The Mount Everest south base camp in Nepal is seen a day after a huge earthquake-caused avalanche killed at least 17 people, in this photo courtesy of 6summitschallenge.com taken on April 26, 2015 and released on April 27, 2015. Rescue teams, helped by clear weather, used helicopters to airlift scores of people stranded at higher altitudes, two at a time. REUTERS/6summitschallenge.com ATTENTION EDITORS – NO SALES.NO ARCHIVES. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. MANDATORY CREDIT.NO COMMERCIAL USE.