Geoscience Reference
In-Depth Information
and sets of steep near-vertical joints. Tension
cracks on the surface behind the slope face tend
to open parallel to the steeply dipping natural
joints. Currently the Swiss Seismological Service
have installed a network of surface seismographs
to monitor local activity. This has proved useful
in identifying fracturing within the underlying
rock mass (Eberhardt et al. 2001). Monitoring
will be extended to included borehole installa-
tion of microseismic triaxial transducers around
the developing shear plane. The movements
are being monitored by geodetic survey and an
extensiometer gauge, which will enable the brit-
tle fracture development of the rock mass to be
assessed. Based on observations of the current
instability the local authorities have been able to
act in advance of another failure, i.e. to realign
the road and railway to avoid the impact of
potential new landslides.
Case Study 2.3, which focuses on the sedi-
ment related problems following the 1980 Mount
St Helens eruption, provides additional details
on remediation. It is clear from the Mount
St Helens example and the examples just dis-
cussed that there are three phases in which envir-
onmental sedimentology can play a significant
role:
1 hazard assessment and mapping;
2 monitoring of mountain sedimentary processes;
3 prediction of long-term sediment delivery
from disturbed mountain environments and
design of appropriate remediation measures to
deal with the sedimentation problem.
debris flows, and microscale hydraulic modelling
of sedimentary systems.
2.6.1 Considering future climate change scenarios:
debris flows in the Alps
Many mountain environments are influenced by
glacier and permafrost hazards, which present
a direct threat to infrastructure, settlements and
human life in high-altitude and high-latitude
mountain areas. Global warming is affecting the
thermal stability of surface and subsurface ice,
and glacier and permafrost equilibrium limits
are shifting in response to this general trend
(see Chapter 1). The situation is made worse as
development pressures in mountain areas are
forcing human settlement and activities fur-
ther into the mountain cryospheric zone. For
example, under the prediction of a warming
scenario for the Alps the following are all likely
consequences (Zimmermann & Haeberli 1992;
Haeberli 1995):
1 greater frequency of outburst floods and
glacier hazards;
2 permafrost degradation and slope instability
- increased debris flow activity;
3 decline in material strength of foundations of
high mountain buildings;
4 damage to reservoir systems (damage to infra-
structure) and increased sedimentation rates
(reduced storage capacity).
More generally the impact of such warming is
a range of glacier-related hazards that include:
glacier lake outburst floods; rock and ice ava-
lanches; deep seated instability; and retreat of
glacier and permafrost limits. Many of these
have important impacts on the sedimentology of
mountain environments, resulting in enhanced
rates of debris supply, extensive flood deposits and
large-scale mass movements. Examples include
the increased frequency of rock avalanches in
relation to permafrost degradation in glacier
environments: the Brenva Glacier, Mont Blanc
in 1997 (Bottino et al. 2002; Haeberli et al. 2002)
and the September 2002 Kolka-Karmadon
rock and ice avalanches and mudflows in the
Caucasus Mountains of Russia (Kääb 2002;
Kääb et al. 2003).
2.6
FUTURE ISSUES
All environmental and economic indicators
suggest that over the next few decades moun-
tain environments will become more stressed
and erosion and environmental degradation will
become greater problems. This section con-
siders how sedimentology can provide useful
tools for remediation of geomorphological prob-
lems, thus enabling mountain life to continue in
a changing environment. The two main examples
include: predictions involving the evaluation of
climate change scenarios and the occurrence of
Search WWH ::




Custom Search