Debris Flow activity and specificity of Debris Flow Formation in the Geysernaya river valley (KamchatKa)

Abstract

A map of debris flow activity of the Geysernaya river basin, where large-scale debris flow processes associated with the collapse of fragments of the left side of the valley have been observed three times over the past 40 years, was compiled. Three independent debris flow areas of the river basin have been identified and characterized: the upper reaches of the river — the Levaya Geysernaya basin, the middle river course — below the dammed lake formed in 2014, and the lower downstream part — below the dammed lake that existed in 2007–2014. It was found that debris flow processes are typical for most of the Geysernaya river tributaries. Moreover, in the left tributaries debris flows may have aseasonal character, because they are formed in conditions of constant heating and active gas-hydrothermal influence within the thermal fields. The landslide dam formed in 2014 is resistant to erosion, and an independent breakthrough of the dammed lake is unlikely. With further erosion of the 2007 dam and the expansion of the breach in the dam body, collapse of its sides and debris flow in the lower part of the Geysernaya river valley cannot be ruled out. Risks of rockfall, landslide and debris flow processes, the initiation of which is most likely on the left side of the valley, should be considered in planning the development of recreational facilities.