ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

ANDREW J.e. COLLISON
Simulating the development of preferential flow paths
and gully head collapse using plastic
deformation-hydrology-stability modelling
Department of Geography, King's College London,
Strand, London WC2R 2LS, UK
Much research has highlighted the importance of preferential
flow processes in the development of gullies by headcollapses.
In addition to piping, recent studies have shown
how preferential flow can be caused by water accumulation
in tension tracks. This paper investigates marl gullies
in South East Spain using a combined hydrology-slope St3.""
bility model to demonstrate how Water flow in tension
cracks can trigger head-collapse, and a finite element
deformation model to show how such cracks can develop
in new gully heads by the processes of plastic deformation.
The results suggest that slope undercutting leads the marl
to deform plastically, introducing tension cracks. These are
then exploited as preferential flow paths by overland flow
and throughflow, resulting in the development of positive
pressures at the gully head. These reduce gully head stability
by two processes. Firstly, loss off suction at the gully
head can initiate failure by slumping or toppling. Secondly,
throughflow velocities are raised by an order of magnitude,
favouring the development of suffosion and piping. This
composite model pulls together many hitherto neglected
processes in gully head development and provides an alternative
mechanism to the conventional view of head retreat
by runoff and erosion.
ANDREW J.C. COLLISON\ MARTIN DEHN 2
,
STEVEN.. _.D. WADE 1 & JAMES GRIFFITHS 1
Managing climate change impacts on landsliding .. using
a combined hydrology-stability model to assess
the relative sensitivity of a landslide to climatic versus
landuse change in South East England
1 Department of Geography,
King's College London, Strand, London WC2R 2LS, UK
2 Geographische Institute der Universitat Bonn,
Meckenheimer AIle 166, D-53115 Bonn, Germany
Much recent research has focused on the sensmvity of
landslides to changes in climate associated with global warming.
Climate change predictions for the SE of England
suggest that whilst mean rainfall will persist at current levels,
the distribution will be more uneven than at present,
resulting in more landslide activity. However, these climatic
changes have to be considered in the context of widespread
changes in European landuse associated with set-
aside and re-afforestation. This paper uses a combined hydrology
and stability model to evaluate the relative significanee
of climate change predicted from downscaled Gcm
outputs, compared with changes in hydrological regime associated
with landuse shifts for a landslide complex in SE
England. The results suggest that whilst climate change has
the potential to increase landslide activity, this trend is relatively
insignificant when compared with changes in available
moisture due to vegetation cover conversion and agricultural
drainage. The results highlight the scope for managing
landslides by changing landuse, and offer a potential
methodology for assessing alternative landslide management
strategies.
MAURO COLTORTI
Superimposition, river captures and the Plio-Pleistocene
evolution of the Umbria-Marche area (Central Italy)
Dipartimento di Scienze della Terra, via delle Cerchia 3, Siena, Italy
A «planation surface» preserved on the _Apennine ridge
constitutes the starting point for the evolution of the drainage
network in Central Italy. Its modelling has been associated
to the subaereal erosion which occurred after the
Messinian and possibly until the Lower Pliocene transgression.
In the Middle Pliocene, and possibly until Upper
Pliocene-Lower Pleistocene, a downwarping movement affected
the Tiber as well as the Periadriatic areas which became
basins while upwarping affected the Umbria-Marche
and the Amelia Ridges. The Umbria-Marche Ridge was delimitated,
to the east, by the Sibillini-Urbino thrust front
and, to the west, by a flexure located in correspondence to
the actual graben of the East Tiber valley. Many wide valleys
were formed after the emersion and followed E-W Jurassic
fractures which were locally reactivated during the
thrusting. There were also Apennine valleys originated
from the selective erosion of the softer Oligo-Miocene terrains
which separate a thrust sheet from another. Until the
Lower Pleistocene, a low energy landscape evolved with
large valleys which were separated by hills with many planated
remnants still preserved on their top and a not very
well recognizeable watershed. The eastern side of the depressions
were fed by alluvial fan and fan deltas. In fact,
geomorphic evidence testifies that the main thrust front
(i.e, Sibillini, Martani, etc) were locally reactivated by reverse
faults. Both basins sunk well below sea level. The Peri-Adriatic
basin was filled with marine deposits, while the
Tiber Basin, separated from the sea by the Amelia Mountains,
underwent fluvial, fluvio-Iacustrine and alluvial fan
sedimentation.
At the end of the Lower Pleistocene the uplifting became
more generalized and affected the whole of Central Italy,
although higher values were concentrated along the chain
axe. The down cutting rates increased and were locally
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