| The Tremiti Archipelago (Southern Adriatic Sea), also called Insulae
Diomedae from the name of the Greek hero who first landed there, is an area
of high landscape and historical value. It is severely affected by
significant geomorphologic processes dominated by mass movements along the
coast that constitute the most important and unpredictable natural hazard
for the population and cultural heritage. Coastal erosion is favoured by the
peculiar geological and structural setting, seismic activity, weathering,
development of karst processes, and wave action.
The present paper reports on descriptive and qualitative evaluation of the
factors controlling landslides and coastline changes based on medium-term in
situ observation, detailed surface surveys at selected locations since 1995,
and historic and bibliographic data.
The Tremiti Archipelago is part of an active seismic area characterised by a
shear zone separating two segments of the Adriatic microplate that have
shown different behaviour and roll back rates in the subduction underneath
the Apennines since middle Pleistocene.
Although coastal morphology can be basically considered to be the result of
wave action, the continual action of subaerial processes contributes
effectively to the mechanism of shoreline degradation. Weathering mainly
affects the marly calcisiltites and calcilutites of the Cretaccio Fm. and
the friable and low cemented calcarenites and biomicrites of the San Nicola
Fm. The cliffs are characterised by different types of failure such as
lateral spreads, secondary topples, rock falls and slides. At the Isle of
San Nicola, landslides are controlled by the contrast in competence, shear
strength and stiffness between the Pliocene re-crystallised dolomitic
calcarenites and calcisiltites and the Miocene marly calcilutites and
calcisiltites. At the Isles of San Domino and Caprara rock falls are
attributed to the undercutting of waves at the base of the cliffs. |