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Research aims to predict landslides through smell sensors

An area hit by landslides is seen in this Aug. 20, 2014 file photo taken in Asakita Ward in the city of Hiroshima, Hiroshima Prefecture. (Mainichi/Ryoichi Mochizuki)

Researchers and a resident from part of the western Japan prefecture of Hiroshima that was hit by deadly landslides in 2014 have teamed up to develop sensors that can detect the earthy smell said to emanate before a landslide occurs.

It is hoped that this unusual type of sensor could alert people to the threat of a landslide at an early stage and help them evacuate before disaster strikes. The researchers, including Masahiro Nishi, a professor at Hiroshima City University, hope to complete the system this fiscal year.

"With a lot of landslides occurring, we want to encourage people to evacuate and lessen the damage," Nishi said.

According to Toshitaka Kamai, a professor in applied geology in the Disaster Prevention Research Institute at Kyoto University, foreboding signs are often observed before a landslide -- such as a stinky smell emerging or river water becoming muddy. Although the mechanism behind the smell has not yet been unraveled, Kamai says, "It's thought one factor is that the land formation changes when earth and sand collapse, opening cracks in the ground."

The Miiri district of Hiroshima's Asakita Ward saw two landslide fatalities. Nobuhiro Atarashiki, the 68-year-old head of a federation of voluntary disaster prevention associations in the district, heard from several residents that a smell like stinky mud emerged before the landslide occurred. He had been in contact with Nishi, who had been involved in disaster prevention, releasing images of water levels to residents, and suggested that they might be able to warn residents of the danger from the smells emitted before a landslide. They began joint research last year.

Nishi says that the research makes use of off-the-rack sensors designed to detect gas leaks. They are shaped like small microphones with a diameter of 1.5 centimeters, and react to methane gas and other substances behind smells. When the sensor detects a certain smell, it sends out a signal via Bluetooth wireless technology. The researchers aim to send this through a relay device to residents' smartphones and TVs to inform them of dangerous areas. This would enable residents to acquire information even when the internet and phone lines are down.

Researchers are collecting smell data, which they will use to set voltage levels on the sensors in areas at risk of landslides. In early September, Nishi and students from his laboratory conducted an experiment creating an artificial landslide on the slope of a hill in the Miiri district. To do so they poured over the area an amount of water equivalent to about 100 millimeters of rain falling over a one-hour period.

Says Nishi, "The smell is influenced by the direction of the wind, so we need to conduct experiments in various areas and find the level of smells that represent danger."

Atarashiki, meanwhile, commented, "If people have multiple sources on which to base their judgments, then they will be able to evacuate quickly without relying on information from administrative bodies alone."

(Japanese original by Misa Koyama, Hiroshima Bureau)

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