Sunday 21 July 2019

Rockfall kills eight-month-old girl in Himachal Pradesh.

An eight-month-old girl has died and seven other people, including two other children, have been injured after a group of tourists was hit by a rockfall in Kangra District in Himachal Pradesh, India, on Saturday 20 July 2019. All of those involved are believed to have come from two families from Haroli in Una District, also Himachal Pradesh, who were walking on a trail between Bhagsu Nag Temple and the Bhagsu Nag Waterfall at the time of the incident. The landslide is the latest in a series of events connected to heavy rains in the area, brought on by the onset of the Indian Summer Monsoon. Mountainous areas of Himachal Pradesh (which is most of the state) are notoriously prone to landslips and rockfalls, particularly during the monsoon season, which lasts from July to September, when very high rainfall levels can trigger many such events. Landslides are a common problem after severe weather, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.

The scene of the 20 July 2019 Bhagsu Nag rockfall. Kamaljeet/The Tribune.

Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate. This situation is particularly intense in South Asia, due to the presence of the Himalayas. High mountain ranges tend to force winds hitting them upwards, which amplifies the South Asian Summer Monsoon, with higher winds leading to more upward air movement, thus drawing in further air from the sea. 

 Diagrammatic representation of wind and rainfall patterns in a tropical monsoon climate. Geosciences/University of Arizona.

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