Introduction

1. Surface displacements and surface age estimates for creeping slope landforms in Northern Iceland using digital photogrammetry B. Wangensteen¹, Á. Guðmundsson2 , T. Eiken¹, A. Kääb3, H. Farbrot1 and B. Etzelmüller11.Department of Geo Sciences, University of Oslo, P.O.Box 1047 Blindern, 0316 Oslo, Norway2. Jarðfræðistofán Geological Services, Raudðagerði 31, 108 Reykjavik, Iceland3. Department of Geography, University of Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich, SwitzerlandE-mail:bjorn.wangensteen@geo.uio.no Introduction In this study, two areas of different active coarse debris slope processes are investigated in Northern Iceland. The objective of the study was to assess slope dynamics in high-mountain terrain on Iceland, and its possible implication to mountain permafrost distribution and Holocene landscape development. Surface displacements of glacier derived rock glaciers and a debris-covered glacier in the Hólar area and a moving debris accumulation at Almenningsnöfclose to Siglufjörður are measured. The displacement fields are obtained by cross-correlation matching of multi-temporal orthophotos (cf. Kääb & Vollmer, 2000). Orthophotos are generated from various series of air photos from 1964 to 1994. Figure 4: a) Annual displacement from 1985 to 1994 for the rock glacier complex at Hólarb) age estimates based on the same velocity field Moving debris accumulation at Almenningsnöf The moving debris accumulation is located at the road along the coast to Siglufjörður at the northern tip of the Tröllaskagi peninsula (66°10'N, 19°W). Geodetic displacement measurements along the road that crosses the moving debris body undertaken since 1977 by the Icelandic Road Authorities, have revealed displacements of up to 1 ma-1. Figure 1: a) Location of the sites in Iceland b) Location of the debris covered glacier (1) and rock glaciers (2-11) at Hólar. Debris covered glacier and rock glaciers at Hólar The debris covered glacier and rock glaciers are located at the central part of the Tröllaskagi peninsula (65°40'N, 19°W) close to Hólar at an altitude of 900-1200 m.a.s.l. The debris covered area of the glacier is in the range of 70-80% and up to several metres thick. The debris layer is therefore protecting the glacier surface from melting. Figure 5: a) Location of the moving debris accumulation at Almenningsnöf b) Orthophoto of the debris accumulation The measurements were initiated due to observed damage on the road. The greatest velocities are found in the SW part with an average around 0.6 ma-1. In the mid section the velocities are around 0.2 ma-1, while they are around 0.1 ma-1 at in the upper part of the body. At some places the movements show rather a discrete than continuous pattern with zones where the velocity changes dramatically over small areas. In figure 6b the velocity at both sides of a crevasse is shown, with displacements of 0.5-0.6 ma-1 on one side and 0.2 ma-1 on the other. Figure 2: a) Oblique view of the debris covered glacier at Hólar b) Photo from the surface of the same glacier (location marked in a). The velocity of the debris covered glacier and the rock glaciers in the Hólar area average from 0.14 ma-1 to 0.67 ma-1. Based on the surface age results all landforms are suggested to have developed during the late-Holocene cooling period, with ages from around 1500 yr, 3000 yr to 5000 yr. These surface age estimates coincide with data from moraine dating nearby (Stötter 1999) and Holocene climatic development in the North Atlantic region (Karlén 1988). Figure 6: a) Yearly displacement from 1985 to 1994 for the debris covered glacier at Almenningsnöf b) zone of great velocity differences around a crevasse-looking feature References Karlén, W., 1988. Scandinavian glacial and climatic fluctuations during the Holocene. Quaternary Science Reviews, 7: 199-209. Kääb, A. and Vollmer, M., 2000. Surface Geometry, Thickness Changes and Flow Fields on Creeping Mountain Permafrost: Automatic Extraction by Digital Image Analysis. Permafrost and Periglacial Processes, 11: 315-326. Stötter, J., Wastl, M., Caseldine, C. and Häberle, T., 1999. Holocene paleoclimatic reconstruction in northern Iceland: approaches and results. Quaternary Science Reviews, 18: 457-474. Wangensteen, B., Guðmundsson , Á., Eiken, T., Kääb, A., Farbrot, H. and Etzelmüller, B. (in press). Surface displacements and surface age estimates for creeping slope landforms in Northern and Eastern Iceland using digital photogrammetry. Geomorphology. Figure 3: a) Annual displacement from 1985 to 1994 for the debris covered glacier at Hólarb) age estimates based on the same velocity field