Geoscience Reference
In-Depth Information
The Kolka-Karmadon rock avalanche began
on the evening of 20 September 2002 high on the
peak of Dzimarai-khokh. Several million cubic
metres of ice and debris fell on to the Kolka
glacier tongue, shearing off the front of the glacier
before crossing the Maili glacier. Travelling at
around 100 km h
−1
the avalanche picked up
lateral moraines and valley-bottom sediments
before running out and halting approximately
18 km from the source, where approximately
80
Landslide type and cause also differed over
time. Following retreat of the glaciers after
the Last Glacial Maximum there followed a
phase of increased slope instability (11,500 to
8500 cal. yr BP) involving large translational
bedrock slides in the dolomitic slopes and
complex movements (both rotational slides and
flows) affecting the underlying pelitic forma-
tions. A second phase of enhanced activity was
also identified around 5800-200 cal. yr BP, when
slope processes were dominated by mainly rota-
tional slides and flows. The mechanisms for such
activity vary. In the earlier slides high ground-
water levels related to increased precipitation
and/or permafrost melt were probably import-
ant. In the second phase, many of the slope
movements were reactivations of earlier land-
slides and probably were triggered by increased
precipitation. Studies of this kind are valuable
when considering potential impacts of future
climate change because although patterns of
historical landscape instability can be linked to
climate, and to some extent these fit with gen-
eral patterns of slope movements across Europe,
non-climatic factors (e.g. geological-structural
factors and changing human land-use) also have
a role to play and should not be excluded from
the analysis.
10
6
m
3
of ice and debris were deposited and
after which a mudflow approximately 300 m
wide continued for another 15 km down the con-
fined valley. A total of 120 people were killed in
the catastrophe and since the event the deposits
continue to influence sedimentary processes in
the valley system. Rivers were dammed by the
avalanche deposits, which caused the forma-
tion of lakes estimated to be over 10
×
10
6
m
3
in volume. These posed a considerable danger
to settlements down-valley owing to the risk of
dam-break flooding.
Because of the remote nature of the environ-
ments in which these high-mountain processes
operate, rapid assessment of glacier hazards
is needed through the use of remotely sensed
data. Rapid imagery from ASTER (Advanced
Spaceborne Thermal Emission and Reflection
Radiometer) provides 15 m resolution imagery,
which is updated regularly every 16 days but this
can be shortened to 2 days where needs demand
(Kääb et al. 2002). From these data digital
elevation models (DEMs) can be generated,
which are essential for assessing the dynamic
changes in topography that characterize these
rapid sedimentary events.
The above example illustrates how recent
environmental change is having an impact on
mountain hazards. It should be recognized, how-
ever, that the incidence of mountain hazards also
varies over much longer cycles. For example,
Soldati et al. (2004) examine the relationship
between the temporal occurrence of landslides
and climatic changes in the Italian Dolomites
since the last glacial stage (Würm). Increases
in landslide activity were identified correspond-
ing to the boundaries between the Late-glacial
and Holocene and the Atlantic and Sub-boreal.
×
2.6.2 Microscale modelling
Understanding sedimentation problems in
mountain environments is difficult because prob-
lems evolve over several decades or centuries and
the main governing processes operate at scales
that cannot be measured easily. Microscale model-
ling provides a valuable tool for the environ-
mental sedimentologist to investigate large-scale
sedimentation processes in mountain-valley sedi-
ment systems. Microscale loose-bed hydraulic
models are very small-scale and conventionally
have been used to evaluate channel designs
on large river systems (Gaines & Maynord
2001). Typically model studies are carried out
to determine channel response to engineering
structures and identify overall flow patterns
within the fluvial system. A basic model consists
of a hydraulic flume, a rigid channel insert to
