Case Studies

Shortly after completing his first avalanche consulting project in 1979, David Hamre (who was then the Snow Safety Director at Alyeska Resort) started having other consulting opportunities crop up. One of those was related to the “Alaska Pipeline.” Constructed and turned on in the late 1970s, the line was by then managed by Alyeska Pipeline Service Company (APSC). Notably, through Hamre’s several business names, the core of that consulting agreement continues in place more than 40 years later.

When the line began flowing, it pumped hot oil almost 800 miles from the barren Arctic near Deadhorse, Alaska, to the port and terminal in Valdez. Eight pump stations along the line pushed up to 2,000,000 barrels of oil per day through the line. Pump station 4 was installed in a position where it could push the hot oil up over the Brooks Range at Atigun Pass (elevation 4,800 feet).

The terrain at Atigun Pass is quite rugged. Although the line in the Arctic is primarily built onto Vertical Support Members (VSMs) and provided with a passive cooling system for keeping the permafrost frozen, this was not an option at Atigun Pass. The presence of considerable avalanche terrain forced APSC to bury the line. Given the presence of permafrost and gravity, by 1981, there were signs of severe stress in the line where it traversed the pass. It was determined that an engineered solution was desired to stabilize the pipe.

Options were outlined and included three basic choices, all of which were problematic.

1. Stabilize the line in place. This option required an array of engineered solutions to dissipate heat and provide stability to the line. This process’s outcome was unclear since a similar project had never been done.
2. Analyze the possibility of replacing the line with an above-ground alignment that would have appropriate protection against avalanche impacts.
3. Drill a tunnel through the mountain to place the line in.

At the time, David Hamre’s consulting company (the precursor to David Hamre and Associates, LLC) was asked to form a team to examine option #2 and determine its feasibility.

As the project manager, Hamre was tasked with choosing a team to do this analysis. He engaged several of the leading avalanche consultants of the time to assist with this analysis. They included:

• Dr. Ed LaChapelle -Preeminent avalanche scientist
• Art Mears, PE- Avalanche Engineer and dynamics specialist
• Dr. Larry Onesti- Authority on lichenometry in the Brooks Range
• Norm Wilson – Authority on avalanche mitigation options
• Phil Eastly – Avalanche Filmmaker

The project took 24 months to complete from start to finish. Most of the work completed was focused on conventional avalanche dynamics and resulting impact pressures. Analysis was provided for the whole line over the pass, documenting avalanche locations and impact pressures to a vertical wall. Dynamic forces were provided for this analysis.

The work above was not unique, but there was an element that had never been tackled before. This work entailed quantifying the potential effects of slush flow avalanches. This phenomenon is somewhat unique to the Arctic and potentially devastating to a pipeline in a slush flow path. While little was known by science at the time, there were people in the Arctic who had seen the results. The process began with interviews, cataloging potential slush flow runout zones, and working to determine the appropriate dynamics model to apply to these events since they are so unique. For example, whereas avalanches release in an angle range from 30-50 degrees or so, the steepest angle of a slush flow release measured was 15 degrees. Clearly, other dynamics were involved.

One of the biggest challenges of this whole project was the task of determining the frequency and magnitude of slush flow events. This, in turn, would drive the cost factors and any risk acceptance equations. Once the basics of slush flows and their dynamics were understood, the process of identifying the frequency/magnitude relationships in runout zones was undertaken. In the Arctic, slush flows, as a geomorphic process, produce unique landforms through the deposition of debris called “whalebacks.” Viewed in profile, they resemble the back of a whale as the flow exits a gully and leaves material. These “whalebacks” were thoroughly examined to determine the age of deposits based on lichenometry. This process assisted in understanding the geomorphology more thoroughly.

The information from this engineering process was internally published to APSC engineers as the four-part “Atigun Avalanche Engineering Study.” Parts 3 and 4 contain much original information about slush flows in general and an analysis of their potential effects on the “Alaska Pipeline” in particular.

This might have been the end of the story. The pathway chosen was to stabilize in place, which resulted in many avalanche risk reduction projects. But there is another element. Having listened to many papers describing the speed of avalanche fractures based on existing models, Hamre and Dr. Karl Birkeland published an alternative viewpoint in 2014, describing much higher fracture speeds that could not be explained by the modeling processes of the day. This paper served as a catalyst for Swiss scientist Dr. Johan Gaume to look into alternative models. From his work, he has developed a new model of avalanche fracture. Using computer animations run with the Material Point Method (MPM) championed originally by Disney for movies, Gaume can visually depict avalanche fractures from the new model with stunning, life-like accuracy. Hamre, Gaume, and Norwegian Geophysical Institute scientist and engineer Peter Gauer looked at the unpublished information on slush flows from the 1982 work and wrote a paper for the 2024 International Snow Science Workshop in Tromso, Norway.