Taishi Yamada

Magnitude–frequency distribution of volcanic explosion earthquakes

Magnitude–frequency distributions of volcanic explosion earthquakes that are associated with occurrences of vulcanian and strombolian eruptions, or gas burst activity, are examined at six active volcanoes. The magnitude–frequency distribution at Suwanosejima volcano, Japan, shows a power-law distribution, which implies self-similarity in the system, as is often observed in statistical characteristics of tectonic and volcanic earthquakes. On the other hand, the magnitude–frequency distributions at five other volcanoes, Sakurajima and Tokachi-dake in Japan, Semeru and Lokon in Indonesia, and Stromboli in Italy, are well explained by exponential distributions. The statistical features are considered to reflect source size, as characterized by a volcanic conduit or chamber. Earthquake generation processes associated with vulcanian, strombolian and gas burst events are different from those of eruptions ejecting large amounts of pyroclasts, since the magnitude–frequency distribution of the volcanic explosivity index is generally explained by the power law.

Volcanic eruption volume flux estimations from very long period infrasound signals

We examine very long period infrasonic signals accompanying volcanic eruptions near active vents at Lokon-Empung volcano in Indonesia, Aso, Kuchinoerabujima, and Kirishima volcanoes in Japan. The excitation of the very long period pulse is associated with an explosion, the emerging of an eruption column, and a pyroclastic density current. We model the excitation of the infrasound pulse, assuming a monopole source, to quantify the volume flux and cumulative volume of erupting material. The infrasound-derived volume flux and cumulative volume can be less than half of the video-derived results. A largely positive correlation can be seen between the infrasound-derived volume flux and the maximum eruption column height. Therefore, our result suggests that the analysis of very long period volcanic infrasound pulses can be helpful in estimating the maximum eruption column height.

Correction to: Magnitude–frequency distribution of volcanic explosion earthquakes

Magnitude–frequency distributions of volcanic explosion earthquakes that are associated with occurrences of vulcanian and strombolian eruptions, or gas burst activity, are examined at six active volcanoes. The magnitude–frequency distribution at Suwanosejima volcano, Japan, shows a power-law distribution

Relationship between infrasound-derived and buoyancy-derived eruption plume volume estimates

Volume estimations for discrete plumes accompanying short-lived eruptions are potentially possible using infrasound signals. Plumes emitted during short-lived (discrete) eruptions have been modeled as discrete thermals or rooted thermals. Based on the one-dimensional model for the rise of a discrete thermal, the initial buoyancy, F0, of a spherical thermal can theoretically be estimated from the maximum plume height and a vertical profile of ambient air density. We here examine the relationship between infrasound-derived volume, Vinf, and the buoyancy-derived volume, Vb, as derived from F0, which depends on gravity acceleration, and the difference in density between the thermal and surrounding air, to understand how Vinf relates to the dynamics of the eruption plume. We analyze infrasound data accompanying Vulcanian and phreatic eruptions at Aso, Shinmoedake, and Lokon-Empung volcanoes to estimate Vinf, and consider Vinf from other volcanoes. We obtain a representative ratio of Vb/Vinf of 16 by examining 53 events. Because the analyzed infrasound signals share a prominent pressure pulse at the onset, we regard Vinf as the volume of the plume at initiation, i.e., as a jet. Instead, we consider Vb as the thermal volume when it has entrained a sufficient amount of the surrounding air and obtains F0. Comparison of the bulk density of the jet and the discrete thermal yields a rate of volume change between both regimes by a factor of 1.8–32, which is consistent with the ratio of Vb/Vinf. Our result provides an effective index to constrain erupted plume volume using infrasound data with real-time monitoring systems.