SURFACE DISPLACEMENTS AND VOLUME
CHANGES FOR SOME DEBRIS COVERED
GLACIERS AND A MOVING DEBRIS BODY AT
THE TRÖLLASKAGI PENINSULA, NORTHERN
ICELAND, BY THE USE OF DIGITAL
PHOTOGRAMMETRY
B. Wangensteen (1), Á. Gudmundsson (2), T. Eiken (1), A. Kääb(3),
H. Farbrot (1) and B. Etzelmüller (1)
(1) Department of Geo Sciences, University of Oslo, P.O.Box 1047 Blindern, N-0316 Oslo,
Norway. (2) Jardfrædistofán Geological Services, Reykjavik, Iceland. (3) Department of
Geography, University of Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich,
Switzerland. (bjorn.wangensteen@geo.uio.no)
The Tröllaskagi peninsula is located between Skagafjördur and Eyafjördur on Northern Iceland between 65o 20’ - 66o 10’N and 18o - 19o 30’ W. In this study, measurements of the displacement field and volume change of a moving debris body and some
debris covered glaciers are presented.
The debris covered glaciers are located at the central part of the Tröllaskagi peninsula (65o 40’N, 19o W) at an altitude of 900-1200 m.a.s.l. Geophysical and modeled
results by other researchers in the project show that this is at and above what seems
to be the lower limit of sporadic permafrost. Simple extrapolation from the meteorological station in Hólar (140 m.a.s.l.), 4-7 km away from the glaciers, gives a MAAT
of about -2.5o C at the front of the debris covered glaciers. The debris covered areas
of the glaciers are in the range of 70-80% and up to several metres thick. The debris layer is hence protecting the glacier surface from melting and produces a much
greater glaciated area than would otherwise be the case under the same conditions. By
visual inspection the debris cover shows signs of secondary creep related to permafrost
processes. The displacement fields are measured based on cross-correlation matching
of othophotos from 1960,1985 and 1994 derived from digital photogrammetry. Volume changes are calculated based on the differences between DTMs automatically
constructed by the use of digital photogrammetry. The magnitude of the surface displacements indicates that it is permafrost creep rather than glacier flow that dominates
the cause of the movements.
The moving debris body is located at the road along the coast to Siglufjördur at the
northern tip of the Tröllaskagi peninsula (66o 10’N, 19W). At the meteorological station at Saudanes (20 m.a.s.l), just 5 km north of the debris body, the MAAT is 3.6o C.
The moving debris body is situated between 0 and 300 m.a.s.l. and one should not expect a MAAT under +1.8o C based on simple extrapolation and, hence, no permafrost
conditions. Geodetic displacement measurements undertaken since 1977 by the Icelandic road authorities along the road that crosses the moving debris body, have revealed displacements of up to 1 m/year. The measurements were initiated due to observed damage on the road. The movements show rather a discrete than continuos
pattern with zones where the velocity along the road changes dramatically over small
areas. This pattern is also confirmed by the cross-correlation matching of four sets of
orthophotos from 1955, 1977, 1985 and 1994. The velocities measured by the use of
orthophotos are in agreement with the GPS measurements. In the same way as for the
first location, volume changes are also calculated from DTMs of the respective years.
The cause of the movement is unsure, as glacier and permafrost factors can be ruled
out due to the location. The initiation of the movement on the other hand could have
started in times where the conditions were different. Soil and/or hydrological factors
could have supported further movement.