Magnitude and frequency of debris and slush flows in the Khibiny mountain valleys, Kola Peninsula, NW Russia

摘要

Available results for five studied valleys of the KhibinyMountains, Kola Peninsula, suggest that slush flows and, possibly for somevalleys, typical debris flows with lower frequency, are a leading mechanismfor downstream sediment delivery and valley floor topographical formation.Typical fluvial topography in slush flow-affected basins is extremelysuppressed or nonexistent, since under such conditions, stream channels areunable to rework slush flow deposits. The recovery phase of fluvialtopography can serve as an indicator of the magnitude and time passed sincethe last extreme event. A combination of grain size analysis, radionuclidefingerprinting with the 232Th content in the finer-grained sedimentmatrix (size <10 mm) and 14C dating, were applied to revealthe age and common structure of debris and slush flow environments and toinvestigate the main factors in their lithodynamics. Those helped toestimate transportation distances and capacities of the flows and the amountof fluvial reworking of its deposits with time. Application of radiocarbondating to determine absolute ages (about 30 dates) of stabilization periodsfor the colluvial cones, mountain fans and valley bottoms and integrationwith other available chronological data provided a basis for distinguishingseveral stages of decreased activity of debris and slush flows and extremeslope failures through the second half of the Holocene. Field mapping andremote sensing data interpretation revealed spatial distribution patterns ofdebris and slush flows. Geomorphic analysis of large relic landforms invalley bottoms confirms, in general, the case for a significant reduction ofdebris flow magnitude since the last deglaciation and distinct shift toslush flow processes with much lower clastic content. A reliable chronologyof the early events is yet to be obtained representing a challenging problemfor future research.