Suchergebnisse

Abstract. Based on an inventory of 69 dams formed by rock slope
failures in southwestern Norway and published inventories from other parts
of the world, we developed semi-empirical relationships linking the maximum
dam height (HD.max in metres) to dam volume (VD in
106 m3) and other relevant parameters such as valley width
(WV in metres) or dam area (AD in square kilometres). Power laws are
obtained for HD.max=f(VD) and HD.max=f(VD, WV),
while a linear relationship links HD.max to the ratio
VD∕AD. For dams in southwestern Norway, the linear relationship
HD.max=1.75×VD/AD has the least uncertainties and
provides the best results when comparing predicted dam heights with a validation
dataset composed of existing dams in northern Norway and numerically
modelled dams for possible rock slope failures. To assess the stability of
future dams, we use the predicted dam heights in the dimensionless blockage
index (DBI) and relating this index to the probability of dam failure derived
from our dataset and other published databases on landslide dams. This study
underlines the potential of semi-empirical relationships for assessing dam
height and stability that needs to be included in preliminary hazard and
risk assessment for unstable rock slopes, because damming of a river is an
important secondary effect of landslides due to upstream flooding and
possible outburst floods in the case of dam failure.

Abstract. We characterize and compare creep preceding and following
the complex 2011 Pampahasi landslide (∼40 Mm3±50 %) in the city of La Paz, Bolivia, using spaceborne radar
interferometry (InSAR) that combines displacement records from both
distributed and point scatterers. The failure remobilized deposits of an
ancient complex landslide in weakly cemented, predominantly fine-grained
sediments and affected ∼1.5 km2 of suburban development.
During the 30 months preceding failure, about half of the toe area was
creeping at 3–8 cm a−1
and localized parts of the scarp area showed
displacements of up to 14 cm a−1. Changes in deformation in the 10 months
following the landslide demonstrate an increase in slope activity and
indicate that stress redistribution resulting from the discrete failure
decreased stability of parts of the slope. During that period, most of the
landslide toe and areas near the head scarp accelerated, respectively, to
4–14 and 14 cm a−1. The extent of deformation increased to cover most, or
probably all, of the 2011 landslide as well as adjacent parts of the slope
and plateau above. The InSAR-measured displacement patterns, supplemented by
field observations and optical satellite images, reveal complex slope
activity; kinematically complex, steady-state creep along pre-existing
sliding surfaces accelerated in response to heavy rainfall, after which
slightly faster and expanded steady creeping was re-established. This case
study demonstrates that high-quality ground-surface motion fields derived
using spaceborne InSAR can help to characterize creep mechanisms, quantify
spatial and temporal patterns of slope activity, and identify isolated
small-scale instabilities; such details are especially useful where
knowledge of landslide extent and activity is limited. Characterizing slope
activity before, during, and after the 2011 Pampahasi landslide is
particularly important for understanding landslide hazard in La Paz, half of
which is underlain by similar large paleolandslides.