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Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
141
DOI: 10.4408/IJEGE.2013-06.B-11
GRAVITY-DRIVEN DEEP-REACHING DEFORMATIONS AND
LARGE-SCALE LANDSLIDES IN RECENTLY UPLIFTED MOUNTAIN AREAS:
THE CASE-STUDY OF MT. CUCCO AND BELPIANO
(LIGURIAN APENNINE, ITALY)
F
rancesco
FACCINI
(*)
, a
ndrea
ROBBIANO
(**)
, e
manuele
RASO
(**)
& a
nna
ROCCATI
(**)
(*)
University of Genova - DISTAV - Corso Europa, 26 - 16132 Genova, Italy (faccini@unige.it)
(**)
Engineering Geologist, Italy
the sliding mass potentially affected by DSGSD and
taking in consideration the erosional activity of Sturla
river at the bottom of the slope and the actual climate
changes it's reasonable to suppose that a reactivation,
even partial, of DSGSD could create a landslide lake
along the Sturla stream and a consequent high risk for
several thousand people living downstream in the vil-
lages of Borzonasca, Mezzanego and Carasco.
K
ey
words
: Deep Seated Gravitational Slope Deformation,
landslide, Northern Apennines
INTRODUCTION
In Ligurian Apennines, the Deep Seated Gravi-
tational Slope Deformations (DSGSD) represent an
important geomorphological landscape feature, both
along the coast and in the hill-mountain environment
(Z
ischinky
, 1966; 1969; n
emcok
, 1972; s
avage
&
v
arnes
, 1987; c
rosta
, 1996; c
rosta
& Z
anchi
, 2000).
Only recently they have been identified and accurately
studied scientifically, unfortunately for the most part in
a manner not suitable to their extension and complexity.
The attention towards these phenomena is linked
to the important involvements brought by DSGSD in
activities such town and land planning and environ-
mental protection.
The acronym DSGSD refers to deep slope defor-
mations associated with high energy-relief; generally
the deformation value is small compared to the exten-
sion of the area affected by this phenomenon (d
ramis
ABSTRACT
This work concerns with a DSGSD located in upper
Sturla Valley (Northern Apennines, Italy), in the Munic-
ipality of Borzonasca, in an recently uplifted mountain
area where the historic Belpiano hamlet was settled.
The investigation of DSGSD was carried out
through field survey, historic maps comparison, drill-
ing and monitoring activities; seismic surveys were
carried out in order to define the depth of the bedrock
not involved in the DSGSD.
The DSGSD origin is related to the slope par-
ticular geological structure with hard, fractured sand-
stones overlaying weak shales and characterized by
a consequent high groundwater circulation supported
by large amounts of rainfall, typical of this geograph-
ic area. Other DSGSDs have been studied and regis-
tered in this particular geological contest of Northern
Apennines, actually in the Gottero Unit areas belong-
ing to the upper Sturla Valley.
Clear morphotectonic and geomorphological ele-
ments of activity have been detected, in addition to
rock blocks detached by the bedrock and sliding mass-
es related to active landslides. The most significant
phenomenon is the landslide which involved the an-
cient parish church of Belpiano during XVII century;
another event occurred in 1982 when a heavy rainfall
greater than 600 mm over 5 days caused a hydrogeo-
logical disaster involving the whole Sturla Valley.
Because of the large amount of rock and debris
(ranging 320-480 millions of cubic meters) forming
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F. FACCINI, A. ROBBIANO, E. RASO & A.ROCCATI
142
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
this DSGSD, to pick out the deformation dynamics and
to evaluate the actual geomorphological hazard.
Other large and complex geomorphological ele-
ments have been identified in the Sturla Valley (B
ran
-
dolini
et alii, 1991; d
e
s
teFanis
et alii, 2001; 2002)
but not related to other DSGSD. The analyzed por-
tion of slope has been recently included among the
regional areas under investigation of the IFFI project
& s
orriso
v
alvo
, 1994; s
orriso
v
alvo
, 1995).
The most typical features of a DSGSD are the
high number of tectonic lineaments and morpho-
logical elements produced by structural causes, the
extension of the area afflicted which is often cor-
responding to the slope area, the small value of
present displacements (in the order of few cm/year),
the presence of significant landslides inside the de-
formed area (a
gliardi
et alii, 2001; 2009).
In the Liguria region, northwestern Italy, is rela-
tively common to find different lithologies belonging to
one of the two most important Italian mountain chains
(Alps and Apennines) close to each other, in geome-
chanical and hydrological terms. The rock masses are
often highly deformed, fractured and altered. Further-
more Ligurian Apennines are characterized by higher
energy-relief, the Plio-Pleistocene tectonic lineations
are particularly active, the seismic activity is signifi-
cant, and important climate variations have been pro-
tracted all along the Quaternary (F
accini
et alii, 2009a).
This paper is concerned with a DSGSD involving
the entire system ridge, slope and valley floor, sited
on the right side of the upper Sturla Valley (Ligurian
Apennines) where an extensive and accurate site in-
vestigation was carried out.
The mountain side on which is located the village
of Belpiano, hamlet of the Borzonasca Municipality, is
historically affected by slope instability phenomena:
through a long archival research it has been possible to
identify some active landslides which caused the loss of
several human lives starting from XVII century. Hence,
our goal is to increase the scientific knowledge about
Fig. 1 - Location map of the studied area, tectonic and
neotectonic sketch maps (modified from APAT,
2005 and F
anucci
et alii, 1980). Legend of tec-
tonic sketch map (A): Internal Ligurides: 1.
Gottero Tectonic Unit, Loco Subunit (a) and Ram-
aceto Subunit (b); External Ligurides: 2. Ottone
Tectonic Unit; 3. Mt. Aiona Element. Legend of
neotectonic sketch map (B): 1. Area affected by
relative uplift; 2. Area affected by absolute uplift;
3. Fault
Fig. 2 - Geological map (modified from APAT, 2005). Legend:
1. Deposits mainly due to gravity; 2. Mainly colluvial
deposits; 3. Alluvial deposits; 4. Argilliti di Giaiette
(shales); 5. Arenarie di Mt. Gottero (sandstones); 6.
Scisti Zonati (silstones and shales); 7. Olistostromi
del Passo della Forcella (olistostromes); 8. Ardesie di
Mt. Verzi (slates); 9. Argille a Palombini (shales with
limestone interlayers); 10. Complesso di Casanova
(a. Ophiolitic sandstones; b. Mono and polygenetic
breccia with clayey matrix; c. Polygenetic breccia
with sandy matrix); 11. Basaltic olistoliths; 12. Ul-
tramafic olistoliths; 13. Cherts; 14. Normal beds; 15.
Overturned beds; 16. Beds with uncertain polarity;
17. Vertical beds with uncertain polarity; 18. Hori-
zontal beds; 19. Foliation of axial plane, 2nd phase;
20. Stratigraphic contact; 21. Faults, certain or as-
sumed; 22. Main tectonic contact; 23. Secondary tec-
tonic contact; 24. Trace of anticline axial plane; 25.
Trace of syncline axial plane; 26. Axis of meso-fold,
1st phase; 27. Axis of meso-fold, 2
nd
phase
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GRAVITY-DRIVEN DEEP-REACHING DEFORMATIONS AND LARGE-SCALE LANDSLIDES IN RECENTLY UPLIFTED MOUNTAIN ARE-
AS: THE CASE-STUDY OF MT. CUCCO AND BELPIANO (LIGURIAN APENNINE, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
143
(maximum of annual rainfall level in the whole area
of Liguria region). The average monthly rainfall dis-
tribution shows a maximum in November (250 mm)
and a minimum in July (60 mm). Heavy concentrated
rainfalls are often observed during the Fall season,
when they can reach values as much high as half of
the annual total only in a few days.
The investigated area belongs to the tectonic do-
main of the Internal Liguride Units (APAT, 2005) and
in particular to the Gottero Unit (Fig. 1): the upper and
medium portion of the slope belongs to the Ramaceto
Subunit, while the bottom of the slope belongs to the
Loco Subunit. The tectonic contact between Internal
Liguride Units and the Ottone Unit (belonging to Ex-
ternal Liguride Units, whose overturned formations
outcrop at the orographic left of the Sturla river) is
located along the valley floor (c
asnedi
et alii, 1983;
1993). All the area is affected by a general uplift
which started in lower Pleistocene, proved by several
linear and areal features (F
anucci
et alii, 1980).
The stratigraphic succession on the orographic
right starting from the bottom to the top is made by
Argille a Palombini, Ardesie di Mt. Verzi, Scisti Zonati
and Arenarie di Monte Gottero, locally overlaid by por-
tions of Argilliti di Giaiette (Fig. 2 and Tab. 1).
The Internal Liguride Units are characterized by
a complex geological structure: during the period be-
tween Upper Paleocene and Lower Eocene these units
were involved in a subduction process associated with
the closure of the Ligurian-Piedmontese oceanic ba-
sin. The tectonic evolution of the internal Ligurian
Units took place through two main deformational
events associated with a compressional overthrusting
which brought to a complex structural character.
The structural evolution can be well recognized in
the Gottero, Bracco-Val Graveglia e Tavarone Units
and therefore can be described in a single way (M
ar
-
roni
, 1991; a
pat
, 2005).
The first deformation event is defined by isoclinal
folds with similar geometry; the hinge zone is gener-
ally thick and rounded, while the limbs appear thin
and boudinaged. These folds are strongly non cilindri-
cal with fold axis strike in a range from N160 to N30.
These isoclinal folds are often associated with a slaty
cleavage foliation which is clearly visible at the hinge
zone while sometime it could be mixed up with the
strata surface along the limbs.
The second deformation event is characterized
(Inventario Fenomeni Franosi in Italia, B
ottero
et
alii, 2004) and in the SCAI project (Studio dei Centri
Abitati Instabili, F
ederici
et alii, 2004); however both
the projects say there is no evidence of activity of the
Belpiano DSGSD, therefore the mass wasting is con-
sidered ancient and relict.
In regard of the geographical location of the ana-
lyzed DSGSD, bordered at the bottom by a significant
river and with several villages downstream (three of
them, Borzonasca, Carasco e Mezzanego add up more
than 7,000 people), not only more information about
the dynamics of this gravitational phenomenon are re-
quired, but above all is necessary to monitor and keep
studying it, remembering what happened during the
catastrophic event of the Vajont landslide in 1963.
GEOGRAPHICAL AND GEOLOGICAL
FRAMEWORKS
The investigated area is located on the orographic
right of the Sturla river (Entella river catchment), up-
stream the village of Borzonasca (Fig. 1); its north
boundary is the alignment between Mt.Cucco and Mt.
Fracucco, while the southern one is the bottom of the
Sturla Valley, covering a total length of 800 meters
and an extension of 4 km
2
.
The main settlement inside the DSGSD area is
Belpiano (485 m a.s.l.); other smaller hamlets are
located at a lower altitude (Frasineto at 343 m a.s.l.;
Casa Mugè at 322 m a.s.l.) and some others at a higher
elevation (Acero at 538 m, Cà dei Grilli at 720 m, Lu-
vega at 781 m a.s.l.).
The climate of the area is defined by the parame-
ters recorded at Tigliolo weather station (293 m a.s.l.)
whose location is very close to the area under inves-
tigation: the prevailing climate is Mediterranean. The
geographic setting and the main slope configuration
of the Sturla Valley create an air mass circulation of
wet and warm winds blowing from the Ligurian Sea.
Due to these conditions, relatively mild tempera-
tures are generally observed, with an average of 13-
14°C, with average annual rainfall of almost 2000 mm
Tab. 1 Description of geologic formations and related
outcrop areas
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F. FACCINI, A. ROBBIANO, E. RASO & A.ROCCATI
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International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
The analysis of aerial photographs (Istituto Ge-
ografico Militare - 1954, scale 1:55,000 and Regione
Liguria - 2006, flight no.73 scale 1:13,000) combined
with geological and geomorphological field survey
carried out at 1:5.000 scale revealed the presence of
several different landforms and tectonic lineaments.
The study included a detailed survey of damage
caused by DSGSD involving man-made structures,
focusing on buildings, communication routes, rein-
forced-cement and dry-stone walls.
Particular attention has been pointed towards the
geomorphological features related to neotectonics, di-
rectly associated with wide instability processes.
In order to represent the general morphological
and deformational pattern, a digital elevation model
(DEM) was obtained through different CAD/GIS
packages (ESRI ArcGIS). A georeferenced contour
map in a vector format obtained from a Lidar survey
with a 1 point/m resolution has been prepared (Fig. 3);
the DEM obtained in such way has been used to pro-
duce a shaded relief map. Morphometric analysis of
the DEM outlined a lower sector with convex profile
and a convex upper part: the slope shows a general saw
tooth shape, whose angle of dip ranges from 26° to 36°
between 950 m and 1050 m, between 800 m and 500 m
and between 450 m and 250 m a.s.l.; the rate is lower
than 11° between 485 m and 492 m and between 840
m and 890 m a.s.l., while at the remaining heights the
slope angle of dip ranges from 11° to 26°.
A specific investigation was carried out through
an accurate bibliographic research in historic archives,
several interviews at the local residents and a com-
puter research to catalog all the landslides which af-
flicted the area during the past centuries (c
onsiglio
n
aZionale
delle
r
icerche
, 1994).
Particularly interesting was the research of historic
maps which gave an important contribute to analyze
the slope dynamics during the last centuries; here are
reported the titles of the works: a) “Pianta delle tre ville
d’Acero, Trigoso e Porcile con distanze, strade, boschi
e corsi d’acqua” made by the Architect Sebastiano Pon-
sello and the painter Stefano Sturla, dated 1645 and pre-
served at the “Archivio di Stato di Genova”; b) “Carta
del territorio compreso tra Genova, Spezia e il confine
col Ducato di Parma”, paper n.63, scale 1:9450, dated
1816-27 and preserved at the cartographic archive of
the “Istituto Geografico Militare Italiano”; c) Boards
in scale 1:25.000 “Borzonasca” property of “Istituto
by folds with parallel geometry, from gentle to tight
interlimb angle, generally asymmetric and of various
shape. The interlimb angle could vary in a range from
a minimum of 30°/40° to a maximum of 100°/110°.
The fold axis strike goes from N140 to N180. This
second deformation event shows wide and extended
reverse limbs associated with overturning of the fig-
ures originated during the first deformational event.
Both in the first and in the second event an axial plane
foliation classified as crenulation cleavage is recog-
nizable. During the second deformational event a nor-
mal, extensional high angle fault system took place
involving the Gottero Unit; strike angle of fault planes
are included in a range between N160 and N20.
Large scale structural figures are visible along the
upper Sturla Valley, where anticline folds belonging
to the first deformation event inside the Ardesie di Mt.
Verzi formation were deformed by gentle anticline
and syncline folds belonging to the second phase.
After the first two deformation events a last geo-
logical phase took place during the Plio-Quaternary:
an extension caused by the normal fault component
of movement along the northern portion of the Apen-
nines and a relative sequence of horst and graben ar-
eas. The analysis of the focal mechanisms related to a
low seismic activity in north western Italy proves that
the extensional Quaternary phase is still in progress.
METHODS
The knowledge of the geological and geomorpho-
logical features is essential to understand the evolu-
tion of a slope affected by DSGSD.
Fig. 3 - Shaded relief map based on the DEM performed
with Lidar survey with a 1 point/m resolution; the
main DSGSD and landslide scarps are indicated
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GRAVITY-DRIVEN DEEP-REACHING DEFORMATIONS AND LARGE-SCALE LANDSLIDES IN RECENTLY UPLIFTED MOUNTAIN ARE-
AS: THE CASE-STUDY OF MT. CUCCO AND BELPIANO (LIGURIAN APENNINE, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
145
field program consisting of 8 boreholes (3 continu-
ous boreholes and 5 nucleus destruction drilling). The
boreholes were carried out in the Belpiano area and
reached 80 meters of depth (Tab. 2).
The boreholes were equipped with geotechnical
and hydrogeological instrumentation: more specifical-
ly, three boreholes were instrumented with inclinom-
eter case and five were instrumented with piezometer
case (Fig. 4).
The monitoring activities were carried out for
more than 3 years (2003-2007).
The field program has been integrated by both seis-
mic refraction and reflection investigation (seismometer
type Abem Terraloc Mark 6 with 24 channels) made
along a 150 meters line and energizing the ground with
some minibangs to the purpose of gaining more informa-
tion about the mechanical condition of the portion of the
bedrock potentially not involved in the DSGSD process.
RESULTS
FIELD SURVEY
A field survey was carried out at the slope por-
tion between Casa Cugno (northern boundary) and
San Rocco (southern boundary) revealing the pres-
ence of several different types of landforms, suggest-
ing a complex evolution of the area during the uplift
Quaternary phase of the Northern Apennines; this is
proved by fluvial deposits found during some excava-
tions 200 m above the present level of Sturla river.
Many other morphological features caused by neo-
tectonics were found, such as a straight evolution of the
ridge over the investigated slope, several depressions in
correspondence with some recent tectonic lineaments
and a large gravitational trench related to a tectonic
cause parallel to the main ridge at 800 m a.s.l. (Fig. 5).
The drainage pattern has a mainly rectangular
shape with many simple and double elbows alternated
Geografico Militare Italiano” 25v series, made in 1904
(first edition) and 1937 (third edition); d) Board in scale
1:25.000 “Borzonasca”by “Regione Liguria” - made
with the contribute of aerial photography in 1992.
Many geomorphological and geological works per-
taining to this area and focused on gravitational land-
forms and processes (p
rovincia
di
g
enova
, 2002) and
other reviews about the landslide insisting on the inves-
tigated zone (d
ramis
et alii, 1985) were deeply analyzed
to improve the general knowledge of the phenomena af-
fecting this portion of Northern Apennines.
Within the project of mitigation of natural hazard
of the slope affected by DSGSD on which is located
the village of Belpiano, Regione Liguria promoted a
Tab. 2 - Drillings and slope monitoring data (I: inclinom-
eter; P: piezometer)
Fig. 5 View of the Mt. Cucco and Belpiano area. The up-
per sector of the DSGSD with the main scarp and
Cà dei Grilli and Lavaggi ridge is shown
Fig. 4 - Drills and geophysical surveys location map with
building damages classification (orange: high; yel-
low: medium; green: low). LEGEND: I. borehole
with inclinometer case; P. borehole with piezometer
case; a. seismic reflection trace; b. preliminary walk
away noise test; c. seismic refraction trace
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F. FACCINI, A. ROBBIANO, E. RASO & A.ROCCATI
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International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
with straight segments; this complex trend suggests a
main tectonic role during the evolution of the pattern.
Furthermore some triangular and trapezoid fig-
ures were found on the right bank of Sturla river, lo-
cated between the valley floor at 250 m a.s.l. and the
Belpiano village.
Debris cover characterizes a wide portion of the
investigated area; these gravitational deposits are de-
fined by different dimensions, genesis and kinematics
while the few rocky outcrops marked in the investi-
gated area are linked to rock blocks.
A relevant active landslide insisting on a flat area
located south of Belpiano is the one starting from the
northern side of Mt. Cucco and extending towards
NE, more than one kilometer long and with a main
flow kinematics (Fig. 6); standing on historic state-
ments dated XVII century, a landslide occurred on this
portion of the slope at the same level of the present
village of Belpiano (Fig. 7), destroying the ancient
parish church whose ruins are still visible. Another
event occurred here in September 1982 when a heavy
rainfall greater than 600 mm over 5 days was indi-
cated as the main cause of a hydrogeological disaster
in the Sturla Valley (F
accini
et alii, 2009b).
Another significant landslide adjacent north to the
previously described one insists on the hamlet of Bel-
piano; this landslide is complex, dormant and smaller
than the active one. Other smaller gravitational events,
Fig. 6 - Geomorphological and morpho-structural map of the studied area. LEGEND: 1. Clayey shales; 2. Sandstone with
thin interlayers of shales; 3. Clayey shales with siltstone layers; 4. Clayey shales with limestone layers; 5. attitude
(a. dipped; b. overturned); 6. normal fault (a. certain; b. assumed or covered); 7. overthrust; 8. edge of scarp (a.
active; b. inactive); 9. reverse slope; 10. edge of degradational scarp; 11. rock defile with rock fall; 12. landslide due
to flow (a. active; b. inactive); 13. complex landslide (a. active; b. inactive); 14. scree slope; 15. trench; 16. closed
depression; 17. river elbow; 18. downcutting stream; 19. abandoned stream; 20. riverbed with lateral erosion; 21.
edge of erosion scarp; 22. widespread outwash; 23. alluvial deposits (sand and gravel); 24. debris flow; 25. colluvial
deposits; 26. archaeological site; 27. main stream barrages; 28. springs
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GRAVITY-DRIVEN DEEP-REACHING DEFORMATIONS AND LARGE-SCALE LANDSLIDES IN RECENTLY UPLIFTED MOUNTAIN ARE-
AS: THE CASE-STUDY OF MT. CUCCO AND BELPIANO (LIGURIAN APENNINE, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
147
the current parish church (built in 1661 by the monks
of Borzone Abbey), cemetery buildings and school
building; the ancient constructions also better show
the damage caused by differential settlement and
destabilizing loads on foundations and bearing walls.
Along the streets surrounding the area some walls and
gabionades are swelling because of hydraulic
pressure, especially next to torrents. Some main-
tenance works have been carried out during the last
ten years to mitigate the water superficial erosion, but
it wasn't enough to oppose the damaging action on
embankments and retaining walls of the big amount
of solid material carried downstream.
In consequence of high energy conditions, plu-
viometric profile and type of landslides the drainage
pattern is deepening; furthermore the river beds of the
streams belonging to the right riverbank of Sturla river
such as T. Belpiano, T. Castellina and Rio Ciattina are
often location of debris flows.
TECTONIC LINEAMENTS
Through an accurate field survey and the analysis
of aerial photos it has been possible to identify more
than three hundred tectonic lineaments related to sev-
eral sets of extensional faults.
Four main sets of tectonic alignments have been
identified: i) WNW-ESE striking, NNE subvertically
dipping normal faults and joints system; ii) N-S and
NNW-SSE oriented subvertical fractures; iii) SW-NE
towards ENE-WSW striking joints and normal faults,
steeply dipping to NW or SE; iv) E-W trending subor-
dinate set of subvertical normal faults.
WNW-ESE and ENE-WSW (SW-NE) trending
fracture systems are the most frequent in the area. This
could suggest a recent reactivation of these structures,
which seem to interrupt the continuity of the N-S
(NNW-SSE) and E-W trending sets. This observations
is in agreement with F
anucci
et alii (1980) about the
neotectonic framework of this part of Ligurian Apen-
nine and with the orientation of the main DSGSD fea-
tures reported in Fig. 6. These fractures strongly influ-
ence the trend of the valleys, such as the NW-SE and
SW-NW general trending of the upper Sturla Valley
and causing in such sector landforms like scarps (upper
slopes of Mt. Fracucco). Trend analysis of photo-in-
terpreted alignments performed by a GIS software en-
hances the influence of the WNW-ESE and ENE-WSW
trending brittle structures on the drainage pattern in the
some of them still in activity, are identified close to the
northern border of the DSGSD and at its bottom.
Several counterslopes give the mountainside a
saw tooth shape with plain areas often delimited by
uphill facing scarps irregularly interposed to steep
rocky slopes alternating with small depressions filled
with cohesive sediments – the village of Belpiano was
settled on one of these deposits.
Degrading scarps and related scree slopes are vis-
ible under the watershed between Mt. Cucco (1051 m)
and Mt. Fracucco (1095 m).
The geomorphological dynamics of the slope
produces several damages on the buildings of Belpi-
ano, especially cracks and ruptures mostly visible in
Fig. 7 - Historical maps of the studied area. - At the top:
map of 1645 (Archivio di Stato di Genova); In
the middle: map of 1816-27 (Archivio Storico
dell’Istituto Geografico Militare Italiano); At the
bottom: map of 1937 (Tavoletta dell’Istituto Ge-
ografico Militare Italiano). The red circle points
out the position of the old church destroyed at the
end of XVII century, while the blue circle points
out the position of the present church
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F. FACCINI, A. ROBBIANO, E. RASO & A.ROCCATI
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International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
that identified two main sequences: the first one con-
sisting of landslide deposits in contact with the second
one identified as the bedrock at a depth of 160-200 m.
Furthermore two vertical discontinuities were identi-
fied: the first one, less visible than the second one in
the test results, apparently doesn't affect the bedrock
dip while the second one displaces the sandstone and
shales beds accentuating their dip values (Fig. 8).
Data coming from inclinometer monitoring carried
out for more than three years show activity signs on the
south-eastern side of the flat area on which the village of
Belpiano is settled: failure surface has been identified at
a depth of 46 m below g.l., while another discontinuity
has been determined at a depth range between 20 m and
25 m. Cumulative displacement at the top of the borehole
indicates a landslide velocity ranging from 4 to 24 mm/
year which is considered a very slow and extremely slow
in the landslide velocity scale (c
ruden
& v
arnes
, 1996).
Standing on test results coming from seismic sur-
veys, more weakness surfaces could be present at deeper
level than the one reached through the drilling project.
Through groundwater monitoring it was found
that the third soft soil level identified through seismic
of refraction survey is an aquifer and that the water
table is above the main slip surface with scarcely or
no correlation with the rainfall data for this area.
DISCUSSION
Field investigations, drilling tests and geophysi-
cal surveys have significantly contributed to describe
in detail an important deep-seated gravitational slope
deformation affecting the entire slope between the
Sturla river and the rectilinear ridge of Mt. Cucco
and Mt. Fracucco.
The slope deformation consists of a large ob-
lique “sagging” along a structurally controlled deep
confined sliding surface and associated with recent
gravitational reactivation of preexisting tectonic
lineaments (Fig. 9).
right side of the upper Sturla Valley and consequently
control the development of the DSGSD and landslides.
DRILLS AND GEOPHYSICAL TESTING
Through the drilling project carried out in the Bel-
piano area it has been possible to evaluate the mini-
mum thickness of soil deposits related to landslide dy-
namics around 80 m (Tab. 2); despite of high values of
depth reached none of the boreholes has encountered
the top of the bedrock. This large amount of sediment
consists of coarse debris made of gravel, pebbles and
cobbles in a silt-sandy matrix (c
anepa
et alii, 2003).
The punctual results from drilling project has
been extended to the whole area through an accurate
geophysical investigation. Seismic of refraction in-
vestigation has been carried out for 150 m and the test
results analysis contributed to make a three sequence
seismic profile: the first identified level has seismic
waves velocity values around 400-500 m/s and it has
a high void ratio; in the second one seismic waves ve-
locity values are included between 900 and 1100 m/s
and it's identified as a soft soil with random boulders;
the third and last one shows higher values of seismic
waves velocity (between 1950 m/s and 2150 m/s) and
its composition is considered similar to the second
level but saturated because under ground-water level.
Seismic of reflection survey provided information
Fig. 8 - Seismic profile: A and B are main reflective sur-
faces (probably the top of the bedrock), C is a
shallow reflective surface (mainly fine grained
soil), D and E are subvertical discontinuities
Fig. 9 - Geological and morphostructural cross section
through a SW-NE trace (see Figg. 4, 6, 8 and Tab. 2)
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GRAVITY-DRIVEN DEEP-REACHING DEFORMATIONS AND LARGE-SCALE LANDSLIDES IN RECENTLY UPLIFTED MOUNTAIN ARE-
AS: THE CASE-STUDY OF MT. CUCCO AND BELPIANO (LIGURIAN APENNINE, ITALY)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
149
(F
anucci
& n
osengo
, 1979).
One of the most important tectonic lineaments
is the NNE-SSW trending Sturla river fault which
caused great mass displacements all along the Stur-
la Valley when the neotectonics earthquakes were
stronger and more frequent than the present ones.
Despite the fact that a general geomorphological
survey has been extended to the whole mountainside
area, a deeper direct and indirect analysis has been
carried out only in the middle and lower portion of
the slope because of the major importance of that
zone in the eyes of environmental risk.
The Belpiano area can be interpreted as a tectonic
gravitational trench characterized by a counterscarp
typical of sackungs (B
isci
et alii, 1996; d
ikau
, 1999),
filled up by fine sediments before and by fluvial depos-
its later because of the droop of the area.
In terms of geomorphological activity, many
landslides of different type and dimension took place
during the last century in this portion of territory
involving several buildings and infrastructures; the
most recent event is dated 1982, when the southwest-
ern portion of the Belpiano hillock was hit by a land-
slide whose sliding mass reached the valley floor.
The preliminary results of the inclinometer
monitoring system clearly indicate that the slope is
subjected to a present state of activity, with a main
slip surface at around 46 m below g.l., although it
is evident that displacement could be active along
deeper highly fractured horizons.
The lack of monitoring of the upper part of the
slope prevents the assessment of activity. However
morphological evidence observed through a field sur-
vey suggests inactive condition of the Cà dei Grilli
and Lavaggi ridge, although low rate displacements
along structural lineaments cannot be excluded.
It is legitimate to point out that wide and deep land-
slides as the one described in this paper have had an
important role also in other ligurian valleys and espe-
cially in some adjacent ones: some DSGSDs belong-
ing to Gottero Unit have been recognized in the lower
Graveglia Valley (B
randolini
et alii, 2007), in the up-
per Aveto Valley (B
randolini
et alii, 2008) and in the
Lavagna Valley (c
apitani
, 2010). These DSGSDs took
place in the same previously described geological and
tectonic contest also found in other mountain chains
(p
anek
& alii, 2009), in which hard lithologies (like
sandstone or marly limestone) are overlying weaker
The DSGSD caused the formation of mainly
WNW-ESE trending trenches, double ridges, depres-
sions, scarps and counterscarps.
The general contour of the mountain side is a
saw tooth shape with upward dipping surfaces alter-
nating with flat areas between almost 850 m a.s.l. and
the valley floor of the Sturla river.
The evolution of the WNW-ESE and ENE-WSW
trending systems caused the progressive bulging and
failure of the lower part of the slope and is still in
progress in the area of the active landslides.
The Cà dei Grilli and Lavaggi ridge has been
displaced downstream with a NE component of mo-
tion; morphological and lithological markers suggest
a downward displacement of 150-200 m in the upper
part of the slope.
Starting from preexisting discontinuities, some
listric faults associated to antithetical minor dip slip
surfaces developed, forming asymmetric trenches.
The age of the DSGSD can be obtained from the
relationship between morphostructural features and
Quaternary landforms deposits (B
randolini
et alii,
2008). Several swampy deposits characterizing the
summit trenches related to other deep slope defor-
mations in the Northern Apennines zone have been
analyzed through radiocarbon dating (B
ranch
, 2004):
these sediments have been dated 11670±70 years BP,
at the end of the Younger Dryas (s
everinghaus
et alii,
1998), therefore is plausible to assert that the deforma-
tion took place before that period.
On the basis of the available data three main fac-
tors are considered important for the understanding
and modeling of the DSGSD evolution: the first one is
a geological factor consisting of brittle layers overlay-
ing ductile lithologies and a permeability difference
between these formations with consequent high pore
pressure values along the deep failure surface; the sec-
ond one is the unloading and decompression of a fold
and thrust belt structure caused by the deepening and
undercutting of the slope mainly produced by river
erosion; the third and last one is the periodic alterna-
tion of glacial and interglacial Quaternary phases.
Is possible indeed to identify the regional uplift
of Ligurian Apennines during Plio-Pleistocene as the
main endogenous reason for the tectonic lineaments
system which contributed to shape the present slope
counters of both the northern and southern mountain
side of Northern Apennines and the actual coastline
background image
F. FACCINI, A. ROBBIANO, E. RASO & A.ROCCATI
150
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
levels (shales). Even in these areas similar geomorpho-
logical and morphotectonic features are pointed out,
like saw tooth shape of the mountainsides with small
depressions filled with lacustrine cohesive sediments.
The geomorphological risk of these other DSGSDs is
comparable to the analyzed DSGSD affecting the ham-
let of Belpiano and, in regard of the population density
belonging to this hillside area, the consequent geomor-
phological hazard must be carefully evaluated in rela-
tion with the DGSGD evolution.
CONCLUSION
This work proposes an integrated multidiscipli-
nary approach: the analysis of the mountainside in the
upper Sturla Valley on which is settled the Belpiano
village from a geological, structural, geomorphologi-
cal and engineering-geological point of view through
detailed field surveys, multi-temporary cartographic
studies made at different times and in situ direct and
indirect test programs has increased the understanding
of a typical DSGSD case in Northern Apennines.
The knowledge of DSGSD in terms of town and
land planning and environmental protection is impor-
tant because of their closeness to several villages and
hamlets: to this end, it must be told that the village of
Belpiano has been recently renovated and consequent-
ly there will be a higher flow of tourism in the area.
Because of the large amount of rocks and sedi-
ments (3-4 hundreds of millions of cubic meters) form-
ing the sliding mass potentially affected by DSGSD and
taking in consideration the erosional activity of Sturla
river at the bottom of the slope and the actual climate
changes it's reasonable to suppose that a reactivation,
even partial, of DSGSD could create a landslide lake
along the Sturla stream and a consequent high risk for
several thousand people living downstream in the vil-
lages of Borzonasca, Mezzanego and Carasco.
Furthermore during the last years due to the par-
ticular morphoclimatic condition of the Gulf of Genoa
many flash floods have hit the central portion of Ligu-
ria (F
accini
et alii, 2012) and this clearly represents
a further destabilizing factor for wide landslide areas
(h
endron
& p
atton
, 1985); for example in 1970 dur-
ing the Genoa flooding event 750 mm of rain water fell
in less than 24 hours while in 1982 in the upper Sturla
Valley 540 mm of rain water fell in almost 24 hours.
A further implementation of geotechnical and
hydrogeological monitoring activities is recom-
mended to obtain more data and information about
the DSGSDs dynamics in different areas and time
periods, especially for the active ones. Data obtained
from Interferometric Synthetic Aperture Radar (In-
SAR) monitoring combined with the installation of
radar targets in the area could also be extremely use-
ful for this purpose.
The investigation of the Mt. Cucco and Belpiano
DSGSD is to be considered at its beginning and should
be extended to other portions of upper Sturla Valley;
indeed several geomorphological elements suggest a
wider extension of the studied phenomena, therefore
different areas of the valley on both riverbanks related
to the general overthrusting of Internal Liguride units
on the External ones could be involved.
ACKNOWLEDGEMENTS
The Authors would like to thank Dr. Flavio Pog-
gi, Regione Liguria, Dipartimento Ambiente, Settore
Assetto del Territorio, for having kindly provided the
numerical files of the digital earth model related to
the investigated area.
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