ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

the xx- Century and its implications on soil degradation.
Predominant in Alentejo, the montado is an extensive
agroforestry system based on fodder production and grazing,
cereal crops, evergreen oak trees (Quercus suber
and/or Quercus rotundifoliai and olive trees exploitation,
associated with latifundium. During the xx- Century, the
system suffers pulses of injuries and transformation or substitution
(intensification of the cereal production, overgrazing,
cutoff of the trees, introduction of exotic species like
Eucalytus ).
The causes more frequently evoked to explain the spatial
variation of soil degradation in Alentejo are the land use
practices and the mismanagement of soil and vegetation.
But, a particular attention needs also to be paid to the impact
of the climate evolution, particularly of the variability
in the precipitation seasonality, in the rainfall intensity and
concentration, and in the frequency of drought spells. In
Alentejo, historical changes in land use and climate involving
soil erosion are reflected by geomorphological, runoff
and soil capability changes. At diferentes scales, from
the extrapolation of the results of experimental studies of
the effect of crops and rotation on run-off and soil erosion,
essentially at Mertola-Vale Formoso, from the analysis of
sediments deposition in reservoirs, from the observed
stream discharge, and from geomorphological evidences,
we try to estimate the long term variations of soil erosional
processes in Alentejo during the xx- Century. The overall
objective is to show that the planning of the rural development
in the inner Alentejo should not ignore the interactions
of the history of land use and climate which have determined
the actual soil suitability for agriculture and forestry.
The effects of these interactions determine the future
potentialities to be taken into account in a decision support
system on rural land resources and land use management.
The poster shows the diferents aspects of the assessment of
the erosional impact of land use change in Alentejo during
the xx- Century (1886-1995), with an exemplification in
the councils of Moura and Barrancos. The prime aim was
to express the evolution of the spatial variations of the risk
of erosion and to indicate sustainable land use. The results
will be designed to provide an important input to the formulation
of conservation schemes. It is organized in three
parts which present the synthesis of:
- the diacronic analysis of the land use (evolution in an
openfield for cereals crops; change in area and density of
tree cover; importance of abandoned fields ...; identification
of critical fases for potential soil erosion);
- the evolution of climate in Alentejo during the xx­
Century (total precipitation and variability, rythm, water
stress and rainfall intensity) and its influence on vegetation
and on the variations in the type, magnitude and frequency
of water erosion processes.
- a comparative study of the assessment of land use capability
and risk of soil erosion, using three particular moments
in the xx-Century: at the beginning of the century,
in the 1960's and at present.
166
ERIC J. FIELDING
.Tectonic geomorphology of the Tibetan Plateau and
Himalaya using high-resolution digital topography
from interferometric analysis of Shuttle radar imagery
Jet Propulsion Laboratory, California Institute of Technology,
4800 Oak Grove Dr., Pasadena, CA 91109, U.S.A.
The interior of Tibet is characterized by shallow slopes because
the lack of long-wavelength relief and dry climate
preclude fluvial and glacial dissection, and because late
Cenozoic tectonics have not deformed the surface. In contrast,
the active tectonics and wetter climates of the
northern and southern margins of Tibet, the Kun Lun and
the Himalaya, generate high relief and steep slopes. In the
moderately dry Kun Lun, alluvial deposits are offset by displacement
on the active Altyn Tagh fault. In the Himalaya,
especially on the monsoon-washed southern slopes,
rapid erosion can remove efficiently small geomorphic features
such as fault scarps and glacial moraines.
New high-resolution digital topography has been produced
for portions of a transect across the Tibetan Plateau
and the Himalaya by interferometric processing of radar
data. Analysis of this dataset provides new information on
the geomorphic response to variations in denudation rates,
relief, structure, and lithology. The present topography
presumably represents a balance between the tectonic and
erosion processes, and the latter have been affected by
Quaternary climate changes. The north face of Everest has
a fairly uniform hillslope angle of about 42° (with a -80 ill
window size), which may be controlled by the shallow
northward dip slope of the mylonitic schists, or may represent
a maximum sustainable slope for those lithologies. Several
other peaks and ridges north of Everest have more
uniform, but shallower, slopes in the range of 30-35°, which
may indicate either rocks of lower strength or less rapid
denudation. Future geologic mapping in this area will help
to constrain the lithologic contrasts and allow comparisons
to the geomorphic characteristics.
Interferometric processing of suitable pairs of synthetic
aperture radar (Sar) images can produce a high-resolution
digital elevation model (Dern). Airborne systems can provide
the highest resolution Dems, but spaceborne Sar provides
greater data coverage, especially in remote regions
such as the Himalaya. I have derived Dem's for the Kunlun,
interior of Tibet and the Everest area of the Himalaya.
I used a pair of images from the interferometry phase of
the October 1994 Shuttle Imaging Radar (Sir-C) flight.
The extreme relief in the Himalaya causes some problems
for topographic measurements, even with radar. The Sir-C
radar instrument can be steered to different incidence angles,
and used a 51° incidence angle (measured from the
vertical) for these data which works much better in highrelief
areas than other radar systems, such as the Ers-1 Sar
(21° incidence angle). The Dem extraction used the Lband
(-24 ern wavelength) channel of the radar. The Himalaya
Dem has a grid spacing of 20 x 20 m, and covers an