The year 1970 was a busy one on the mountain. Several large expeditions were stationed on the south side, including a Japanese ski expedition starring Yuichiro Miura. This meant upwards of 150 people would have to pass through the Khumbu Icefall, the ever-shifting river of ice that has become one of the most dreaded and lethal features on the route. On April 5, a large avalanche swept into the Icefall, hitting sherpas from the ski expedition. Six were lost. It was the worst tragedy to befall that sherpa community since the 1922 British expedition, and it underscored just how dangerous the work they were doing really was.