Glacial landforms and deposits in the Uksichan River valley, central Kamchatka, Russia

In this paper, we provide preliminary data concerned with advance and retreat of large-scale valley glaciers in the late Quaternary age in the lowest part of the Uksichan River Basin, where no remarkable glacier currently exists, even in the uppermost high-altitude area. The Uksichan River, a tributary of the Bystraya River whose drainage basin is distributed in the Sredinny Range, flows from the Uksichan Volcano (1,692 m a.s.l.), approximately 30 km WNW of Esso, the principal town of the Bystrinsky District, central Kamchatka. Gentle slope surfaces, i.e. Surfaces I to VI in descending order, are attached to the valley-side slopes of the broad U-shaped river valley, and the summit level of the low-relief area on the valley bottom is defined as Surface VII. We observed subsurface deposits particularly along a landslide zone, occurring in 1997, where rocks and sediments are better exposed, and in the whole investigated area. From the mode and characteristics of the glacial deposits constituting the respective surfaces, and from micro-landforms in that area, Surfaces II, IV, V, and VI correspond to the advancing stages of the glacier, namely, the Bystraya Stage 2, the Esso Stages 1, 2, and 3, and prior to these stages, a U-shaped valley formed along the Uksichan River in the oldest glacier advancing stage (Bystraya Stage 1). All of these stages certainly date back to the Neoglaciation age (ca. 3 ka) on the basis of tephrochronology, especially the presence of SH₃ (1.3-1.4 ka: Shiveluch Volcano origin) and KS₁ (1.7-1.8 ka: Ksudach Caldera origin). Specifically, the glaciers in these stages extended approximately 30 km or more from the Uksichan Volcano and the surrounding mountains, where the accumulation zones were widespread. We presume that the glacier terminus in the Esso Stages 1 to 3, was situated near Esso. No considerable difference in stratigraphy of the tephra layers, however, can be found even between the surfaces of different levels, whereas it is evident that these surfaces formed in different ages. Thus, other dating methods need to be adopted to permit discussion on the detailed periods of glaciation in the Uksichan River area. Moreover, further studies on the sedimentary structures and the deformation of glacial deposits are necessary in order to clarify the detailed glacial environment in each advance stage.