The Geysernaya River Alluvium (Kamchatka): Composition and Features of Formation

• Published in: Doklady earth sciences 2023-07, Vol.513 (Suppl 1), p.S1-S11
• Main Authors: Lebedeva, E. V., Zakharov, A. L., Mikhalev, D. V.
• Format: Article
• Language: English
• Subjects: Alluvial deposits; Alluvium; Analysis; Boulders; Calderas; Clay; Composition; Debris flow; Deposition; Disintegration; Earth and Environmental Science; Earth Sciences; Fluvial sedimentation; Fluvial sediments; Fragments; Geomorphology; Gravel; Hydrothermal activity; Inflow; Minerals; Mudflows; Pebbles; Reservoirs; River beds; River erosion; River valleys; Riverbeds; Rivers; Rock; Rocks; Roundness; Sand; Sediment; Sediments; Sediments (Geology); Slopes; Smectite; Smectites; Terraces; Water inflow; Weathering; Zeolites
• ISSN: 1028-334X; 1531-8354
• DOI: 10.1134/S1028334X23602432

A comprehensive analysis of the composition of the alluvium of the river with active gas–hydrothermal occurrences has been carried out for the first time. Common features in the lower and middle reaches of the Geysernaya River include poor roundness of boulders and pebbles (grades 1–2), poor grading of alluvium fine-clastic components, abundant rock fragments, and mineral intergrowths even in the fine-sand fraction. All this information is indicative of weak sediment disintegration and a high proportion of slope material in sediments, including that redeposited by mudflows. High contents of smectite–zeolite and other newly formed (secondary) mineral aggregates (up to 70% of the light fraction of 0.1–0.25 mm in size) and altered rock fragments (up to 70–80% in the pebble fraction of alluvium) make it possible to suggest a great effect of gas–hydrothermal activity on the processing of river-eroded rocks, as well as the secondary weathering of the alluvium within the thermal fields. The riverbed deposition is fragmentary and predominant in the areas of (1) the active slope material inflow (temporary dams), (2) flattening of the longitudinal profile in dammed reservoirs, and (3) mudflow material removal. Two dammed reservoirs formed over the past 15 years, as well as fine-sand layers in the low-terrace sediments are indicative of the fact that the Geysernaya River valley is characterized by the periodic formation of such short-lived basins. The deposition conditions of the fine-sand alluvium are different in sections of a single-branch channel and within dammed reservoirs and affect the ratio of the principal minerals of the heavy fraction. Abundant well-rounded gravel and coarse sand and their weathered appearance make it possible to assume that, along with the processing of large volumes of incoming slope and mudflow material, the Geysernaya River continues to cut in and to erode ancient fluvial sediments probably of the pre-caldera stage.