Relict blockstreams at Insteheia, Valldalen-Tafjorden, southern Norway: Their nature and Schmidt-hammer exposure age

• Published in: Permafrost and Periglacial Processes
• Main Authors: Wilson, P., Matthews, J., Mourne, R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: John Wiley & Sons 2017
• Subjects: Norway; permafrost; Permafrost and Periglacial Processes
• Online Access: http://eprints.uwe.ac.uk/30468/; http://eprints.uwe.ac.uk/30468/1/Blockstream%20pdf.pdf; https://doi.org/10.1002/ppp.1915

Two small blockstreams, the first such landforms to be recorded in the mountains of Scandinavia, are described from Insteheia, a col at 910 m asl on the watershed between Valldalen and Tafjorden (Møre og Romsdal), southern Norway. Both blockstreams display morphological and sedimentological characteristics indicative of boulder accumulations that have moved downslope by means of solifluction most probably under a permafrost climatic regime. These comprise boulder preferred orientation and dip patterns; inverse grading comprising surface boulders overlying successively finer, well-sorted cobble, pebble and finegrained (sand/silt dominated) sediment layers; imbrication, with the packing of small boulders behind larger boulders; and proximity to boulder-strewn hillslopes whose constituent boulders (organised into lobes and terraces) feed downslope into the blockstreams. Schmidt-hammer exposure-ages of 7.24 to 11.17 ka indicate that the blockstreams were last active during the Younger Dryas Stadial – Holocene transition (~9.5-11.2 ka). It is inferred that blockstream development began at ~18 ka, following the Last Glacial Maximum, and lasted for ~8 ka, and that since the blockstreams became inactive fine grained material has been progressively lost as a result of snowmelt runoff. The small areal extent and relatively recent age of the blockstreams contrast with larger-scale forms of considerably greater age in the Southern Hemisphere.