Jökull - 01.01.2009, Page 89

Reviewed research article
Slope creep in East Iceland observed by satellite radar
interferometry
Sigurjón Jónsson
Institute of Geophysics, ETH Zürich, Sonneggstr. 5, 8092 Zürich, Switzerland1
sj@erdw.ethz.ch
Abstract — Numerous unconsolidated deposits can be found on slopes in East Iceland that exhibit charac-
teristics of slope movement. While a few of these slopes have been known to be actively creeping in the past
decades, no information has been available about the current activity. In this study I surveyed a large part
of East Iceland for possible ongoing slope creep using satellite radar interferometric imaging. A total of 44
radar interferograms were processed using data from the European radar satellites ERS-1, ERS-2, and Envisat,
spanning different time-periods during 1993–1999 and 2004–2005. At one site, Þófi in Seyðisfjörður, ground
cracks were discovered in 2000 and GPS measurements in 2001–2002 revealed that these deposits were mov-
ing at rates of up to 33 cm/year. No suitable ERS radar data exist from 2001–2002, but interferograms from
1998 and 1999 show up to 10 cm/year displacement-rate in this area, while interferograms from 1995–1997
and 2004–2005 exhibit no signs of displacement. This shows that the Þófi deposits started creeping two years
before surface cracks were discovered and that the movement is episodic. In my search for other active slope
displacements in East Iceland I found more than ten locations of previously unknown slope creep. The most
prominent displacements were discovered in Vopnafjörður where the deposit creep shows variations in both
displacement rate (up to 1 m/year) and areal extent during the observation period, which further demonstrates
the episodic behavior of unstable slopes in East Iceland.
INTRODUCTION
Numerous unconsolidated slope deposits have been
geomorphologically described and catalogued in East,
central-North, and several other regions in Iceland
(Jónsson, 1976; Guðmundsson, 1990). The origin of
these deposits has been a subject of a considerable de-
bate during the past decades. Many have interpreted
them as being deposits from sudden catastrophic slope
failures or rock avalanches (e.g. Þórarinsson, 1959;
Jónsson, 1976). In resent years, however, another in-
terpretation has been gaining ground that links these
deposits to active and inactive ("fossil") rock glaciers
(Guðmundsson, 2000). The history of past mor-
phological investigations and interpretations has been
summarized by Guðmundsson (1995a).
After active slope creep was discovered near the
towns of Seyðisfjörður and Neskaupstaður in East Ice-
land, GPS measurements showed up to 33 cm/year
displacement rate in Þófi in Seyðisfjörður and even
higher rates above Neskaupstaður (Jensen and Jó-
hannesson, 2002; Jensen and Hjartarson, 2002).
These GPS results, among other things, led to the
initiation of this project focussing on using satellite
radar interferometry (InSAR) to study unstable slopes
in Iceland, as InSAR has been successfully applied
to monitor unstable slopes at many locations around
the world (e.g. Fruneau et al., 1996; Rott et al., 1999;
Colesanti et al., 2003). The main goals of the project
were (1) to investigate the feasibility of InSAR to
detect and monitor slope movement in Iceland, (2)
1Now at King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia (sigurjon.jonsson@kaust.edu.sa)
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