Factbox-What caused the deadly avalanche in the Indian Himalayas?

Rescue team members work outside a tunnel after a part of a glacier broke away and caused flood in Tapovan, northern state of Uttarakhand, India, February 8, 2021. REUTERS/Stringer

NEW DELHI (Reuters) - An estimated 200 people are missing and 18 are confirmed killed after an avalanche in India's Himalayan region broke dams, swept away bridges, and left dozens of construction workers trapped in tunnels.

Here are answers to some questions on the disaster: