Abstract
Abstract. Available results for five studied valleys of the Khibiny Mountains, Kola Peninsula, suggest that slush flows and, possibly for some valleys, typical debris flows with lower frequency, are a leading mechanism for downstream sediment delivery and valley floor topographical formation. Typical fluvial topography in slush flow-affected basins is extremely suppressed or nonexistent, since under such conditions, stream channels are unable to rework slush flow deposits. The recovery phase of fluvial topography can serve as an indicator of the magnitude and time passed since the last extreme event. A combination of grain size analysis, radionuclide fingerprinting with the 232Th content in the finer-grained sediment matrix (size <10 mm) and 14C dating, were applied to reveal the age and common structure of debris and slush flow environments and to investigate the main factors in their lithodynamics. Those helped to estimate transportation distances and capacities of the flows and the amount of fluvial reworking of its deposits with time. Application of radiocarbon dating to determine absolute ages (about 30 dates) of stabilization periods for the colluvial cones, mountain fans and valley bottoms and integration with other available chronological data provided a basis for distinguishing several stages of decreased activity of debris and slush flows and extreme slope failures through the second half of the Holocene. Field mapping and remote sensing data interpretation revealed spatial distribution patterns of debris and slush flows. Geomorphic analysis of large relic landforms in valley bottoms confirms, in general, the case for a significant reduction of debris flow magnitude since the last deglaciation and distinct shift to slush flow processes with much lower clastic content. A reliable chronology of the early events is yet to be obtained representing a challenging problem for future research.
Highlights
The largest mountain massif of the Kola Peninsula – Khibiny – is comprised of Devonian alkaline intrusions (Pozhilenko et al, 2002)
Along the middle reaches of 2nd and 3rd order streams, they are traced as sequences of inclined terraces. They appear as a series of humic or peat layers buried between coarse deposits in slush flow fans
Available results for the Khibiny Mountains suggest slush flows and typical debris flows with lower frequency are both leading mechanisms and underestimated agents of downstream sediment delivery and valley floor topographical formation during the Holocene
Summary
The largest mountain massif of the Kola Peninsula – Khibiny – is comprised of Devonian alkaline intrusions (Pozhilenko et al, 2002). Compact plateau-shaped mountains (up to 1201 m a.s.l.), with relatively steep slopes, are dissected by numerous deep (100–400 m) erosional valleys, glacial troughs and cirques, and tectonic lineaments. Especially in apatite and nepheline ores and rare earth elements (Fig. 1), Khibiny have been intensely explored since the 1920s. The area has become a focus of a rapidly growing recreational industry. At the same time as being an arena of widespread natural hazards, its industrial and civil infrastructure (ski resorts, newly established National park, quarries, mines, plants, roads, etc.) is strongly affected by snow avalanches, rockfalls, screes, and debris flows (Belyaev et al, 2015). The most frequently observed types of the latter are snowmelt period slush flows and rainfallinduced medium magnitude debris flows (Perov et al, 2017)
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