of stone masonry from the Sun Road at Alder Creek. Engineers confirmed that a 95-foot section of newly (2008) installed stone masonry wall was lost and approximately 450 feet of (1920s) historic stone masonry was removed by the avalanche. There is also approximately 200 feet of asphalt damage. According to Cartwright, “It is very unfortunate that we lost so much of the historic masonry wall, but given the scale of this avalanche, we are fortunate that damage to the Sun Road was not worse than it is. Ironically, the avalanche came through the current road rehabilitation zone where the roadbed has not yet been rehabilitation or damage.”
Managers will be assessing options for repairs that will include installing barrier rocks or other removable guardrails when the outer lane is repaired.
Editor’s Note: Photos of the avalanche path and debris clean up will soon be posted to the park’s web page “Spring 2009 Opening Photo Gallery.”