All ice that falls is not an avalanche

Note: Updated with quotes from Patrick Wagnon, ICIMOD

On April 18, an avalanche on Mount Everest killed 16 Nepalese guides. By the end of the month, 13 bodies had been recovered. The search for the remaining three was called off after conditions were termed too risky and difficult. On April 22, the Sherpa guides announced they would not work on the mountain as a mark of respect for their fallen colleagues. The climbing season on Mt. Everest for 2014 was closed.

The incident drew attention from around the world – as consternation aimed at the Nepalese government’s provision of insufficient compensation and as concern over the effects of climate change. Its capacity to be a rallying point for anthropogenic warming was bolstered after another avalanche on May 23 that killed one climber and two more guides, who were scaling Yalung Kang, a sister peak of Mt. Kanchenjunga.

Except that the April-18 incident wasn’t an avalanche, according to some glaciologists, climate change specialists and other scientists from the International Centre for Integrated Mountain Development (ICIMOD), Nepal. They issued a ‘Clarification on  inaccurate media reports‘ on May 23, about a week after a conference on the Hindu Kush Himalayas cryosphere closed.

They attributed the April-18 tragedy to a serac fall, and explained how it was different from an avalanche.

“An avalanche requires a snowpack of sufficient depth with a weak layer, a sufficiently steep slope, and a trigger. In contrast, the 18 April tragedy on Mount Everest was the result of a different phenomenon called serac collapse. Seracs are large blocks of ice that are formed as a result of glacier fracture patterns and motion, and can fall or topple without warning.”

Thus, most of the time, there is no relationship between climate change and avalanche/serac risk.

Little to no link

According to Patrick Wagnon, one of the authors of the media clarification and a glaciologist at ICIMOD, “Serac falls are due to glacier flow and fracturation, and glaciers move down with gravity. Avalanche are due to snow falls, slope, and snow cover stability, and gravity is the main process to trigger avalanches.”

Going by the ICIMOD clarification, the April 18 avalanche that killed the 16 guides was triggered by a serac fall.

In the same statement, the scientists add, “Changes in the frequency of either avalanches or serac falls in the Everest region have not been definitively linked to climate change.” So further studies have to be done to establish the nature of the link between climate change and the frequency and magnitude of avalanches and serac falls.

Wagnon added, “As far as I know, no studies have been conducted so far to link climate change and serac falls or avalanches in the Himalayas, and very few in the Alps.”

However, Wagnon also cautioned that in some specific cases, glacier flow and associated serac fall can be modified by climate change. For an example, he referred to a case under study in the Mont Blanc area in France, where a serac barrier at 3,700 m, on the Taconnaz glacier, is dominating the town of Chamonix.

Such a glacier will be moving slowly because the its temperature keeps parts of it from melting. Since the amount of warming is sensitive to elevation, parts of glaciers at critical altitudes could warm up to close to 0° C and accelerate “from 1-10 m/year to 10-50 m/year”, precipitating a serac fall. On the Alps, the critical altitude above which the falls are likelier to happen is in the range of 3,500-3,900 m. On the Himalayas, around 6,000 m.

“But really, take care, it is in very few cases,” Wagnon concluded.

Not a glacial recession

At the end of the Himalayas cryosphere conference, ICIMOD published a report titled ‘Glacier status in Nepal and decadal change from 1980 to 2010 based on Landsat data (2014)‘. One of its conclusions is that the total glacier area decreased by 24% between 1977 and 2010, and, on average, glaciers were also found to be receding at 38 km2 per year.

Thus, the corresponding ice reserves had dwindled by around 129 km3 in the same period. The report’s authors note that while the impact of climate change on avalanches and serac falls is not fully known, rising local temperatures affect different physical features to different extents. As a result, they write, smaller glaciers that sport a larger surface area, those at lower elevations and with less-sloping surfaces are more pliant to warmer climes.

At the same time, the authors of the report advised caution in the clarification. Between 1980 and 1990, they speculate that the rate of ice loss could have been overestimated by the misclassification of snow as glacier ice – a characterization that’s yet to be fully understood.

(Hat-tip to Siddharth Varadarajan)