The Caucasus Mountains, which stretch across southern Russia from the Caspian Sea westward to the Black Sea, are home to some of the highest peaks in the world — Mount Elbrus, at 18,510 feet (5,642 meters), is the highest mountain in Europe.
The rugged, isolated mountain range is getting international attention this week, as the world's gaze turns to the 2014 Winter Olympics, held in Sochi on the western edge of the Caucasus range.
But since 2008 (when Sochi was selected as the Olympic host city), the jagged peaks and rocky slopes of the Caucasus Mountains have been scrutinized by scientists because of one other feature of the range: Its unique combination of climate and topography has caused some of the deadliest avalanches in recent history. [Odd Olympics: 6 Unlikely Competitors at the Sochi Games]
An 'extraordinary' event
On the evening of Sept. 20, 2002, a fast-moving avalanche of rock and ice killed 140 people, smashed dozens of homes and businesses, wiped out roads and obliterated other infrastructure on the northern face of the Caucasus Mountains near the Kolka Glacier.
Researchers writing in the journal Natural Hazards and Earth System Sciences noted that, although such rock-ice avalanches aren't uncommon, "several aspects of the Kolka event are, however, extraordinary, among them the extreme acceleration of the avalanche mass on a moderately inclined slope, the high flow velocity, the long travel distance and particularly the almost complete erosion of a valley-type glacier. The Kolka avalanche is, furthermore, the largest historically documented ice avalanche so far."
In 2010, another avalanche in the Caucasus region killed five mountaineers, according to the BBC. The following year, a massive avalanche near the village of Ansokh buried four people: After an extensive search involving some 400 rescuers, all four were eventually found alive, but three of the men had been buried under snow and ice for several hours before being rescued.
Sochi: perfect avalanche conditions
What makes the Caucasus Mountains the site of so many deadly avalanches? After Sochi was selected as the site of this year's Winter Olympics, researchers and risk-management engineers were tasked with taking a closer look at the region, which, because of its isolation and lack of development, had been little-studied.
In an analysis presented at the 2012 International Snow Science Workshop, the researchers reported that the area's climate and its location near the Black Sea play a major role in avalanche occurrence.
"The climate results from the interplay of cold air from the north with moist, warm air from the Black Sea," the authors wrote. As a result, "the precipitation sums are huge," and can be as much as 3.3 feet (1 m) of snow in a 24-hour period.
Additionally, the highest slopes surrounding Sochi are particularly steep. "In Ober Khutor or East Bowl [ski area], where many bowls overhang long, steep slopes, huge avalanches are possible," the researchers wrote, "entraining large snow volumes able to reach the lower altitudes and especially the Rosa Lake plateau above the Olympic races finish zone."
Finally, because of the relatively mild temperatures in much of the Sochi region, snowfall often rests on unfrozen ground. "This fact, in combination with the heavy snow climate, promotes snow gliding," the researchers wrote, referring to the movement of large masses of snow. "It occurs on slopes steeper than 25 degrees, particularly when the ground is warm and the vegetation not very high or [conducive] to slippery interface." [Sochi Winter Olympics Sites Seen From Space]
How to stop an avalanche
Olympic planners are addressing the potential for avalanches with what is literally an arsenal of tactics. Despite concerns about storing large caches of explosives in a politically unstable region with a history of terrorism, Russian authorities eventually agreed to let Olympic planners keep explosive charges that could be fired to cause small avalanches to fall before they develop into larger, more dangerous avalanches.
The same proactive approach to preventing avalanches is being used high in the mountains, where engineers have installed a series of short, metal Gazex pipes. These pipes, open at one end, are designed to blast out an explosive mixture of oxygen and propane when signaled by remote control. The smaller avalanches they cause are expected to prevent the massive buildup of snow that can cause deadly, catastrophic avalanches.
"With the philosophy of controlling them very often, we think we will not have a problem," Jean-Louis Tuaillon, an expert in avalanche mitigation at several European resorts, told The New York Times.
Other approaches to avalanche management at Sochi are decidedly more low-tech, like huge earthen dams — some as high as a three-story building — designed to deflect avalanches away from ski runs and newly constructed Olympic buildings.
While Olympic planners are optimistic that these measures will be effective at mitigating the avalanche risk, there are no guarantees. "Honestly, I don't think the danger is big," Tuaillon told the Times. "But like anywhere in the world, you can have crazy weather. And it is the mountains."