ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

A «typical» deposit was chosen, and two sections were
taken into account: a frontal section and a longitudinal one
(figure). They showed an alternance of grain-supported
and matrix-supported layers ..The sedimentological analysis
of each level revealed that these deposits can be interpreted
as eboulis ordonne (according to the classical French
terminology). Each layer, anyway, shows its own sedimentological
peculiarities, either concerning the grain size, or
their orientation and dip, their sorting within the level,
their relative matrix abundance, the degree of cementation,
the nature of its limits. It is impossible, therefore, to
account for a true cyclical nature of the layers.
According to the facies of each level, in comparison with
similar active deposits described in the scientific literature,
an assumption is made about the processes responsable for
the genesis of these deposits: they are hypothized to be
congeliturbation phenomena, associated with rill episodes
and grain flows. The deposits concerned are therefore
likely to have formed in a typical periglacial environment,
near the terminal part of a glacier snout, while this was retreating.
Associated phenomena must have been an increase
of rainfall, quick melting and widespread erosion.
These eboulisordonne are located both above and below at
least two morainic frontal ridges, dated to the Wiirm and
to the Lateglacial; so their genesis was not synchronous,
but formation stages of stratified slope deposits took place
at different times, in different sections of the valley.
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ISSAAK PARCHARIDIS 1, ANDREAS PAVLOPOULOS 2
& MAURIZIO POSCOLIERI 3
Contribution of geomorphometric analysis to a
comparative volcano-tectonic study of Vulcano and
Santorini islands: clues for geologic risk areas
1 Earthquake Planning and Protection Organization,
. 32 Xanthou str., 15451 N. Psychicon, Athens, Greece
2 Laboratory of Mineralogy-Geology, Agricultural University of Athens,
Iera Odos 75, GR- 11855 Athens, Greece
3Istituto di Astrofisica Spaziale del C.N.R., p.p. box 67,
via E. Fermi 21,00044 Frascati (Roma), Italy
In the southern Aegean sea there is a well known volcanic
island complex represented by the Santorini (Thera), Therassia,
Aspro (Aspronissi), Nea Kameni and Palea Kameni
islands (fig. 1). The last two are the actual active volcanic
centers; the general form of the islands and the land distribution
is due to the outstanding Minoan eruption (ca 1500
B.C.) which caused the formation of a caldera and the sea
invasion. The Minoan eruption was characterized by huge
volumes of pumice which covered the existing island. Several
times, later, the volcano erupted again forming the
Palea and Nea Kameni islands. The slopes of the island facing
the caldera are very steep, almost vertical, reaching an
elevation of about 200-300 m a.s 1. Toward the outer periphery
the slopes are, in general, much gentler. The highest
point (566 m a.s.l.) of the island is found in the south east
part of Thera and corresponds to a dome made up of
crystalline limestones (Profitis Ilias) that represent, together
with schists and phyllites, the more ancient island,
before the manifestation of volcanism, whose beginning
has been placed in the Upper Pliocene. The continuing
volcanic activity up to nowadays (last eruption in 1950)
and the related seismic activity exhibit a high risk for the
human settlements and the unstable parts of the caldera
walls.
North of Sicily, in the southern Tyrrhenian Sea, there is
the. volcanic arc of the Aeolian Islands, whose the
southernmost is Vulcano, constituted by many overlapping
volcanic structures (fig. 2). The older one is a stratovolcano,
making all the southern side of the island and partially
facing Sicily; its collapse formed II Piano Caldera.
Northwest of this apparatum, there is a more recent structure
constituted by the Lentia complex, whose collapse
produced again a volcanic depression, inside which La
Fossa cone later grew. Four volcanic cycles have built up
this cone, whose last and huge eruption (only explosive)
occurred at the end of the 19th century at the summit of
La Fossa, occupied at center by the so called Gran Cratere.
The youngest and northernmost center in the island is represented
by Vulcanello, facing the island of Lipari: the
first eruption dates back to the II century B.C., the last to
the XVI century. Vulcano exhibits a very high volcanic risk,
especially in the region corresponding to La Fossa cone,
because of the predominant explosive characteristics of
the eruptions and the presence of human settlements. A
major hazard problem concerns slope instability, strictly
related to and sometimes triggered by the volcanic (nowadays
mostly fumarolic) activity.
A comparison between the two described volcanic scenarios
has been performed by carrying out a quantitative
study of the geomorphological settings of Vulcano and
Santorini. The analysis takes into account as input data sets
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