Wednesday, 31 July 2019

Landslide kills father and son in Maharashtra State, India.

Two people have died after a landslide destroyed their home in Thane in northern Maharashtra State, India, on Tuesday 30 July 2019. Birendra Jaswal, 40 and his son Sunny Jaswar, 10, were sleeping in the building when part of a hillslope collapsed onto it. They were rushed to the Chatrapati Shivaji Hospital in Kalwa for treatment, but both died of their injuries. Jaswar’s wife Neelam, 35, was also injured and is being treated in the hospital, where her condition is described as 'stable'/ Local authorities have evacuated another nineteen families from fifteen nearby homes, which they describe as having been built illegally by unscrupulous landlords on the flanks of Parsik Hill, which is notoriously unstable following years of illegal quarrying and deforestation. The evacuated families are being housed temporarily at a nearby school while the properties are demolished. What long term plans the authorities have for rehousing them are unclear.

The aftermath of a landslide on the side of Parsik Hill in Thane that killed two people. Hindustan Times.

The area where the incident occurred is known to suffer a high risk of landslides, particularly during the  monsoon season when high rainfall frequently triggers such events. Landslides are a common problem after severe weather events, 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. To this end the slopes above the expressway had been re-enforced against such events. However local press sources are reporting that these defences are largely iron in construction, and in places are showing signs of severe corrosion.

Maharashtra State has a monsoon climate, with the rains typically arriving around the start of June and peaking in July. The area where the 19 July 2015 landslip occurred typically receives over 500 mm of rain in June and over 1300 mm in July, and the area suffers frequent landslip and flooding events. This situation is made worse by widespread deforestation and quarrying for construction materials (much of it illegal) which tends to destabilise hill slopes.

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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