ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

cal hazard. The geomorphology of the area before and after
urbanization has been established by a comparison of
maps on scales of 1:25.000,1:10.000 and 1:5.000 and of aerial
photographs on a scale of 1:18.000 and 1:10.000.
Gibellina was rebuilt on a low-lying area composed of clay
marl lithologies (Upper Miocene) cut across by a watershed
collecting the waters of a catch basin, which after the
urbanization work was diverted and canalized. The result
is that after critical meteorological events (the most serious
case was in November 1992) the town centre is flooded
and buildings are damaged.
The new sites of Poggioreale and Salaparuta stand on pelitic-arenaceous
terrains (Middle Upper Pliocene) which
even before the urbanization process were subject to widespread
quiescent landslide phenomena of various type (slips,
debris flows) and extent. Many buildings now present
evident lesions due to the reactivation of some landslides.
This situation has negatively affected the physical environment
(altered equilibrium of waterways and slopes) as a result
of acts of territorial planning not prepared for by appropriate
geological and geomorphological studies.
This study identifies the factors of geomorphological instability
and suggests methodologies for interventions in areas
at risk, in the context of a more rational planning of the
territory.
DAVID R. MONTGOMERY
Erosional and tectonic controls on the elevation of
mountain peaks: Olympic Mountains, Washington, USA
Department of Geological Sciences, University of Washington, Seattle,
WA 98195, USA
Isostatic adjustment to valley deepening and increased local
relief can result in the uplift of mountain peaks. A
method for examining the influence of relief development
on the elevation of mountain peaks from topographic profiles
(Montgomery, 1994) was extended to the three-dimensional
case of an entire mountain range in the Olympic
mountains, Washington. The Olympic mountains present
an opportunity to study erosional and tectonic controls on
the elevation of mountain peaks: subduction-related tectonic
convergence drives asymetric uplift of the range and
Quaternary glaciations scoured deep valleys into the heart
of the range. The amount of material eroded from below
mountain peaks was contrained by constructing a 30 m
grid size digital elevation model (Dem) of the range and
then fitting a surface to the collection of highest elevation
points within a search radius that varied from 1 km to 8
km. The volume of material between the present land surface
defined by the 30 m Dem and the surface interpolated
between mountain peaks was averaged over 100 km 2 (10
km by 10 km) grid cells. Maps of the mean elevation,
maximum elevation, present relief, and the equivalent
thickness of the volume of eroded material reveal several
intriguing patterns that allow separation of erosional and
tectonic influences on the elevation of mountain peaks in
the Olympics. Areas of highest present elevation separate
into two primary areas: one centered on Mt. Olympus in
the core of the range and the other to at the eastern end of
the range. The area with the greatest volume of eroded material
centers around Mt, Olympus, whereas the highest
mean elevations concentrate in the eastern end of the range.
Hence, it appears that the location of the highest peak
in the range is controlled by local erosional unloading due
to scour of deep valleys by Quaternary glaciation, whereas
the general area of high elevations at the eastern end of the
range arises from tectonic controls. Plots of the volume of
eroded material versus elevation indicate erosion is not a
simple function of elevation, as the greatest apparent removal
of material occurs at intermediate elevations. This
approach holds the promise of addressing the relative importance
of isostatically compensated valley deepening and
other mechanisms contributing to the elevation of mountain
peaks.
DEREK MOTTERSHEAD 1 & KENNETH PYE 2
Experimental weathering of a clay-rich sandstone
by saline solutions
1Department of Geography, Edge Hill University College,
St Helens Road, Ormskirk, L39 4QP UK.
2 Postgraduate Institute for Sedimentology, University of Reading,
Reading, Berkshire, RG6 2AB UK.
A clay-rich sandstone of Carboniferous age, Forest of
Dean stone, has been shown to weather rapidly in a coastal
saline environment (Mottershead 1994, Pye and Mottershead
1996). The present study investigates in the laboratory
the influence on sample cubes of this rock of various
saline solutions under controlled conditions over periods
of 100 and 200 days.
X-ray diffraction, backscattered scanning electron microscopy,
and microprobe analysis were used to characterise
the rock cubes before and after the experimental runs. The
sandstone consists largely of quartz, feldspar, mica, illite,
chlorite and kaolinite, with trace amounts of iron oxides,
carbonates and heavy minerals. Clay minerals and micas
comprise 10-15 % of the rock, representing both detrital
matrix material and authigenic cement. The fresh rock has
a relatively high compressive strength, of the order of
85MNm- 2 •
Solutions of NaCI, MgS04, MgCb, and CaS04 at various
concentrations were employed, with artificial seawater as a
comparison and deionised water as a control. The mass
and linear dimensions of the samples were measured before
immersion in the saline fluids, and afterwards in the wet
and subsequently oven-dried condition.
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