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[MTT37-02] Heavy rains inflate the Fuji Volcano: Hydro-geodetic application of GNSS
Keywords:Fuji Volcano, GNSS, hydrogeodesy, rain, uplift, groundwater
Active volcanoes often deform by magmatic activities at depth. Here we report that they may inflate also by hydrological activities induced by heavy rains. Fuji Volcano (Mt. Fuji), central Japan, is the highest mountain in Japan, and its last Plinian eruption (Hoei eruption)occurred in 1707, and ~10 cm of ash fell in Tokyo. Considering its serious impact on society, Mt. Fuji has been intensely monitored with various sensors including permanent stations of global navigation satellite system (GNSS) receivers. Mt. Fuji is also known as a water mountain, surrounded with numerous crystal-clear water springs. Highly porous clinkers between massive lava flow layers of the Younger Fuji volcano serve as groundwater aquifers. They rapidly absorb ~1/2 of the rainwater that fell on the slope. The water rapidly flows down the slope through these aquifers, and springs out at the foothill and feeds the five lakes known as Fuji-Goko. We study how such a hydrological system of Mt. Fuji deforms the volcano from space geodetic approaches.
GNSS stations deployed within ~30 km from the Fuji summit are found to be uplifted by a few centimeters on days of heavy rains associated with typhoons and stationary weather fronts. Such uplifts are possibly caused by instantaneous increase of water pressure withinthe shallow aquifers. They are synchronized with the increase of the Fuji-Goko lake levels and changes in tiltmeters deployed on the mountain slope. Such hydrological inflations of the whole volcano last for a day or two. They occur only on the area covered by older lava flows of the Younger Fuji Volcano and become ambiguous on thick debris layers. Crustal uplifts gradually decay beyond ~40 km from the summit. In regions with sufficient distance from the volcano, the crust behaves normally, i.e., large-area subsidence by rainwater loadingproportional to daily rains (0.1 km^3 volumetric subsidence per 1 Gt total rain) as revealed by Heki & Arief (2022 EPSL).
GNSS stations deployed within ~30 km from the Fuji summit are found to be uplifted by a few centimeters on days of heavy rains associated with typhoons and stationary weather fronts. Such uplifts are possibly caused by instantaneous increase of water pressure withinthe shallow aquifers. They are synchronized with the increase of the Fuji-Goko lake levels and changes in tiltmeters deployed on the mountain slope. Such hydrological inflations of the whole volcano last for a day or two. They occur only on the area covered by older lava flows of the Younger Fuji Volcano and become ambiguous on thick debris layers. Crustal uplifts gradually decay beyond ~40 km from the summit. In regions with sufficient distance from the volcano, the crust behaves normally, i.e., large-area subsidence by rainwater loadingproportional to daily rains (0.1 km^3 volumetric subsidence per 1 Gt total rain) as revealed by Heki & Arief (2022 EPSL).