ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

f) deposition of recent and present-day alluvial sediments
(Holocene).
Tectonic activity, producing E-W and NW-SE trending
faults, affected the area since half graben formation up to
present times.
This sequence of events is also recorded in other depression
of the area and may be considered representative of
the Middle Pliocene-Quaternary evolution of Central
Apennines.
SIRIO CICCACCI 3, LINA DAVOLI ', MAURIZIO DEL MONTE ',
DONATELLA DE RITA 2 & PAOLA FREDI l
The Roccamonfina Volcano:
relations between morphology and tectonics
1 Dipartimento di Scienze della Terra, Universita La Sapienza,
p.le A. Moro 5,00185 Roma, Italy
2 Dipartimento di Scienze della Terra, III Universita,
via Ostiense 169, 00154 Roma, Italy
3 Dipartimento di Geologia e Geofisica, via Re David, 70124 Bari, Italy
This work is part of a wider research concerning the Quaternary
volcanism of Central Italy which aims at determining
the relations among the structural arrangement, the
volcanic history and the present landforms.
The Roccamonfina volcanic district is characterized by the
existence of a central edifice; it belongs to the «Provincia
Romana», a K-alkaline volcanic province that has been active
since 630 ka and up 50 ka. The volcanic edifice is located
where two evident, NW-SE and NE-SW trending fault
systems intersect. The volcanism of the Roccamonfina district
showed three main epochs. The first epoch (630-400
ka) was characterized by both effusive and explosive activity
which gave rise to a strato-volcano and ended when
the volcano summit collapsed and a wide depression originated.
The second epoch activity (385-250 ka) concentrated
on the volcano eastern slope, along NE-SW trending
lineaments. The last epoch activity (250-50 ka) produced
intracalderic lava domes and volcanic centres aligned along
N-S trending lineaments.
Geomorphological analysis has been carried out by using
complementary methods; the aim was to evidence all the
possible controls exerted by tectonic phenomena - and by
the recent ones in particular - on the morphological evolution
of the study area. A precise aero-photo interpretation
has been executed , followed by systematic controls on
field and a geomorphological map of the study area has
been produced. Successively, among the morphological
features surveyed, those identifyable as indicators of tectonics
have been evidenced and all their significant alignments
have been interpreted as faults, probable faults and
fractures; in this way the map of morphological evidence
for tectonics has been drawn.
118
This analysis was supported by morphometric studies concerning
both the hydrographic network and the relief
trend of the investigated area. In particular the areal variations
of the parametres amplitude of relief (Ar) and drainage
density (D) have been examined, since they proved to
be good indicators of lowered or uplifted areas. Of remarkable
interest has resulted the analysis of the stream
channel azimuthal distributions, subdivided into rectilinear
segments by a semiautomatic digitizing process. The
results have been evidenced by means of rose-diagrams,
the main peaks of which show the preferential orientations
, or «domains» of drainage networks. This analysis has
been performed for each of the chosen zones, considering
the whole networks and the channel of each stream order,
since it is likely that streams of different order are controlled
by tectonics in different ways and times.
The analysis of morphological evidences showed the existence
of a rather marked tectonics which controlled the
morphological evolution of the studied area. Four main
tectonic alignments have been evidenced through this kind
of analysis, their directions being respectively NW-SE,
NE-SW, N-S and ENE-WSW. In particular, the first tectonic
alignment is of regional importance and is clearly observable
also outside the studied area; here it borders the
volcanic complex on the eastern side. Of great importance
is also the N -S trending tectonic direction; since it intersects
the main volcanic depression, its activity is likely to
have controlled the morphological evolution of the area in
very recent times.
The analysis of amplitude of relief (Ar) and drainage density
(D), both of them calculated for unit of area, afforded
useful information about the role of tectonics on the present
morphological arrangement of the studied area. The
areal variation of these parametres allowed the identification
of different zones which can be considered downthrown
as respect to the adjacent ones.
The statistical analysis of the preferential orientations of
stream channels confirmed the above expressed considerations.
Although the existence of the volcanic relief favours
the development of a centrifugal drainage pattern, many
anomalies exist within it, which suggests the existence of a
marked structural control. In conclusion, geomorphological
analysis carried out evidenced that the volcanic activity
and the morphological evolution of the studied area were
strongly controlled by tectonic activity also in very recent
times. More in details it has been evidenced that the tectonic
directions NW-SE, NE-SW and ENE-WSW were responsible
for the general arrangement of the area which
can be subdivided in different sectors differentially uplifted
and downthrown starting from Upper Pliocene. Moreover
the surface effects of the N -S trending tectonic direction
are discernable; this direction crosses the volcanic
products and conditioned the emplacement of lower order
stream channels, thus testifying the important role it had
not only in the recent volcanological history but also in the
very recent geomorphological evolution of the Roccamonfina
area.