Maskevarri Ráhppát in Finnmark, northern Norway – is it an earthquake-induced landform complex?

Abstract

Abstract. The Sami word ráhppát means rough bouldery/stony terrain with sharp-relief topography in Finnmark, northern Norway. Ráhppát is a common name in the region of the Younger Dryas landforms, yet the origin of ráhppát has remained obscure. The timing of the Younger Dryas is concomitant with the maximum neotectonic fault instability in Fennoscandia. Hence, earthquake activity may have been one of the contributing factors for the Younger Dryas morphologies. Ráhppát on the Maskevarri fell, classified as a part of Tromsø-Lyngen sub-stage of the Younger Dryas, was studied by means of geomorphology and measurements of electrical-sedimentary anisotropy. Ráhppát was found to be built up of an anastomosing network of stony eskerlike ridges and mounds bordered with arch-shaped and sinusoidal ridges. These bordering ridges exhibit sedimentary (azimuthal soil electrical conductivity) anisotropy parallelto-ridge trends and were interconnected to meltwater gullies suggesting generation through short-lived conduit infills. We did not find electrical-sedimentary evidence to support the concept of englacial thrusting and/or compression, often described for Younger Dryas moraines. Maskevarri Ráhppát is typified by ∼ 500 ponds and small lakes on three different elevations descending in an up-ice direction. These may have generated through late glacial earthquake(s) also contributing to subglacial deformation of Maskevarri Ráhppát.

Geomorphological evidence of paleoseismicity: Surficial and underground structures of Pasmajärvi postglacial fault

“…These small-scale transversal fractures of the glacier were possibly already present before the earthquake, because similar crevasses are caused by glacial quakes and flow of the ice sheet in Greenland and Antarctic ice sheets and Alaskan glaciers (Sauber and Molnia, 2004;Ekström et al, 2006;West et al, 2010). These crevasses create a network of basal fractures/lines, opening new water pathways (West et al, 2010) suitable for subglacial squeezing and/or outbursting of water-saturated debris in a seismic event (Sutinen et al, 2014c). The eastern downflow side of the esker, located on the footwall of the fault, was not affected by the earthquake, possibly because it did not move vertically and vibrate as much as the hanging wall side.…”

Dating of paleolandslides in western Finnish Lapland

“…In Norway, Olesen et al (2013) suggest that the Stuoragurra fault was formed in one seismic event during the final stages of deglaciation at 9300 cal BP or shortly afterwards. Sutinen et al (2014c) suggested that the Maskevarri Ráhppát landform complex in Finnmark, northern Norway was formed by an earthquake soon after the Younger Dryas. In the Norwegian fjords several offshore mass flow sediment deposits have been connected to large-scale magnitude earthquakes during or just before the Younger Dryas at 11 000-11 700 cal BP.…”