Until 2017, Bolshaya Udina in the Klyuchevskaya volcano group in Kamchatka was considered extinct as there is no record of past eruptions. However, in 2017 seismic activity prompted researchers to investigate the volcano, a difficult task because of its remoteness. They installed four seismic stations and monitored activity in May-June 2018. The seismic events were located at ~5 km depth. The news media (and Russian scientists) are likening the possibilties to Vesuvius in 79 A.D. or Bezymianny in 1956. Bezymianny, in turn, was a near duplicate of Mount St. Helens May 18 eruption in 1980. All are in the dangerous class of "andesitic volcanoes" which tend to have very explosive eruptions. As far as I can tell, there are no publications on the volcano other than the mention that it's a volcanic "massif" consisting of two stratovolcanoes SE of Tolbachik volcano. It is 2923 m high (~9650 feet) and has a lava dome on its SW flank. The cluster of seismic events connects Bolshaya Udina with the Tolud zone to the southwest--a zone where seismicity in the middle and lower crust that is believed to have fed the Tolbachik fissure eruptions. The magma has migrated from this zone toward Udina. The low shear velocities measured suggest that the zone is rich in melt and volatiles. For more information on Udina, see Koulakov et al., JVGR 379, 45-59, 2019.
There was an interesting paper** published in 2017 about three close neighbor volcanoes: Klyuchevskoy, Bezymianny, and Tolbachik (see map). They are among the most active volcanoes in the world and yet have very different eruption styles. Klyuchevskoy has basaltic lavas supplied from a reservoir at about 25-30 km depth through a vertical conduit. Bezymianny's magma comes through a dispersed system of reservoirs in the crust. In these reservoirs, the andesitic component separates from the more mafic component and rises into the upper crust where it can erupt explosively. Tolbachik has low-viscosity basalts that ascend through fractures associated with intersections of regional faults.
**Koulakov, I., et al., JGR-Solid Earth, 122(5), pp. 3852-3874, 2017.
