Today, scientists think these people were killed by giant hailstones-bails of ice. Hailstones form when raindrops high in the sky turn into pieces of ice. he ice pieces increase in size until the wind cannot hold them up. This results in hailstones falling to the ground, often at speeds of over 160 kilometers (100 miles) an hour. For the unlucky people at Lake Roopkund, there was nowhere to run. They were all killed by the hailstones.