12:00 PM - 12:15 PM
[SVC34-06] Issues in volcano monitoring for future eruptions in Hokkaido
Keywords:volcano monitoring, assessment of volcanic activity
Five major active volcanoes (Hokkaido-Komagatake, Usuzan, Tarumaesan, Tokachidake, Meakandake) have repeated volcanic eruptions in Hokkaido. A total of 10 magmatic eruptions occurred in the 20th century, causing severe disasters due to volcanic mudflows, ground deformation, and pyroclastic falls, and many small phreatic eruptions have also been reported. Since the end of the 2000 eruption of Usuzan, however, there was no magmatic eruption for more than 20 years, which is an unprecedented long calm period after the 20th century. The eruption history of the major volcanoes strongly indicates that the magmatic eruption will resume sooner or later. Explosive phreatic eruption during the calm period is also a major threat to volcano disaster mitigation, as reaffirmed by the eruptions of Ontakesan in 2014 and Motoshiranesan in 2018. At Hokkaido-Komagatake and Tokachidake, phreatic eruptions have often preceded magmatic eruptions in the past, and at some volcanoes, such as Kuttara, crater areas of the past phreatic eruptions are very close to the residential area. It is significant to summarize the current situation and issues of volcano monitoring for each volcano in terms of assessment of volcanic activity, research monitoring during eruptive activity, and rapid response for disaster mitigation. In this summary, we focus on a few important volcanoes.
Hokkaido-Komagatake
In the case of a magmatic eruption, VEI-2 (1942 eruption) to VEI-4 (1929 eruption) class activity is expected. There is little knowledge about precursory phenomena, but phreatic eruptions have occurred for several years before two magmatic eruptions in the 20th century. The monitoring networks of the Japan Meteorological Agency and Hokkaido University are deployed around the summit area, so we can expect to detect precursors to phreatic eruptions if they exist. The past magmatic eruptions of Hokkaido-Komagatake were characterized by large amounts of pumice ejection and rapid evolution of eruptive activity. Pyroclastic flows due to eruption column collapse have often occurred when the eruption was intensified. It is important to keep in mind that a large eruption may occur and to consider the observation and analysis that can be used for the immediate estimation of the discharge rate of magma.
Usuzan
The sequence of eruptive activities can be tracked by the dense monitoring network around the volcano. Frank eruption close to a residential area can be expected as in the 2000 eruption, so it is important to establish a monitoring system that can immediately detect the extent of impact due to the eruption.
Tokachidake
Multi-parameter monitoring near the active crater has enabled us to observe various phenomena excited at the shallow part of the mountain, such as ground deformation, very-long-period earthquakes, and thermal demagnetization. Recent surface phenomena are similar to the long-term precursors of past magmatic eruptions, and therefore, evaluation of the imminence of future eruptions is an important issue. However, since the long-term magma eruption rate is low and the monitoring station is mainly distributed on the northwestern side of the volcano, it is very difficult to detect the magma accumulation from geodetic observations. Phreatic eruption and sector collapse are also major concerns for volcanic disaster mitigation because Tokachidake has a well-developed hydrothermal system. VUI is one of the trial approaches to evaluate the imminence of phreatic eruptions. The western slope of Maetokachi peak may be unstable due to the long-term inflation in this area and alteration associated with the expansion of the geothermal area. We should consider additional observation and disaster mitigation plans assuming the sector collapse around Maetokachi peak.
Hokkaido-Komagatake
In the case of a magmatic eruption, VEI-2 (1942 eruption) to VEI-4 (1929 eruption) class activity is expected. There is little knowledge about precursory phenomena, but phreatic eruptions have occurred for several years before two magmatic eruptions in the 20th century. The monitoring networks of the Japan Meteorological Agency and Hokkaido University are deployed around the summit area, so we can expect to detect precursors to phreatic eruptions if they exist. The past magmatic eruptions of Hokkaido-Komagatake were characterized by large amounts of pumice ejection and rapid evolution of eruptive activity. Pyroclastic flows due to eruption column collapse have often occurred when the eruption was intensified. It is important to keep in mind that a large eruption may occur and to consider the observation and analysis that can be used for the immediate estimation of the discharge rate of magma.
Usuzan
The sequence of eruptive activities can be tracked by the dense monitoring network around the volcano. Frank eruption close to a residential area can be expected as in the 2000 eruption, so it is important to establish a monitoring system that can immediately detect the extent of impact due to the eruption.
Tokachidake
Multi-parameter monitoring near the active crater has enabled us to observe various phenomena excited at the shallow part of the mountain, such as ground deformation, very-long-period earthquakes, and thermal demagnetization. Recent surface phenomena are similar to the long-term precursors of past magmatic eruptions, and therefore, evaluation of the imminence of future eruptions is an important issue. However, since the long-term magma eruption rate is low and the monitoring station is mainly distributed on the northwestern side of the volcano, it is very difficult to detect the magma accumulation from geodetic observations. Phreatic eruption and sector collapse are also major concerns for volcanic disaster mitigation because Tokachidake has a well-developed hydrothermal system. VUI is one of the trial approaches to evaluate the imminence of phreatic eruptions. The western slope of Maetokachi peak may be unstable due to the long-term inflation in this area and alteration associated with the expansion of the geothermal area. We should consider additional observation and disaster mitigation plans assuming the sector collapse around Maetokachi peak.