Late Pleistocene Catastrophic Landslide from the Balaganchik Ridge: Evidence from the Mitoga 2 Reference Section (Western Kamchatka)

A new reference section of the Okhotsk seaside of Kamchatka in the Mitoga 2 River area is studied and dated for the first time ( 14 C and 230 Th/U). Sedimentary deposits were correlated with the previously known sections in the Khomutina‒Mitoga interfluve. It has been established that the sequence of “gray silts and clays” represents deposits of a large lake-type estuary, which began to swamp about 90–80 ka BP, and all sediments overlapping the silts began to form no earlier than 90 ka BP (second half of MIS 5). Deposits of a catastrophic collapse (clastic mass transport over about 100 km, area ≥1500 km 2 , volume ≥15 km 3 ), which descended from the Balaganchik Ridge about 90‒80 ka BP, were identified. Two main facies were established: dispersed basal layer (“moraine-type loam” sequence) and landslide proper sediments (conglomerates). Valleys of the Bystraya and Plotnikova rivers were blocked by a collapse, resulting in the formation of a large dammed lake. The catastrophic drainage of the lake could occur about 37 ka BP. Deposits related to the dam breakthrough are recorded between the Mitoga 2 River and Zuikovo Settlement on the Okhotsk coast.