The Nordnes rockslide in northern Norway poses a threat to local settlements
along the nearby fjord due to its potential of generating tsunamis.
Therefore, a monitoring program was initiated in 2007. Evaluation
of the resulting monitoring data is expected to provide important
contributions to the understanding of the sliding mechanisms.
This paper focuses on statistical analyses of continuous laser and
crackmeter measurements at the Nordnes rockslide during a period
of 16 months. Annual linear displacements and seasonal fluctuations
were estimated from time series of 3 lasers and 10 crackmeters.
Results from the analyses show that the north-westernmost part of
the area has the largest movement of more than 5 cm per year, which
makes this part the most critical in terms of generation of a rapid
rockslide. The amplitudes of the seasonal fluctuations estimated
from crackmeter time series were approximately 0.5 mm. The largest
displacements clearly occur in autumn and early winter with a stagnation
or retreat phase in spring and summer. Thus, the movements are not
increased during snowmelt which is a normal seasonal characteristic
elsewhere. Although the temperature changes have a significant effect
on the observed displacements, the seasonal variations could not
fully be modelled with temperature terms in the regression models
suggesting that there are other additional controlling factors. The
rockslide is localized in arctic and periglacial conditions, and
the documented seasonal variations are interpreted to be linked to
effects of deformations caused by seasonal frost and permafrost.
Prediction intervals for future displacements were also derived from
the current time series. These prediction intervals are considered
useful for the evaluation of future measurements and may serve as
basis for defining alert thresholds for possible future early warning
systems.