STEINSKRED

The field trip of the 3rd Slope Tectonics conference visits areas of past rock slope failures and present-day unstable rock slopes and aims to discuss the structural and geological conditions of these sites, the morphologies and tectonic fabrics induced by slope movements and the role of glaciers, isostatic uplift and major faults in the development of rock slope failures.

The 3rd Slope Tectonic Conference arranged at the Geological Survey of Norway on September 8.-12. 2014, follows the 2nd Slope Tectonic Conference organized at the Geological Survey of Austria in 2011 and the 1st Slope Tectonic conference organized at the University of Lausanne, Switzerland in 2008. It stands in an international tradition and a total of 56 contributions will be given on rock slopes affected by slope tectonic processes from 20 counties including Argentina, Austria, Canada, Chile, China, Czech Republic, France, Iceland, Italy, Japan, Kazakhstan, Mongolia, Morocco, Nepal, Norway, Pakistan, Po-land, Scotland (UK), Slovakia, and Switzerland.

The Stuoragurra Fault Complex (SFC) constitutes the Norwegian part of the larger Lapland province of postglacial
faults in northern Fennoscandia. The 90 km long SFC consists of three separate fault systems; the Fitnajohka Fault
System in the southwest, the Máze Fault System in the central area and the Iešjávri Fault System to the northeast.
The distance between the fault systems is 7–12 km. The faults dip at an angle of 30–75° to the SE and can be traced
on reflection seismic data to a depth of c. 500 m. Here we present data from trenching of different sections of the
fault complex. The trenching reveals deformed overburden in all 8 sites, and inclusions of peat and organic bearing
soil in the deformed and partly overrun loose deposits on the footwall in all but one site.
Radiocarbon dating of organic matter located in buried and severely deformed sediment horizons indicates late
Holocene ages for the (final) formation of the different fault segments, more specifically that the Máze, Fitnajohka
and Iešjávri (Guovziljohka) Faults formed during earthquakes younger than 600 years, younger than 1,300 years and
younger than 4,000 years BP, respectively. The youngest age is at the Masi (Mazé) site, where plant macrofossil data
from the buried sediments suggest an early to late Holocene vegetation cover. The reverse displacement of c. 9 m
and fault system lengths of 14 and 21 km of the two southernmost fault systems indicate a moment magnitude of c. 7
on Richter’s scale if just one rupture event is associated with each of these systems. The fault rupture with length and
height of fault scarps, and injections and throw-out of angular boulders and wedges of fault breccia reaching up to
15–20 m away from the fault scarp give the most distinct expressions of the associated earthquake magnitude with
the SFC. A total of c. 60 landslides, some of these possibly earthquake-induced, has been recorded along the SF.
Initial breakage or fracturing of bedrock with a potential to lead to larger rock avalanches are also recorded at a few
places in or close to the fault zone.

The Stuoragurra Fault Complex (SFC) constitutes the Norwegian part of the larger Lapland province of postglacial
faults in northern Fennoscandia. The 90 km long SFC consists of three separate fault systems; the Fitnajohka Fault
System in the southwest, the Máze Fault System in the central area and the Iešjávri Fault System to the northeast.
The distance between the fault systems is 7–12 km. The faults dip at an angle of 30–75° to the SE and can be traced
on reflection seismic data to a depth of c. 500 m. Here we present data from trenching of different sections of the
fault complex. The trenching reveals deformed overburden in all 8 sites, and inclusions of peat and organic bearing
soil in the deformed and partly overrun loose deposits on the footwall in all but one site.
Radiocarbon dating of organic matter located in buried and severely deformed sediment horizons indicates late
Holocene ages for the (final) formation of the different fault segments, more specifically that the Máze, Fitnajohka
and Iešjávri (Guovziljohka) Faults formed during earthquakes younger than 600 years, younger than 1,300 years and
younger than 4,000 years BP, respectively. The youngest age is at the Masi (Mazé) site, where plant macrofossil data
from the buried sediments suggest an early to late Holocene vegetation cover. The reverse displacement of c. 9 m
and fault system lengths of 14 and 21 km of the two southernmost fault systems indicate a moment magnitude of c. 7
on Richter’s scale if just one rupture event is associated with each of these systems. The fault rupture with length and
height of fault scarps, and injections and throw-out of angular boulders and wedges of fault breccia reaching up to
15–20 m away from the fault scarp give the most distinct expressions of the associated earthquake magnitude with
the SFC. A total of c. 60 landslides, some of these possibly earthquake-induced, has been recorded along the SF.
Initial breakage or fracturing of bedrock with a potential to lead to larger rock avalanches are also recorded at a few
places in or close to the fault zone.

In this report we have assessed some of the characteristics of the 248 rock avalanche deposits (rock slope
failure deposits and their related source areas) inventoried in Norway up to date. These pre-historic and
historic rock avalanche deposits are mostly located in the North (Troms and Finnmark counties) and in the
South (Vestland and Møre og Romsdal counties) of Norway. Their spatial distribution is clearly correlated to
relief conditions. The lithologies involved in the rock avalanche events in the North and the South differ, which
can be related to different dominant lithologies in both regions. The identified deposits are present on land,
in fjords and lakes, or a combination of those. Some are very well preserved, while others have been eroded
by rivers or buried by fluvial deposits. Our work shows that the mobility of the rock avalanches is correlated
to the slope conditions. A preliminary result is that mobility on average decreases with increasing slope angle.
This relation, that has not been documented in previous studies, could be related to energy loss under
particular topographic conditions in deeply glacially eroded valleys. While we investigate a significant number
of past rock avalanche events in this report, systematic mapping at the national scale is likely to (i) shed light
on the uncertainties identified in this report, (ii) provide data with the potential to improve the understanding
of rock avalanche occurrence and dynamics, and (iii) generate baseline data for improved assessment of
run-out length of future rock avalanche scenarios.