ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

GIACOMO D'AMATO AVANZI
Landslides triggered by the intense rainstorm of 1996
June 19 in southern Apuan Alps (Tuscany, Italy)
Dipartimento di Scienze della Terra, Universita di Pisa,
via S. Maria 53, 56126 Pisa, Italy
The Apuan Alps are a mountain range in Northern Tuscany;
they are mainly formed by metamorphic rocks and
attain the height of ca. 2,000 m above sea level. The chain
imposingly rises on the coastal plain of Versilia, along the
Ligurian-Tirrenian Sea; it is characterized by very steep
slopes and deeply cut valleys. This particular geographic
location very close to the sea, together with the altitude of
the chain, produces the forced lifting of humid air masses
of Atlantic or Mediterranean origin, so favouring their rapid
cooling. Consequently, in the Apuan Alps high levels
of rainfall are recorded, exceeding in some zones 4,000
mm per year; intense rainstorms are frequent, particularly
in spring and summer and cause many landslides.
On 1996 June 19 a very heavy rainfall occurred in southern
Apuan Alps, in the territory that is astride the watershed
between Serchio River and Versilia River catchment basins;
in a recording gauge in this area, a rainfall of 158 mm
in 1 hr was measured during the rainstorm; the recorded
total rainfall was 478 mm in 13 hr. The area involved in
this rainfall was rather small: the 400 mm cumulative rainfall
isohyet was 30 km 2
wide, the 150 mm isohyet was less
then 300 km 2 wide.
The heavy rainfall triggered hundreds and hundreds landslides;
in the mountains, in the maximum rainfall area, ancient
villages, such as Cardoso and Fornovolasco, had
many houses levelled, partly buried or heavily damaged by
debris flows, hyper-concentrated flow and flood. The high
runoff caused severe damages in the mountain .areas along
the streams; in the Versilia plain, the collapse of a river embankment
produced the flooding of ca. 8 km'. Owing to
the catastrophic events there were 14 fatalities.
As to landslides, frequently they were rather shallow, with
a prevailing thickness of some metres (1.5-2 m, with a
maximum of 5-6 rn); the involved material was mostly colluvium,
talus and sometimes weathered portions of densely
fractured rock masses (shales and slates). The rapid infiltration
of rainfall, causing soil saturation and a rise in porewater
pressure is probably the mechanism by which most
shallow landslides were generated. Translational slide was
the most frequent type of movement; the failure surface
usually developed at the contact between the regolith cover
and the bedrock. Sometimes, the failure surface developed
inside the cover or in a dormant landslide, often
with a rotational mode of sliding.
Taking the Cardoso area (one of the more stretched) as an
example, landslides mostly involved talus and colluvium
slopes, accumulated on steep slopes and 1.5-2.5 m thick.
Many typical failure sites were first-order basins and hollows
filled by colluvium, often close to watershed heads;
this geometry favoured the accumulation of colluvium and
the convergence of groundwater flow. In many landslide
sites, the bedrock showed a significant discontinuity (bedding,
schistosity) dipping downslope, so forming a regular
or a stepped 30°-40° inclined plane. Therefore, morpholo-
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gical parameters were very important in landslide development,
often regardless to bedrock type; the involved areas
were mostly covered by woods of big chestnut-trees.
Because of the slope steepness, many debris slides attained
high velocities (at least some m/sec) and then turned into
debris flows or debris avalanches; the movements were often
canalized and characterized by low depth to length ratios
and high length to breadth ratios. Many debris flows
produced ground erosion, while others moved without
causing erosion; likely debris flow waves were produced by
breaching of temporary dam or obstruction in channels.
In addition, a lot of prevailing small landslides involved
roads; they were often caused by high runoff erosion and
led to many road interruptions; thus, several villages had
been isolated. But probably debris-flows, and landslides
from which they generated, were responsible for the greatest
direct or indirect damages, either in the villages or
along the streams.
In conclusion, we regard it significant to remark the role of
landslides in increasing the damage of runoff; in fact, they
abnormally overloaded rivers of fine and coarse sediments
and thousands and thousands of trees. The effects were a.
0.: the rising of riverbed elevations (up to 4-5 m in Cardoso
and Fornovolasco areas), so reducing the supportable
discharge of streams and favouring their flooding; the obstruction
of bridge spans, so determining local floods; the
temporary damming of channels, on collapse of which
flood waves occurred; the increase in destructive capability
of streams, because of sediments and trunks of trees.
MAURIZIO D'OREFICE ', MASSIMO PECCI 2,
CLAUDIO SMIRAGLIA 3 & RENATO VENTURA 1
Monitoring of the Calderone Glacier
(Gran Sasso d'Italia) with Gis technologies
1 Servizio Geologico Nazionale, via Curtatone 3,00185 Roma, Italy
2 Ispesl, Dipartimento Insediamenti Produttivi ed Interazioni
con l'Ambiente, via Urbana 167, 00184 Roma, Italy
3 Dipartimento di Scienze della Terra, Universita di Milano,
via Mangiagalli 34, 20133 Milano, Italy
The study of the variations of the Calderone Glacieris particular
and different from the other glaciers; infact the apparatus
is confined into a deep mountain valley, with steep
walls, and does not show movements along the borders
and the front. So every year, during summer season, it is
possible to measure the thickness of the snow deposed during
the cold season and to evaluate the partial or total
melting, and, in this case, the ice ablation in terms of lost
equivalent in water (D'Orefice & alii, 1996).
Furthemore during the nineties a set of multidisciplinary
researches started to evaluate the role of the Glacier, like
an indicator of the effects of human activities and finally of
regional and global change. These studies included till now
(D'Orefice & alii, in press) and will perform in next years
the measure of ice thickness with geophisical methods
(georadar and geoelectric), the collection of meteorologic
parameters, rains, snow and temperature (Di Filippo &
alii, 1996), the realization of an inventory of available ima-