International Archives of Photogrammetry and Remote Sensing. Voi. XXXII Part 7C2, UNISPACE III. Vienna. 1999
100
I5PR5
UNISPACE in - ISPRS/EARSeL Workshop on
“Remote Sensing for the Detection, Monitoring
and Mitigation of Natural Disasters”
2:30-5:30 pm, 22 July 1999, VIC Room B
Vienna, Austria
2.3 Volcanoes
Volcanoes are distributed around the world in zones, which
geologists refer to as plate boundaries. In smaller clusters, they
occur also within geological plates or continents, mainly along
deep seated geological graben structures and fault systems. We
differentiate between active volcanoes, dormant volcanoes and
extinct volcanoes. This distinction alone bears already some risk:
Pinatubo, the volcano that exploded in the Philippines in June
1991 was regarded as dormant. Its last eruption dated back to the
15 th century. 500 years is a very short interval in the life of a
volcano with an age of more than one million years. In this
regard, we even have to regard our volcanoes in Germany as a
potential danger, since some of which show slight degassing and
are morphological very prominent. Their last eruptions took
place only 11.000 years ago.
There is a number of risks involved by dwelling in the vicinity of
an active volcano. Not only the eruptive products, pyroclastic
flows, tuffs, lava flows and lahars are threatening life and
infrastructure, but also associated earthquakes, tsunamis and the
silent death of CO 2 -eruptions as happened on Nyos-volcano in
Cameroon in 1986. The huge methane content in Kivu-Lake at
the Zaire-Burundi border is another constant threat to the
population living at its shore (TIETZE, K.1992).
In the aftermath of volcanic eruptions the deposition of lahars
can have catastrophic dimensions as could be seen on the flanks
of Pinatubo in the Sto. Tomas basin and the Sacobia watershed,
or on Mt. St. Helens.
2.4 Active faults and earthquakes
Optical as well as radar imagery are excellent tools to map active
faults. If compared with information on the location of seismic
hypo- and epi-centres areas prone to earthquakes can be
delineated. Observations from LANDS AT-TM images in the
Himalayan mountains of Nepal revealed a clear connection
between of active faults, associated with earthquakes, and the
occurrence of large landslides. Effects of earthquakes of the kind,
which devastated Mexico City in 1986 can be mitigated by
mapping large basins and analyse the underground sediments
with conventional geological methods.
3. THE POTENTIAL OF REMOTE SENSING IN
GEOLOGICAL HAZARDS MONITORING
Modem remote sensing teclmologv provides excellent
opportunities to observe geodynamic processes. However, the
sensors and platforms to be utilised have to be adequate to the
problem addressed. In many cases, where fast processes are
involved, a high repetition rate is essential in monitoring the
event. This is currently only the case with spatially low resolution
weather satellites.
3.1 Erosion
Optical sensors, spacebome or airborne, can be employed to map
repeatable the area affected by erosion. The effects along
coastlines can be very dramatic. We found changes in coastline
erosion and sedimentation in the magnitude of several kilometres
in the vicinity of Jakarta, on the island of Java/Indonesia but
wind erosion in the northern parts of France, Belgium and
Germany have been found to be quite severe in places. Recently,
much attention is drawn to landslides. Here again, we have to
differentiate between several types of landslides. Large to
medium sized landslides can be detected on SPOT, IRS and
LANDSAT-TM images and in a combination of RADAR-
images and Digitial Terrain Models (DTM) (GUILLANDE, R. et
al. 1991; LEROI, E. et al. 1992), smaller ones on air-photos. Soil
creep, which can accelerate during heavy rainfalls are extremely
difficult to assess. Mapping using airborne laser-scan technology
is still expensive and needs to be flown repeatedly. The example
of subtle terrain changes over underground mines in the northern
part of Germany, however, demonstrate the value of this method
(KUEHN, F. et al. 1999). Radar interferometry even from
satellite orbits can give excellent results in the cm-range of
displacement (MASSONET, D. 1999). However, vegetation
cover, which is abundant in the moderate and climates and
especially in tlie humid tropics makes it impossible so far, to
detect slight topographical changes. The use of permanent corner
reflectors provides only movements of the particular reflector,
but this can be done in the magnitude of cm as well. Longer radar
wavelengths, however, might not be affected so much by
vegetation cover, but can only be used for landslides with
considerable dislocations. Those, in general are known already.
Among all the remote sensing data, optical data, especially air-
photos can provide the largest amount of information. Combined
with a differentiated digital terrain model, thorough field survey
and further geologic and climatic data, the air-photo
interpretation will definitely yield the best results. There has been
observed a thermal anomalous behaviour prior to sliding
recently, but research lias not been carried out to explain the
reasons behind it.
3.2 Land-degradation
Land degradation monitoring and early warning can be
successfully accomplished with satellite sensors, operating in the
visual and short-wave infrared. First encouraging results liave
been achieved during the Sahelian drought during the early 70-ies
in Burkina Faso and Niger. Monitoring or early wanting systems,
however, seem to be inadequate to the modern technological
standards. In our opinion, the lack of medium resolution satellite
data in real-time in the affected countries is felt very severely.
The VegSat concept, developed by Bundesansalt fur
Geowissenscliaften und Rohstoffe - (Federal Institute for
Geosciences and Natural Resources), Hannover, FRG, offers a
solution, but it needs a concerted effort to put such a system into
reality (BANNERT, D. 1980).
3.3 Volcanoes
