Case Studies of Airborne Electromagnetic Survey of Volcanoes

Abstract:

At Mt. Ontake in 1984 and Mt. Kurikoma in 2008, parts of the volcanoes collapsed and large-scale sediment disasters occurred. These events were unrelated to volcanic eruption. We conducted case studies using airborne electromagnetic surveys to investigate the slopes likely to cause landslides on such volcanoes. The surveys were conducted by using a helicopter carrying survey instruments; this method of non-contact investigation acquires specific electrical resistance data by electromagnetic induction. Airborne electromagnetic surveys were conducted of 15 active volcanoes where volcanic events could have serious social implications. These case studies extracted data showing only roughly the areas that were at risk of collapse, but this was the first time that such data on slopes likely to cause landslides and on estimated collapse depths were obtained. It remains necessary to find a method of extracting precise data on the slopes likely to induce landslides on each volcano.

First, we collected the results of the volcano surveys and categorized the properties of the collapsed slopes as cap rock type, extended collapse type, or landslide type on the basis of the topography, geological information, and specific electrical resistivity structure. Second, we investigated whether the properties of each volcano were the same as these typified ones. We also defined a collapse range based mainly on the topography and geological properties and also on the collapse depth, which was based on the specific electrical resistivity structure. We revealed that we could use the defined collapse range and depth to estimate the sediment volume of the slopes that were likely to induce landslides.

Several cases, including Mt. Hokkaido Komagatake, Mt. Azuma, Mt. Asama, and Mt. Ontake, will be introduced in this presentation.