Avalanches on the Going-to-the-Sun Road

Introduction

For many of us, a new blanket of snow means hearing the swish of powder under our skis, or perhaps the makings of a perfect snowman. A snow-covered landscape brings a sense of quiet, stillness, and peace. But on a steep slope, under the right conditions, that seemingly benign layer can become something else. It can fracture like a pane of glass, creating an avalanche that roars downhill at speeds of up to 110 miles per hour. The immense weight and power of an avalanche can crush trees, cars, and people in its path. This power can be both devastating and rejuvenating—causing destruction and death, but also bringing new life to the landscape.

This slide, triggered with explosives, shows the power and speed of a large avalanche. An  Audio Described  version of this video is also available. Video: Courtesy Know Before You Go

The most familiar type of avalanches are known as dry slab avalanches. These occur in a cold, dry snowpack (one without meltwater) when a fracture line travels along a weak layer beneath the surface and releases a denser slab of snow above it. These types of slides are responsible for most fatalities, and they are studied intensively by snow scientists and avalanche forecasters across the West. Although predicting avalanche behavior is tricky, there is a well-developed understanding of the circumstances that lead to these events and the triggers that cause them.

Glacier National Park sees its fair share of these dry slab avalanches; natural slides occur throughout the winter, mostly without event. Some large ones deposit debris onto the Going-to-the-Sun Road (GTSR), leaving behind piles of dense snow. These drifts can be dozens of feet high and interspersed with trees and rocks, making them challenging for crews to clear in the spring. But for the most part, if backcountry users are not affected and infrastructure is not damaged, these avalanches go unnoticed.

Science

Impacts

While many of Glacier’s avalanches go unnoticed, their impacts do not. Avalanches greatly affect the landscape beneath the snow, which in turn changes how wildlife use those habitats. Many avalanches recur in the same starting areas and slide paths, sometimes annually and sometimes every century or more. A small slide may only shake the snow off a tree’s branches, but larger ones can strip the bark off of standing trees, or even take out whole swaths of forest. This results in vertical bands of treeless terrain, open for wildflowers, shrubs, and new trees to colonize. This open habitat also provides huckleberries for grizzly bears to eat, and new shoots and forage for a variety of species like mountain goats and bighorn sheep. Slide paths can even act as a firebreak, under some conditions. These periodic disturbances provide a mosaic of habitats along mountain slopes, increasing diversity among wildlife and vegetation species.

Left: Avalanche paths are slow to melt out in spring and early summer, leaving piles of snow late into the season. Right: By mid-summer these paths melt out, revealing downed trees and new, immature regrowth. NPS photos

Plowing

Every April, Glacier National Park road crews begin the daunting task of clearing the still-significant winter snow drifts off the Going-to-the-Sun Road. This historic landmark crosses the continental divide at Logan Pass (6,646’), connecting the east and west sides of the park. The road is closed every winter due to heavy snowfall, strong winds, and avalanche hazards; even by June, it is not uncommon to find ten feet of snow at Logan Pass. While the park and lower portions of the GTSR remain open in the winter, opening the alpine section of the GTSR in the spring is a priority due to its popularity and high tourism value.

Left: Hazards are present even on flat sections of road, such as the swift, icy creek. Right: Avalanche debris is often filled with trees and rocks, which can pose problems well into spring plowing. NPS Photo/W. Muelhlof

Crews start at Lake McDonald Lodge on the west side of the park and St. Mary on the east side, clearing any remaining snow on these flat, low-elevation sections of road. Yet even these areas can pose hazards. Many miles of road follow the steep banks of rivers and lakes, making work precarious. Debris piles left by winter avalanches can also slow progress in these areas. Not only do slides leave tall drifts of snow behind, but the paths can also contain trees and rocks, which must be removed before plows can get through.

Explore the Going-to-the-Sun Road's avalanche paths in this interactive map. The paths are colored by the length of road that they impact (red affects the longest segment of road). Note to mobile users: interactive features may be limited. For the best experience, view on a desktop computer.

As crews climb higher on the road, into steeper, alpine terrain, conditions become more hazardous. Stakes are at their highest on the 14 miles of road between Packers Roost and Siyeh Bend, referred to as the alpine section. The road traverses through dozens of avalanche paths—some of these slides occur each year in the same confined areas, but others are spread over long sections of road, making it difficult to mitigate these hazards. Historically, as well as today, spotters are positioned at locations where they can watch avalanche start zones and warn crews working below if a slide starts. Unfortunately, this is less effective on foggy or stormy days, or for larger slides that can travel quickly downslope. The work also doesn’t end with snow removal; every year, crews have to repair damage to the rock walls caused by larger avalanches and reinstall the hundreds of wooden guardrails that are removed each winter to prevent slide damage.

A small excavator sits on a snow-covered, narrow alpine road beneath a large, rock wall.

An excavator carefully removes snow from a precarious section of the Going-to-the-Sun Road, one bucketful at a time. NPS photo

1953 Avalanche

Road crews make safety a priority, but it’s hard to be completely safe while working in avalanche terrain. Even so, only a few accidents have ever involved the plow operators, and only one resulted in fatalities. On May 26, 1953, crews cleared past the Loop on the west side of the GTSR, but the remaining miles of snow-filled road made the desired mid-June opening unlikely. Not helping matters, a warm, maritime storm system passed through Glacier, depositing rain at lower elevations and up to two feet of wet snow at higher elevations. As the storm cleared, a team of four park employees drove up the road to assess the storm-generated slides, hoping to resume the snow removal process. A spotter kept an eye on the slopes high above them while the rest of the team worked on a slide path at Haystack Creek. Without warning, the weight of the wet snow above them triggered a new slide, but from an adjacent lower slope, much closer to the crew and out of the spotter’s sight. As the avalanche approached, one man jumped into a previously plowed cut on the road and was buried. The other three were swept down the mountain.

Left: Rangers on scene at the 1953 avalanche accident communicate via radio with park headquarters. Right: Rescuers search for victims in the debris. Jean Sullivan was found near the center of the photo. Photos courtesy of Glacier National Park Archives

A half hour later, a foreman came to check on the group’s progress. He found a fresh slide, an empty truck, and no crew. Piecing together what happened, he radioed park headquarters for help. Ninety minutes after the avalanche, rescuers found one employee partially buried, about 500 feet below the road. He was severely injured and unconscious, but they were able to wake him and bring him to safety. Another man who had been operating a plow at the time was found almost completely buried. Though rescuers uncovered him, he sustained severe trauma during the slide and did not survive. As hours passed, hope dwindled. But miraculously, seven and a half hours after the accident, a fellow road crew member probed and dug through eight feet of snow to discover Jean Sullivan, the man who took shelter in the plow cut. He was alive. The crew’s foreman was not found until dawn the next day, when a Bitterroot Valley man and his bloodhound arrived on scene to help with the search; he too had died of trauma during the avalanche.

Left: Jean Sullivan, seated, recuperating after his ordeal. Dimon Apgar, who located Jean, stands next to him. Right: George Talbot and his bloodhound, Joy, came from the Bitterroot Valley to assist in the search. Photos courtesy of Glacier National Park Archives


By mid-May, staff are bombarded with frequent questions regarding the GTSR’s opening date. The road generally opens fully in mid-June, but it has opened as early as May 16 and as late as July 13. Many people try to guess the opening date based on how snowy the winter was, but that’s not actually the most reliable predictor. Spring weather remains the biggest influence on the road’s opening date. On low-visibility days, spotters can’t get a clear view of avalanche start zones to warn plow operators about slides, making work much more hazardous. Rain falling onto an already wet snowpack can also heighten avalanche danger, forcing crews to pause or stop work altogether.

Brian Paul, a road crew supervisor, discusses the factors that influence when the road opens each year. An Audio Described version of this video is also available.

Forecasting

U.S. Geological Survey (USGS) and National Park Service (NPS) avalanche forecasters stationed in the park produce a bulletin each morning describing the conditions and specific hazards of the day. Depending on the day’s predicted weather, as well as the weather and snow conditions of the past several days, road crew leaders can make informed decisions. For example, crews can proceed as normal; they can cancel plowing operations for the day; schedule work to conclude before avalanche danger increases as temperatures warm; use safe zones along the road to minimize time spent in slide paths; or some combination of the above. No perfect formula exists for avalanche forecasting or decision-making, other than waiting until August for the snow to melt. Short of this, USGS scientists and park road supervisors collaborate to ensure that crews can clear the road in the safest conditions possible.

Left: Spotters watch avalanche start zones above the road so they can warn equipment operators of a potential slide. Right: Many high-hazard areas of the road pass directly through avalanche paths. NPS photos

Avalanches are often perceived as a winter hazard, but they can occur late into the spring, as long as there remains a deep enough snowpack and a steep slope. However, slides that occur in winter, when the snowpack is typically drier, are fundamentally different from slides that occur in the spring, which generally consist of snow saturated with meltwater.

As temperatures rise and days lengthen, upper layers of snow start to melt, draining into the snowpack beneath. As long as this melting isn’t too rapid, the water will gradually move through the snowpack, forming drainage channels within the snow. But when changes are too rapid, snow starts to become unstable. If temperatures become so warm that the upper layers of snow melt quickly, that rush of water can overwhelm drainage channels. Instead of draining neatly, the water will saturate any weak layers and flow horizontally and downhill along them, dissolving the bonds between the grains. When this weak layer cannot support the weight of the snow above it, it slips, and the whole slab moves downhill. This is known as a wet slab avalanche.

A column of packed snow is stained brown in the center. Above cracks in the snow, the stain extends horizontally.

This demonstration uses cold coffee to show the drainage of liquid through a wet snowpack. Instead of moving evenly down through the snow, it pools above crusts in the snowpack and spreads horizontally, breaking down the bonds between crystals. If this behavior is widespread, it can cause a wet slab avalanche. Image courtesy of American Avalanche Institute; Drew Hardesty

Background image shows a recent avalanche slide on top of a snowy mountain.

Glacier National Park's Brian Paul and U.S. Geological Survey's Erich Peitzsch explain how using science to forecast avalanche conditions on the Going-to-the-Sun Road increases the safety of the park's road crews during spring opening. An  Audio Described  version of this video is also available.

Climate

As the Earth’s climate continues to warm, changes in temperature and precipitation patterns impact northwest Montana’s snow depth, seasonal timing, and avalanche dynamics. One research project currently being conducted by USGS scientists involves looking at the frequency and size of major avalanche cycles in the past, in order to identify changes that might occur in the future.

Peitzsch and his colleagues study scars found on trees that have been hit with passing avalanches. In the same way that tree rings record drought and fire, they also record avalanches with scarring or “reaction wood”. Scars form when a slide rips off bark or gouges the trunk with debris. Reaction wood forms when a tree is bent downhill by the slide, then grows slightly asymmetrically to right itself. Both can be recognized in the tree’s rings, and scientists can date when those events happened by counting and dating the tree’s rings and identifying those markers. Researchers are visiting slide paths in several areas in the park and surrounding area to establish a regional avalanche chronology.

Erich Peitzsch discusses his research on the links between major avalanche years and climate patterns. An  Audio Described  version of this video is also available.

Once Peitzsch possess a clearer understanding of the size and frequency of past avalanches, he will have a benchmark to look at how changing patterns of weather and climate will affect future slide activity. This is a complex problem because simpler variables, like temperature and snowfall, don’t have a one-to-one correlation with avalanches. For example, more snowfall doesn’t necessarily mean more slides, nor do warmer temperatures. Instead, the key to causing avalanches lies in the formation of a weak layer, followed by plenty of snow falling on top of it. In northwest Montana, those weak layers often form when there is a long cold snap, turning the top of the snowpack into weak facets, which are crystals that support little weight and do not bond well with other snow layers.

Glacier National Park frequently receives warm, moisture-laden Pacific storms—if one arrives after a cold snap and stacks a foot or more of wet, heavy snow on top of a weak layer, then conditions are ripe for large avalanches. With climate change, weather is becoming more volatile. Winter storms that dump numerous feet of snow in a short period, or that are warm enough to deposit rain on existing snow, will become more common, stressing the snowpack beneath and increasing the likelihood of large avalanche cycles. Spring conditions are also arriving earlier each year, creating warmer temperatures and wetter, heavier snow—lengthening the time frame when wet avalanches can occur.

A high alpine lake surrounded by mountains glistens in the sun.

Hidden Lake is accessed by a short hike from Logan Pass, the high point of the Going-to-the-Sun Road. The lake sits at 6,375' above sea level. NPS photo

For the many people who are unable to or don’t want to hike several rugged miles uphill, the Going-to-the-Sun Road may be the only place within Glacier National Park they will ever experience the alpine. Each day during the summer, thousands of visitors pass through the park’s west entrance, many of whom stop at Logan Pass, the GTSR’s highest point. With its expansive views, access to pristine trails, flower-covered meadows, and rugged peaks, the GTSR is a must-see. The road is also a major factor in attracting visitors to the region; a study conducted in 2003 indicates that tourists contribute over $200 million annually to the local economy. With the total number of park visitors rising to over three million per year, most of whom will drive the GTSR, the iconic nature of this historic roadway is apparent—and significant time and money are expended to care for it.

As visitation increases, so does pressure to open the Going-to-the-Sun Road as soon as possible each year. Yet, as the climate continues to warm, unknown elements are added to the already difficult job of avalanche forecasting. Scientists predict more frequent rain-on-snow events, which is a prime cause of winter avalanches, as well as an increase in warm days and earlier springs, extending the period when wet slides occur. Researchers are also studying whether the overall size and frequency of avalanches may change, which could have impacts for the wildlife that rely on these paths for food and shelter. With continued research and collaboration among USGS scientists and Glacier National Park staff, we will have a better understanding of these natural phenomena, keeping park road crews safe and opening the road so visitors can experience these wild places.

Crown of the Continent Research Learning Center — Glacier National Park

StoryMap developed by Peri Sasnett and edited by Melissa Sladek

Additional Footage and Photographs provided by Glacier National Park and U.S. Geological Survey

An excavator carefully removes snow from a precarious section of the Going-to-the-Sun Road, one bucketful at a time. NPS photo

This demonstration uses cold coffee to show the drainage of liquid through a wet snowpack. Instead of moving evenly down through the snow, it pools above crusts in the snowpack and spreads horizontally, breaking down the bonds between crystals. If this behavior is widespread, it can cause a wet slab avalanche. Image courtesy of American Avalanche Institute; Drew Hardesty

Hidden Lake is accessed by a short hike from Logan Pass, the high point of the Going-to-the-Sun Road. The lake sits at 6,375' above sea level. NPS photo