A wave-powered glider allows continuous monitoring of volcanic activity around Japanese islands

Wave-powered glider monitors volcanic activity in Japanese waters

Image credit: Kobe University

An autonomous wave-powered glider has been developed by Japanese researchers to monitor volcanic activity in the sea around the Nishinoshima island, which has been worrying researchers due to ongoing eruptions since 2013.

The glider, developed by researchers from Kobe University Graduate School of Science, the University of Tokyo Earthquake Research Institute and the Japan Agency for Marine-Earth Science and Technology, is fitted with multiple cameras for visual observation of the volcano, a GPS wave gauge that can detect tsunami caused by volcanic collapse, and a gauge that checks for earthquakes and air vibrations by measuring sonic waves in the air and water.

During the latest round of testing, the system was able to accurately transmit data in real time to a server on the Japanese mainland some 1000km away using a satellite link.

The team plans to use such gliders on a larger scale to continuously monitor tectonic and volcanic activity around Japan's remote islands to improve disaster prediction and preparedness.

Thanks to its ability to obtain power directly from the waves, the glider can operate continuously for long periods of time.

The device consists of a floating platform connected via a 5.8m cable to an underwater glider that harnesses the power of the waves.

The floating platform carries most of the scientific sensors including a device to detect earthquakes and air vibrations, a GPS tsunami meter, and two sets of transmission devices including a satellite communication terminal to transmit the observation data via satellite.

A hydrophone is attached to the underwater glider for monitoring sonic waves. Four time-lapse cameras capture a continuous 360-degree image of the glider’s surroundings.

During the tests, the system autonomously sailed around Nishinoshima in a circular path with a 5km radius and returned to the base after a day.

Nishinoshima, part of the Ogasawara island chain, has been experiencing active volcanic eruptions since November 2013. The new island formed by the lava flow has continued to grow, expanding to 2km in diameter as of August 2015. After late November 2015 the eruptions that produce ash deposits and lava flows stopped, and further eruptions that will affect large areas of the island are unlikely to occur.

These volcanic activities on Nishinoshima are a valuable opportunity to understand the processes behind submarine volcanic eruptions and the growth of new volcanic islands. Until recently, observation of the volcano was mainly carried out by artificial satellites and a monthly aircraft visit by the Japan Coast Guard.

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