Japan is one of the world’s leading volcanic countries, hosting 111 active volcanoes (about 7% of the world’s active volcanoes). Volcanoes provide many benefits to human society, including scenic landscapes, hot springs, and fertile soils, while also posing hazards through eruptions and related phenomena. For this reason, continuously monitoring volcanic activity is essential for mitigating disasters and protecting lives and property.
At active volcanoes, magma and hydrothermal fluids migrate underground as volcanic activity evolves, causing deformation of the volcanic edifice. Such deformation can be observed at the Earth’s surface. Therefore, observing ground deformation helps reveal the location and movement of magma and hydrothermal fluids, improves our understanding of ongoing volcanic activity, and contributes to more accurate forecasting of future activity and eruptions.
Volcanic activity occurs over a wide range of time scales. For example, at Campi Flegrei in Italy, uplift of the ground has continued for several decades without culminating in an eruption. At Shinmoedake (Kirishima Volcano), which erupted in 2011 and 2018, edifice inflation persisted for roughly a year prior to the eruptions. Furthermore, many volcanoes exhibit pronounced deformation over much shorter time scales—days or even hours—immediately before an eruption. Post-eruptive deformation also varies: in some cases it ceases, in others contraction continues, and in still others reinflation begins soon after. Accordingly, continuous observations with fine temporal resolution are crucial for understanding volcanic processes.
In addition, surface deformation at most volcanoes is observed over relatively small spatial scales, typically within several kilometers of the crater. In particular, just before an eruption, deformation may occur on scales of several hundred meters to a few kilometers around the vent. Thus, capturing and forecasting volcanic activity requires not only high temporal resolution but also spatially dense observations.
SoftBank’s proprietary GNSS reference network achieves both high temporal resolution and high spatial density. By leveraging this network, we expect to obtain a more detailed characterization of volcanic activity and to improve the accuracy of activity assessment and eruption forecasting.