In a satellite image from 9th August 2017 I saw what appears to be a large grey patch (trending NW-SE) in the sea to the east of Zavodovski Island and to the north-northeast of Visokoi Island. This suspiciously looks like a pumice raft but I'm not 100% sure. If it is, then this means that an undersea eruption must've taken place most likely originating from Protector Shoal Volcano, an active undersea volcano located northwest of Zavodovski Island.
UPDATE 12/8/17: After seeking expert opinions, I've declared this inconclusive.
Possible Pumice raft on 9th August 2017? SOURCE: Terra/MODIS/NASA.