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37
SAMC
o
T • Annual report 2012
by manual measurements. The retreats of the bluff in
Fredheim vary widely from season to season in some
parts, while the retreat has been steady in other areas.
The coastal retreat at the site has been monitored (not
continuously) since 1986 and the retreat rate has varied
from year to year. Erosion rates are calculated based on
the manual measurements from three different studies.
In 2012, the expected lifetime for the houses threatened
by erosion hazard was estimated based on the calcu
lated erosion rates on the coastal line.
Between 2011 and 2012, the erosion rate was approxi
mately 30 cm. The study shows that there are varia
tions in erosion rates between the erosion edge and the
individual houses. This can largely address the erosion
mechanisms of Fredheim. Previously, it was believed
that the erosion was strongly linked to wave erosion,
but the recent findings indicate that this might not be
the case. Waves are a contributing factor, essentially
as a carrier of already eroded soils. The main erosion
process is melting and sliding of permafrost soil
blended with local water (Fig. 39). In these channels,
fine grains are washed out by the local water, causing
the bluff and coastline to become more unstable in this
area. This process also contributes to instability in the
area between channels due to reduced lateral support.
The erosion rates vary significantly from year to year.
This variation can be seen in comparisons related to air
temperature, precipitation and the length of the ice-free
season, which changes from year to year. Regarding
annual variations, erosion rates have only been
measured from one year to the next during 2010-2011
and 2011-2012. For these measurements, there is
a change in the erosion rate when the erosion rate in
Fig. 36. Vestpynten temperature data.
Fig. 37. Stratification observed in the front of the bluff at
Vestpynten.
Fig. 38. Presentation of DGPS measurements, 2010,
2011 and 2012 (Tangen and Justad, 2012).
Fig. 39. Zone with water channels and leached soil
Photo: Evangeline Sessford