On March 24, 1996, because of extraordinary heavy storms, a big snowball of 10m long×20m wide×3m thick in Ra'og mountain of Bome District rolled down from the mountain top of 300 meters high and buried more than 20 trucks that were passing the highway, more than 500 workers from Sichuan, all the local people and soldiers were also buried by it. Among them, 56 workers and Tibetans on the five trucks were killed on the spot; the rest 460 people could only stretch out their heads; some others were blocked by ice blocks and could not move at all.