ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

part of the basin. These deposits are divided into three chronological
units (Miocene to Pliocene in age) covering an
area of about 4000 km'. There is an important fracturing at
the outcrop scale, with several maxima, not very well defined,
striking 020-030, 040-050, 060-070, 140-150 and 160­
170 (Fig. A).
We utilised a satellite image to determine the fracture pattern
of the Neogene rocks at medium scale. To perform
this study, we use an image (200-31) from the Landsat 5
satellite with Thematic Mapper sensor taken in September
of 1984 at sun time 10.02. With the selected area we try
different combinations of three bands and the best visual
quality was obtained with a false colour image utilising the
bands 2,4 and 5 (in blue, green and red, respectively). Because
of the big size of the image we decided to make 24
subscenes (4 rows and 6 columns) for an easiest and more
detailed manipulation. After doing a linear contrast stretch
of the subscenes a visual study was made and 2.547 lineaments
were mapped. The high number of lineaments that
we found conditioned the use of an automatic exploration
program to determine the following parameters for each
one of the lines obtained: the X and Y coordinates from
the first and last pixel, its length in pixels, the slope of each
line and the goodness of the fitting to a straight with the
same slope. From this file the length and orientations of
the studied fractures are represented and statistical analysis
of this data can be carried about. The knowledge of the X
and Y coordinates of the first and last point of each line allows
the differentiation in areas or domains to be studied
and analysed independently and consequently to establish
comparisons among them.
Lineaments are distributed throughout the studied area.
Its absolute orientation maximum strikes 060-070, and several
relative maxima strike 100-110 and 120-140 (Fig. B).
Its maximum density is found in units 1 (Lower to Middle
Miocene) and 2 (Upper Miocene to Lower Pliocene). The
third unit (Pliocene in age) shows a lower density of lineaments.
The density and orientation of lineaments do not
depend on the lithology of sedimentary units. Some spatial
variations in their orientation can be observed: near the eastern
border of the basin the NW-SE (parallel to the trend
of main structures) set is dominant, whereas in the
northwestern part the NW-SE and WSW-ESE sets coexist
with the main ENE set. In practically all the central part of
the basin, the ENE trending lines are the most representative.
Most lineaments found in the Neogene rocks of the Almazan
Basin correspond to fractures with little of no-off-
N
N= 2343
ClassInterval = 10 degrees
N = 2332
Class Interval= 10 degrees
set. Some of the orientations found (namely NW-SE and
WNW-ESE) could be inherited from Paleogene structures.
The main set of lineaments, ENE, must be neoformed
structures, possibly controlled by the recent stress field.
The latter is characterised by a NE-SW compression and
NW-SE extension. The ENE fractures could be left lateral
shear joints associated to NE-SW compression. The conjugate
set of joints within this system (NNE-SSW) is much
less developed probably due to border conditions, the overall
brittle deformation being NNE-SSW contraction and
WNW-ENE extension.
MATTHEW SOWTER 1, PETER TALLING 1,
PAOLA REICHENBACH 2 & FAUSTO GUZZETTI 2
. The use of digital elevation models in quantitative
topographic analyses within orogenic mountain belts
1 Department of Geology, Bristol University, Wills Memorial Building,
Queens Road, Bristol BS8 1R], U.K.
2 Cnr-Irpi, via Madonna Alta, 126, 06128 Perugia, Italy
Long-term theories and models of macro-scale geomorphological
processes within orogenic mountain belts
require information regarding the spatial distribution of
different erosional processes. Such data must be both statistically
reliable and available on the broad spatial scales
being examined by the models. Digital elevation models
(Derris) offer the potential to satisfy both these criteria and
have broad implications for modeling geomorphological
change. The Italian Dem covers the entire state and was assembled
by a joint Cnr/Usgs project using data from the
Mean Heights Archive. It has a ground resolution of 230
m, comparing well with other national Dems; for example,
the US national Dem, which has a ground resolution of
805 m. This presentation develops the work of Guzzetti
and Reichenbach 1, and illustrates the potential uses of
such a Dem in the quantitative analysis of mountain belt
topography.
The Apennine mountains in Italy form part of a mountain
chain running from the Po Plain through to Sicily. They
represent an orogenic mountain belt whose morphology is
affected by local tectonic and lithologic patterns. The region
is tectonically active, with numerous thrust sheets and
transverse faults, whilst dominant lithologies are marine sediments.
Even at a national scale, the Italian Dem shows
abrupt changes in morphology throughout the Apennines,
which, upon initial inspection would appear to be related
to lithological variations. At a local scale, the northern
Apennines around Bologna demonstrate a noticeable variation
in topographic form from rounded hillslopes of low
relief to sharply crested linear ridges, even on relatively
small spatial scales of a few kilometres. It is suggested that
such linear crests represent the result of debris flow erosion,
whilst rounded topographic forms are generated by
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