ИСТИНА

Slushflows represent a specific type of gravitational flow of water-saturated mixture of snow with limited amount of clastic sediment. Recent large events, some with fatal consequences, reported for Scandinavia, have increased the scientific community and public awareness and social demands for reliable risk assessment and protective measures. Here we report an attempt to reconstruct slushflow activity, evaluate its contribution into sediment budgets and impact on geomorphic structure and fluvial processes in the Khibiny Mountains valleys by means of detailed description of associated landforms and correlated deposits analyses (grainsize, radionuclide fingerprinting, 14C dating). Slushflows of the Khibiny Mountains were thoroughly investigated over the last 50 years; however, focus laid primarily on monitoring consequences of observed events and developing recommendations for mining infrastructure protection. Hence, we believe that our study can add some new perspective to that unique existing dataset. Available results for the five studied valleys suggest slushflows and even debris flows with lower frequency as a leading mechanism of downstream sediment delivery and valley floor transformation. Recurrence interval of medium-magnitude slushflows does not exceed 10-30 years, though fluvial topography is suppressed or nonexistent as streams are unable to rework slushflow deposits. Frequency of extreme events is much lower. For example, large non-vegetated debris fan of the Alyavumjok valley is at least 90 years old. Interval between extreme events in the Mannepahkuaj valley causing debris fans within the piedmont forested zone is about 500 years (according to 14C dating of humic layers separating slushflow deposit bodies). Nevertheless, largest-scale floor features and piedmont fans for the majority of small valleys can most likely be related to much more intense events associated with deglaciation stages and, specifically, bursts of moraine-dammed lakes. Reliable chronology of those stages is yet to be obtained and represents the most challenging problem for future research in the area.