In the past few days there have been a number of deaths on ski slopes in the Alps and, in recent months, hikers in Greece, climbers in Italy’s Dolomite mountains, and guides in the Himalayas have all lost their lives.The peak season for these huge and potentially lethal mass movements of snow is now underway in the northern hemisphere. To understand the dangers, and what it’s like to experience an avalanche, we hear from three survivors. For mountaineer Cory Richards in South Africa, the impact of an avalanche while climbing the world's 13th tallest mountain in Pakistan left him and his two climbing partners thinking they were all about to die.