Double Trouble

By Brad Carpenter

On March 31, 2020, a magnitude 6.5 earthquake violently shook south-central Idaho, in the U.S. Chris Lundy, a local ski guide in the Sawtooth Mountains near where the epicentre of the earthquake occurred, happened to be servicing the backcountry hut he co-owns there.

Lundy described what he experienced in his blog:

“At 5:52 PM, everything started to shake, rumble, and sway… Almost immediately we heard a different sort of rumbling—the kind that comes from large avalanches. My first thought was that a massive avalanche was about to hit the hut—an irrational thought since the yurts are in a safe location.”

The next day Lundy was amazed by what he saw in the surrounding mountains::

“April 1st dawned clear and cold, and at first light, we saw our first avalanches...The snow had slid from nearly every steep slope (see photo 1)…Slabs had fractured, powder had sluffed, and hanging snowfields had come unglued from vertical rock. The aprons below the steeper terrain were covered with piles upon piles ofavalanche debris.”

If there is enough snow on the ground and an earthquake occurs, avalanches can be triggered. The first time I experienced this fact was on September 4th, 201 0 when the magnitude 7.1 Darfield earthquake struck. This event caused extensive destruction to the Canterbury region resulting in billions of dollars of damage. The epicentre was located near enough to the surrounding mountains to cause a widespread earthquake induced avalanche cycle similar to what Lundy witnessed. There were multiple, large avalanche events triggered from steep terrain across the region.

Once I started looking into these dual-natural hazards I learned that there have been many such earthquake triggered avalanche events recorded in modern times:

A June 1 9, 1 994 avalanche at Porter Heights Ski Area was determined to have been triggered by an earthquake. The avalanche occurred at night, travelled downhill across a cat track and swept a grooming machine from the slope, tipping it upside down (see photo 2). The accident destroyed the grooming machine and fatally injured the groomer operator.

Photo 1: Earthquake triggered avalanches in the Sawtooth Mountains. Credit: Tanner Haskins, SMG.

In April of 201 5, a magnitude 7.8 earthquake in Nepal’s Himalayan Mountains triggered multiple large avalanches. Unfortunately one large avalanche swept through the Mount Everest Base Camp and killed at least 22 climbers and Sherpas.

Most recently an earthquake-induced avalanche event occurred in New Zealand on August 1 2, 201 9 in Fiordland National Park. A magnitude 5.5 earthquake, with its epicentre located 1 5km north of Milford Sound, occurred at 1 0:35 PM. Cameras located near the East Portal of the Homer Tunnel were able to capture images (see photos 3 and 4) of powder clouds emanating from two separate backcountry avalanche events triggered by the earthquake.

Although the science of avalanche forecasting has improved dramatically in modern times, at present there is no viable way to forecast for earthquake activity. As more people spend their time recreating and exploring in mountainous regions of the world the risk for human caused injuries or deaths from earthquake-induced avalanche events remains unchanged.

Thanks to: Milford Road Alliance, Sawtooth Mountain Guides. Mountain Safety Council,

Photo 3: An avalanche powder cloud drifts down McPherson. Photo courtesy ofMilford Road Alliance.

the valley from

Darfield 4 Sep. 2010; M7.1

Photo 4: An avalanche powder cloud drifts down the Gertrude Valley from Mt Talbot. Photo courtesy ofMilford Road Alliance.

Gisborne 20 Dec. 2007; M6.7

Kaikoura 14 Nov. 2016; M7.8

Christchurch Feb-Dec 2011; (M6.0 to M6.3)

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