The Raikoke Volcanic Massif, Kuril Island Arc

This study is concerned with the Raikoke volcanic massif, part land, part undersea, situated in the northern Central Kuriles. It consists of Raikoke volcano-island and the Quaternary undersea volcano 3.18. The eruption of June 2019 did considerable damage to the fauna and flora of Raikoke Island, changing its aspect one more time. A lake appeared in its crater. Raikoke volcano-island is composed of moderate potassium rocks of medium alkalinity belonging to the tholeiitic series from basalts to andesites, which are typical arc lavas. This occasion is the first to publish the compositions of six samples taken on the island. The undersea volcano 3.18 at a depth of ~800 m has its base coalescing with Raikoke volcano-island. The near-summit part at depths of 260–230 m has several peaks, while extrusions have been identified in the northeastern and southeastern parts of the base. Volcano 3.18 is composed of andesites and basaltic andesites. The basaltic andesites belong to lavas of the moderately potassium suite in the normal-alkaline series. Our surveys suggest that undersea volcano 3.18 was formed during a geomagnetic reversal. Its edifice was found to contain feeding conduits and peripheral magma chambers.