Authorities in the Indian states of Jammu and Kashmir are concerned that a landslide blocking the Tsarap River (also called the Phuktal River) may lead to a damaging flood downstream.
The landslide, which reportedly occurred on December 31, 2014, sent enough fine-grained debris into the river to create an earthen dam. As of January 20, 2015, that dam was about 600 meters (2,000 feet) long, according to an analysis of satellite imagery collected by the Indian Space Research Organization’s CartoSat-2. The artificial lake that formed behind the dam was nearly 8 kilometers (5 miles) long and covered about 55 hectares (300 acres). Aerials surveys suggest the mound of debris blocking the river was about 60 meters (200 feet) high.
The Operational Land Imager (OLI) on Landsat 8 acquired this image of landslide debris and the barrier lake on January 18, 2015. An image of the same area on December 4, 2014, is shown for comparison. Notice that the river appears wider upstream of the landslide. The river also appears brighter after the landslide because the surface has frozen and a fresh coat of snow coats the ice. Note that the images have been rotated to minimize relief inversion, an optical illusion that can make it difficult to tell the difference between valleys and ridges. The large images available for download have not been rotated.
After surveying the situation on January 18, a team of civilian and military engineers recommended that people who live downstream move to higher ground. They also discouraged authorities from using explosives to clear the blockage as doing so could trigger additional landslides. While the chance of a catastrophic flood is lower with the lake frozen, the risk will increase when temperatures rise in the spring. As a precautionary measure, authorities have closed the Chadar ice trek, a popular route that involves hiking on frozen river ice downstream of the blockage.
“It is hard to know how serious the hazard is given the available information,” noted University of East Anglia geologist David Petley on his blog. “On the face of it, the size of the barrier, the length of the lake, the narrow dam crest, and the possibly weak materials would suggest that it is potentially quite risky.Â But that will depend on the location of people and assets downstream and the nature of the materials that form the dam.Â The first step must be to put a monitoring system on the dam.”
NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Caption by Adam Voiland.
In the wake of the May 12, 2008, earthquake in China, a series of landslides blocked the Jiangjiang River, creating swollen reservoirs that threatened to break through and flood catastrophically. The largest of these lakes, Tangjiashan Lake, threatened roughly 1.3 million people.