Slope processes in cold environments of Northern Finland

Abstract

Local slope processes were studied in view of their geomorphologic features, action environments, lichenometrical chronology and capacity to displace debris. The research areas were high relief massifs of four different litho­logies, located in the periglacial zone of sporadic‑discontinuous permafrost today. The local lithology has determined the mode of rock breakup. Autoch­tonous block fields leave not been formed since deglaciation, with a few exceptions; the comminutive rates since have been low. Rockslide has been important where oblique bedding planes provide environments for continuous sliding. Rockfalls have been restricted to proglacial channels and cliffs. Mean recession rates for Holocene vary between 0.04‑0.94 mm a^‑l; recent values between 0.07‑0.18 mm a ^-1. Most falls have coincided with cold spells in spring. Avalanching has played an important role in sculpturing channel‑ and rockwalls. Nivation has been restricted to pro­glacial drainage channels; the mean undercutting rates of scarps range between 0‑0.27 mm a ^{‑ 1} for Holocene. Recent surficial block creep rates vary between 0.6‑2.4 cm a^‑1; solifluction rates between 0.5‑1.3 cm a^‑1. Creep is of importance in areas with long coarse‑debrised slopes and it requires freeze‑thaw alternations; solifluction beside these also intensive snow melt. Slope wash is the predominant sculpturing process of most areas today. The chemical denudation averages to a relief lowering of 28‑62 mm in Holocene. Sheet erosion acts on N‑E facing slopes, mainly below snow drifts; locally causing 17‑1.5 mm a^‑1 soil subsidence. Landslides and defla­tion have played insignificant roles on the studied slopes. Most episodic phenomena coincide with cold spells or subsequent phases in Holocene; whereas patterned ground development, solifluction, creep and rockfall were intensified after the Holocene climatic optimum. Most recent processes are associated with snow drifts and contribute to develop a valley asymmetry. The physical relief lowering ranges between 2‑21 mm for Holocene, whereas the existent asymmetry of the valleys is inherited from epochs.