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Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
635
DOI: 10.4408/IJEGE.2013-06.B-61
THE 1963 VAJONT LANDSLIDE (NORTHEAST ALPS, ITALY)
POST-CONFERENCE FIELD TRIP (OCTOBER 10
TH
, 2013)
M
onica
GHIROTTI
(*)
, D
aniele
MASETTI
(**)
, M
atteo
MASSIRONI
(***)
,
e
Miliano
ODDONE
(****)
, M
ichele
SAPIGNI
(*****)
,
D
ario
ZAMPIERI
(***)
& a
nDrea
WOLTER
(******)
(*)
Alma Mater-Universitá di Bologna, Bologna, Italy
(**)
Universitá degli Studi di Ferrara, Ferrara, Italy
(***)
Universitá degli Studi di Padova, Padova, Italy
(****)
Dolomiti Project, Feltre, Italy
(*****)
Enel Produzione S.p.A., Venezia-Mestre, Italy
(******)
Simon Fraser University, Burnaby, British Columbia, Canada
K
ey
words
: Vajont Slide, stratigraphy, tectonics, geomorphology
INTRODUCTION
GEOLOGY OF THE BELLUNO BASIN AND THE
SOUTHERN ALPS
The Southern Alps are a large structural unit of the
Alpine chain located in Northern Italy (Fig. 1a). To the
North, the Southern Alps are separated from the main
body of the Alps by the major tectonic Periadriatic Line.
To the South, the crystalline and sedimentary rocks of
the Southern Alps are buried by the alluvial sediments
of the Po Plain. Along the Southern Alps, which extend
for about 700 km in an E-W direction, a tilted, nearly
ABSTRACT
The post-conference field trip focuses on the
Vajont reservoir landslide, one of the best known
examples of disasters induced by human activity;
it offers the possibility to appreciate the complex-
ity both of the surrounding area and of the particular
geological, structural and geotechnical features of
the landslide. The Vajont reservoir is located in the
SE part of the Dolomite Region of the Italian Alps,
about 100 km north of Venice. The doubly curved
arch dam stands 265.5 metres above the valley floor
and was the world’s highest thin arch dam when it
was built. On October 9
th
, 1963, during the third fill-
ing of the reservoir, a mass of approximately 270
million m
3
detached from the left side of the valley
and slid into the water at velocities up to 30 m/sec.
A wave subsequently overtopped the dam by 250 m
and swept into the Piave Valley below, resulting in
approximately 2000 deaths. The sliding lasted less
than one minute and produced seismic shocks, which
were recorded throughout Europe. Remarkably the
dam remained intact. The landslide moved mainly
along a chair-shaped failure surface, which corre-
sponded to a pre-existing slip surface as recognized
before 1963 by E. Semenza. The 1963 slip surface
was confined within 0.5–18 cm thick clay-rich lay-
ers, which were almost continuous over large areas
of the failure surface. The landslide was character-
ized by a long-term phase of accelerating creep last-
ing 2–3 years followed by the catastrophic failure.
Fig. 1 - a) The Mesozoic structural domains in the South-
ern Alps; b) the extensional Mesozoic architecture
of the Southern Alps at the end of the Early Creta-
ceous (redrawn and modified after B
ertotti
et alii,
1993; in F
antoni
& S
cotti
, 2003 for the western
and eastern sectors)
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M. GHIROTTI, D. MASETTI, M. MASSIRONI, E. ODDONE, M. SAPIGNI, D. ZAMPIERI & A. WOLTER
636
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
cipale was deposited, and separated areas with different
subsidence rates. To the west, shallow-marine calcaren-
ites, corresponding to a marginal facies of the Calcari
Grigi Group accumulating in the Trento Platform, were
deposited; in the east, dark cherty, basinal micrites
(Soverzene Formation) accumulated during Hettang-
ian–Pliensbachian time (Fig. 2). The pervasive dolomiti-
zation at the Triassic–Jurassic boundary, which affected
the oldest stratigraphic units of the Belluno Basin, pre-
vents accurate dating of this particular paleogeographic
unit of the Southern Alps. Nevertheless, based on data in
the Carnian Prealps, which represent the north-eastern
extension of the Belluno Basin and where sediments are
free from heavy dolomitization, the birth of the Belluno
Basin can be ascribed to the Triassic–Jurassic boundary
interval or even to the late Triassic.
SOVERZENE FORMATION (HETTANGIAN-PLIEN-
SBACHIAN; 600 METRES THICK)
This unit is about 600 m thick and is made of grey
and brown micrites that are commonly dolomitized,
are well stratified with beds 20-40 centimetres thick,
and alternate with thin levels of grey and yellow marls.
The carbonate mud is a mixture of pelagic sediment
and fine-grained material derived from the surround-
ing carbonate platforms (peri-platform oozes). Black
chert nodules are present, as are fossils of the Zoophy-
cos and Chondrites ichnogenera
. The lower half of the
unit is completely dolomitized and virtually devoid of
cherts; its uppermost portion constitutes a characteristic
horizon of white nodular calcarenites containing a rich
fauna of Ammonites and Aulacoceras (M
asetti
& B
i
-
anchin
, 1987). Many unconformable bodies of breccia,
consisting of cherty clasts embedded in dolomicrite,
cut the Soverzene Formation and the overlying Vajont
Limestone. According to Z
eMpolich
& h
arDie
(1997)
the emplacement of these bodies could be related to in
situ fracturing of the rock by means of late hydrother-
mal dolomitizing fluids.
IGNE FORMATION (TOARCIAN-BAJOCIAN; 0 TO
150 METRES THICK)
The formation is characterized by considerable
lithological heterogeneity. The succession, from bottom
to top, is as follows: a basal unit of alternating marls
and grey limestones with individual layers of 50 cm
thickness; a middle unit of laminated black shales and
Manganoan carbonates, recording the Early Toarcian
complete, crustal section is exposed (Fig. 1b). At the
westernmost end, deep continental crust rocks of the
Ivrea-Verbano Zone outcrop, while Mesozoic-Cenozo-
ic sedimentary covers characterize the eastern sector.
The sedimentary cover of the Southern Alps is consid-
ered a well-preserved section of the southern (Apulian)
continental margin of the Mesozoic Tethys, character-
ized by a horst and graben structure inherited from the
rifting associated with the opening of the basin in the
central North Atlantic. The rifting phase took place in
the late Triassic (Rhetic) and the Early Jurassic and cre-
ated high-standing blocks separated by troughs. The
western sector of the margin (Piedmont and Lombardy)
was rapidly flooded in the Early Liassic. In the eastern
Southern Alps three paleogeographical-structural units
are recognizable. These are, from west to east (W
inter
-
er
& B
osellini
, 1981): a carbonate platform, which was
flooded in the Early Jurassic, evolving into a pelagic
plateau with condensed sedimentation during the Late
Jurassic (Trento Platform/Plateau) and bordered to the
west by the Lombardy Basin; a basin that developed
in the Early Jurassic (Belluno Basin); and a carbonate
platform that persisted from the Jurassic till the Creta-
ceous (Friuli Platform).
THE BELLUNO BASIN
The birth of the Belluno Basin is linked to Early
Jurassic rifting that generated a fault system roughly
oriented N–S (M
asetti
& B
ianchin
, 1987). The faults
cut the wide peritidal platform where the Dolomia Prin-
Fig. 2 - Stratigraphic relationships of Mesozoic units out-
cropping in the Belluno Basin. 36-Dolomia Prin-
cipale; 35-Calcari Grigi, a) dolomitized, b) not
dolomitized; 34-Soverzene Formation; 33-Igne
Formation; 32-Vajont Limestone; 31a-Fonzaso
Formation; 31b-Rosso Ammonitico; 30- Bian-
cone; 29- Soccher Limestone; 28-Scaglia Rossa
(from c
oSta
et alii, 1996)
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THE 1963 VAJONT LANDSLIDE (NORTHEAST ALPS, ITALY) POST-CONFERENCE FIELD TRIP (OCTOBER 10
TH
, 2013)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
637
Fonzaso Formation is Callovian. During the Middle
Jurassic, deposition of the Vajont Limestone progres-
sively levelled the tectonically controlled submarine
relief of the Belluno Basin.
FONZASO FORMATION (CALLOVIAN-OXFOR-
DIAN; 10 TO 40 METRES THICK)
G
naccolini
(1968) named the succession between
the Vajont Limestone and the Scaglia Rossa the Soc-
cher Limestone. However, the classic units called the
Fonzaso Formation, Rosso Ammonitico and Biancone
in the Veneto area can be identified within this unit.
For this reason we preferred to adhere to the old for-
mational terms, using ‘Soccher Limestone’ only for
the Cretaceous succession, well-known everywhere as
Biancone. The Fonzaso Formation is formed by an in-
tercalation of thin beds of fine-graded biocalcarenites
with parallel and oblique laminations and dark micrites
very rich in chert. The micrite microfacies is character-
ized by radiolaria, often siliceous, and thin-shelled pe-
lagic pelecypods; the calcarenites come from the Friuli
Platform and contain neritic grains and fossils. The
cherty carbonate beds are intercalated with green clay
layers 0.5-18 cm thick, which acted as planes of weak-
ness in the movement of the Vajont landslide (Fig. 3).
These clay layers have been interpreted by B
ernoulli
& p
eters
(1970) as volcanic ash deposits widespread
in the Eastern Southern Alps. The formation does not
record important changes in depositional environment
oceanic anoxic event in the Belluno Basin (J
enkyns
&
c
layton
, 1986); and an upper unit of nodular limestones
in the Rosso Ammonitico facies corresponding to the
Hildoceras bifrons Zone, H. sublevisoni Subzone (Low-
er Toarcian) (J
enkyns
et alii, 1985). The upper boundary
of the Igne Formation is an erosional surface carved by
oolitic turbidites of the Vajont Limestone. In some areas
these erosive events obliterated the formation.
VAJONT LIMESTONE (LATE BAJOCIAN- BATHO-
NIAN; 450 METRES THICK)
One of the peculiar features of the Belluno Basin
is represented by the Vajont Limestone, composed of
oolitic sands and biogenic skeletal debris deposited by
means of gravity-flow processes that transferred mate-
rial from the western edge of the Friuli Platform into
slope and basin environments (B
osellini
& M
asetti
,
1972). This resedimented material consists of thick
beds of oolitic calcarenites intercalated with brown
basinal micrites and breccia formed by clasts ripped-
up from basinal micrites. Nodules of brown chert can
be locally present. The age of the Vajont Limestone
has been revised by c
oBianchi
(2002) using nanno-
fossil biostratigraphy performed on several sections
spanning the whole Toarcian–Tithonian interval. On
the basis of this study, the age of the Vajont Limestone
falls into the late Bajocian–Bathonian interval, since
the topmost part of the underlying Igne Formation be-
longs to the late Bajocian and the base of the overlying
Fig. 3 - a) Clay interbeds outcropping on the sliding surface; b) sketch of the Fonzaso Fm. outcropping southwest of Casso (from
H
endron
& P
atton
, 1985)
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M. GHIROTTI, D. MASETTI, M. MASSIRONI, E. ODDONE, M. SAPIGNI, D. ZAMPIERI & A. WOLTER
638
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
region. The present-day Vajont Valley represents the
base of the slope connecting the top of the Friuli Plat-
form to the basin floor. As clearly depicted in Fig. 2,
along the slope and at its base the pelagic, micritic sed-
iment (Biancone) was interlayered with resedimented
calcarenites and calcirudites coming from the Friuli
Platform. This close intercalation of pelagic micrites
and resedimented calcarenites, not present in the Bi-
ancone formation, represents the Soccher Limestone.
As mentioned above, this formational term has been
used here only for the Cretaceous succession. The fine-
grained deposits are made of thin-bedded cherty lime-
stones and grey, red, or greenish marls. These lime-
stones are locally nodular, exhibiting facies of Rosso
Ammonitico (Castellavazzo Marble). The presence of
many slump scars in the Soccher Limestone is further
evidence that the deposition of this unit took place
along the slope of the Friuli Platform.
SCAGLIA ROSSA
(UPPER CRETACEOS P.P. – LOWER PALEOCENE
P.P.; ABOUT 300 METERS THICK)
Red marls and red marly limestones, completely
devoid of resedimented deposits in the typical facies of
Scaglia. This formation records the levelling-up of the
pre-existing articulated topography.
FLYSCH (EOCENE; ABOUT 200 METRES THICK)
A thick succession of turbiditic arenites interlay-
ered with grey marls. The coarse fraction is represented
by calcarenites passing to grey or yellow litharenites.
compared to the Vajont Limestone: the most important
variations are related to the quantity (smaller) and to
the quality (bioclastic grains instead of oolites) of the
turbidites coming from the Friuli Platform.
ROSSO AMMONITICO (OXFORDIAN-TITONIAN;
5 -15 METRES THICK)
The Fonzaso Formation grades upwards into
nodular, micritic red limestones similar to the Rosso
Ammonitico Veronese (Upper Member, Upper Kim-
meridgian to Lower Tithonian). This unit consists of
reddish and grey, thick-bedded, nodular micritic lime-
stones, different only in colour from the classic facies
outcropping westward, in the Veneto area. This forma-
tion is virtually devoid of resedimented deposits and
the microfacies is characterized by peloidal pelagic
micrites bearing Saccocoma.
SOCCHER LIMESTONE (CRETACEOUS P.P.; 150
METRES THICK)
The Early Cretaceous palaeogeographic scenario
is characterized by an eastern, shallow-water domain
of the Friuli Platform facing the western, deep-sea area
including the Lombardy Basin, the Trento Plateau, and
the Belluno Slope (Fig. 2). At the end of the Jurassic
and during the Early Cretaceous, while shallow-water
sedimentation persisted on the Friuli Platform, the
deep-sea region of the Southern Alps was blanketed
by calcareous pelagic oozes, mostly consisting of nan-
nofossils. These white mudstones have been called
Maiolica in Lombardy and Biancone in the Venetian
Fig. 4 - Cross-section through the eastern Southern Alps (modified from d
oglioni
& c
arminati
, 2008). The grey rectangle
shows the Erto Syncline. Legend: B = crystalline basement; P – Tr = Permian-Triassic; J = Jurassic; K = Cretaceous,
T = Tertiary
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THE 1963 VAJONT LANDSLIDE (NORTHEAST ALPS, ITALY) POST-CONFERENCE FIELD TRIP (OCTOBER 10
TH
, 2013)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
639
and the two distinct lobes of the Vajont landslide. The
sliding mass was furthermore laterally constrained by
a system of subvertical faults (Croda Bianca and Col
Tramontin Lines to the east and west branch of the Col
delle Erghene Line to the west), while the rockslide
crown was constrained by E-W structures (Col delle
Erghene Line; r
iva
et alii, 1990).
FIELD TRIP STOPS
The stops on the field trip (Fig. 5) cover the geol-
ogy, stratigraphy, tectonics and geomorphology of the
Vajont Valley and their controlling effects on the 1963
landslide. Part of the field trip is dedicated to the main
structures that led to the development of and interfer-
ence between the Erto and Massalezza synclines, as
well as to their possible controlling effects on the 1963
sliding event, and part to geomorphological features
of large prehistoric landslides that dammed the valley.
STOP 1
PIAN DI VEDOIA: PANORAMIC VIEW OF THE BEL-
LUNO THRUST HANGING WALL.
Fig. 6 shows a view of the mouth of the Piave Val-
ley taken from Pian di Vedoia, on the right side, about
TECTONICS OF THE VAJONT VALLEY
The Vajont Valley follows the core of an Alpine
syncline (Erto Syncline) with an E-W to WNW-ESE
trending axis (F
erasin
, 1965; Riva et alii, 1990) gently
plunging towards the E (B
roili
, 1967). The Erto Syn-
cline lies on the hanging wall of the Belluno Thrust,
a main structure of the Venetian south-vergent Alps
(D
oGlioni
& c
arMinati
, 2008) and it is paired with
the frontal asymmetric anticline (Belluno Anticline)
(Fig. 4). The northern limb of the Erto Syncline (north
side of the valley) is reversed and stretched by the Mt.
Borgà Thrust, an older thrust passively transported on
the back of the Belluno Thrust.
The Vajont landslide reworked a paleo-landslide
covering the northern slope of the Mt. Toc (G
iuDici
&
s
eMenZa
, 1960; s
eMenZa
, 2010). Mt. Toc is structur-
ally located on the southern flank of the Erto Syncline
and is enclosed between two N-S to NNW-SSE strik-
ing and downward converging reverse fault systems
(Croda Bianca-Col Tramontin system and Col delle
Tosatte Fault). This peculiar structural setting has led
to the newly recognized N-S trending Massalezza Syn-
cline (M
assironi
et alii, this volume), which accounts
for an overall concave shape of the sliding surface
Fig. 5 - Field trip map
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M. GHIROTTI, D. MASETTI, M. MASSIRONI, E. ODDONE, M. SAPIGNI, D. ZAMPIERI & A. WOLTER
640
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
3 km north of Ponte nelle Alpi. To the right, Mt. Dola-
da corresponds to the forelimb of the Belluno anticline,
associated with the south-verging Belluno thrust. In
the background (to the left), the Mt Borgà Thrust out-
crops on the right side of the Vajont Valley.
STOP 2
PODENZOI: THE LEFT SIDE OF THE PIAVE VALLEY
Panoramic view of the left side of the Piave Valley
(Fig. 7). In the upper part of the slope the southern limb
of the Erto Syncline and the Vajont sliding surface are
prominent. In the lower part of the slope the Col delle
Tosatte Fault is seen. It is a west-verging reverse fault
cutting the base of the Erto Syncline (see Stop 6).
STOP 3
CASSO: SIGHT OF THE LANDSLIDE
From the village of Casso, just in front of the slide,
we can appreciate the entire landslide. The landslide in-
volved Jurassic and Cretaceous rocks (limestones and
marls) with varying degrees of fracturing. Movement
occurred along a chair-shaped failure surface in part cor-
responding to a pre-existing slip surface at or close to
residual strength as indicated by the geological evidence
recognized before 1963 (s
eMenZa
& G
hirotti
, 2000).
The failure zone was largely confined to 0.5-18 cm thick
clay-rich layers (h
enDron
& p
atton
, 1985) that were
observed to be continuous over large areas of the failure
surface. Geological and tectonic evidence suggests that
both the 1963 landslide and the prehistoric one are lim-
ited by one or more faults (h
enDron
& p
atton
, 1985).
During the third reservoir emptying operation,
the northern slope of Mt. Toc failed suddenly over a
length of 2 km and a surface area of 2 km
2
. The slide
moved a 250 m thick mass of rock some 300 to 400 m
horizontally (Fig. 8a) with an estimated velocity of 20
to 30 m/s, before running up and stopping against the
opposite side of the Vajont Valley. The majority of the
slide moved as a whole and reached the opposite side
of the valley without any change in shape apart from
a general rotation evident from both the surface mor-
phology and the stratigraphical sequence that remained
essentially unchanged after the movement (Fig. 8b).
G
iuDici
& s
eMenZa
(1960) discussed the geology in
detail and put forward the hypothesis of the existence
of a very old landslide on the left bank of the Vajont
reservoir area. During their surveys they discovered
a highly fractured zone (“mylonite”) extending about
1.5 km along the left side of the valley corresponding
to the sliding plane of the prehistoric landslide (G
hi
-
rotti
, 2012). Nevertheless, the dam designers con-
cluded that a deep-seated landslide was very unlikely
to occur, mainly because of both the asymmetric form
of the syncline, which was expected to act as a natural
obstacle for possible slope movements, and the good
quality of in situ rock masses, as derived from seismic
surveys (M
üller
, 1964, 1968, 1987).
STOP 4
CASSO: THE CLAY INTERBEDS OF THE FONZA-
SO FM
Today, it is generally agreed that 1963 failure
occurred mostly along planes of weakness repre-
sented by clay-rich interbeds (Fig. 3) within the
Fonzaso Formation (h
enDron
& p
atton
, 1985;
T
ika
& h
utchinson
, 1999; F
erri
et alii, 2011).
However, the continuity and the existence itself
of clay interbeds in the calcareous sequence repre-
Fig. 6 - View of the mouth of the Piave Valley taken from Pian di Vedoia. Legend: DP = Dolomia Principale (Upper Triassic);
CV = Vajont Limestone (Middle Jurassic); FF = Fonzaso Fm + Rosso Ammonitico (Middle-Upper Jurassic); CS = Soc-
cher Limestone (Cretaceous); SR = Scaglia Rossa (Upper Cretaceous-Lower Tertiary) (Photo by D. Zampieri)
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THE 1963 VAJONT LANDSLIDE (NORTHEAST ALPS, ITALY) POST-CONFERENCE FIELD TRIP (OCTOBER 10
TH
, 2013)
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Editrice
641
increase in pore water pressure due to the raising of
the water level in the reservoir caused a decrease
in effective normal stress, favouring the sliding on
these clay layers characterised by a residual friction
angle φ
r
between 8° and 10°. Clay interbeds are well
exposed in an outcrop southwest of Casso.
sented a controversial aspect for many decades. The
statement that “...the succession does not include
any clay beds or intercalations which some authors
consider may have been responsible for some as-
pects of the phenomenon
” (M
üller
, 1968) was de-
finitively dismissed only after 1985 with the work
of h
enDron
& p
atton
(1985). For these authors, the
Fig. 8 - a) The failure scar and the deposit of the 1963 slide (Mount Toc behind) (from g
Hirotti
, 2012); b) aerial photo few
days after the slide: toponyms are highlighted (modified after S
elli
et alii, 1964)
Fig. 7 - Panoramic view of the left side of the Piave Valley, overlooking Longarone (Photo by D. Zampieri)
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M. GHIROTTI, D. MASETTI, M. MASSIRONI, E. ODDONE, M. SAPIGNI, D. ZAMPIERI & A. WOLTER
642
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
by the 1963 landslide and suffered only minor damag-
es. The Vajont Dam withstood a load eight times greater
than it was designed to withstand. Engineers who built
the Vajont Dam were working toward a masterpiece in
engineering history, which they achieved.
STOP 6
VAJONT GORGE AND THE COL DELLE TO-
SATTE FAULT
Within the Vajont gorge, downstream of the dam,
the Col delle Tosatte Fault outcrops (Fig. 10a). It is
clear from the field as well as from historical pho-
tographs (A-11 and A-25 in M
asé
et alii, 2004) that
this fault unambiguously dips towards the east and
is a westward-directed reverse fault. The fault is as-
sociated with a ramp anticline deforming the Liassic
STOP 5
WALK ON THE CROWN OF THE DAM
The walk on the crown of the Vajont Dam (con-
structed between 1957 and 1960) gives the possibility
to observe the dam itself, which was at that time the
highest thin arch dam in the world. The doubly curved,
265.5 m-high arch dam (Fig. 9) has abutments an-
chored in the steep flanks of the deep canyon that cuts
limestones of Malm and Dogger age. The planned full
reservoir capacity was a volume of 169 million m
3
. Re-
markably, the thin arch dam resisted the forces imposed
Fig. 10 - a) Panoramic view of the right side of the Vajont
gorge, downstream of the dam; b) sketch of the Col
delle Tosatte Fault cropping out on the right side
of the Vajont gorge; c) plot (lower hemisphere) of
mesoscale reverse faults collected close to the main
fault (after m
aSSironi
et alii, in this volume)
Fig. 11 - The interference between folds related to the Erto
(E-W to WNW-ESE) and Massalezza (N-S to NNW)
synclines: a) Meso-scale refolded folds on the
sliding surface at Massalezza; b) Meso-scale re-
folded folds on the sliding surface of the western
lobe (continuous line = hinges of the Massalezza
syncline fold set; dashed line = hinge of The Erto
syncline fold set); c) Top: Interference pattern after
r
amSey
(1967) (left) and t
HieSSen
& m
eanS
(1980)
obtained by considering the average axes trends
and axial planes of the Massalezza Syncline and
Erto Syncline sets. Bottom: Contour plot (equal-ar-
ea lower-hemisphere) of the fold axes on the sliding
surface (after m
aSSironi
et alii, this volume) (Photo
by M. Massironi)
Fig. 9 - The Vajont Dam
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THE 1963 VAJONT LANDSLIDE (NORTHEAST ALPS, ITALY) POST-CONFERENCE FIELD TRIP (OCTOBER 10
TH
, 2013)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
643
which originated the multiple steps that are observed
on the failure surface. All of these elements, mainly
pre-dating any gravitational event on the Mt.Toc north-
ern slope, may have played a significant role in failure
behaviour and may also be used to model the landslide
with two- and three-dimensional codes.
STOP 8
MESAZZO SECTION
The stratigraphy mapped by r
ossi
& s
eMenZa
(1965) outcrops in the Mesazzo Valley. The original
maps present the stratigraphy as a simple succession.
In reality, it may be complicated by folding and fault-
ing. All the tectonic lines of greater interest are oriented
roughly E-W with a small angle and involve extensive
movement producing the repetition of the stratigraphic
sequence several times.
LA PINEDA LANDSLIDE
There are quaternary sections of extraordinary
beauty at the confluence of the Mesazzo Stream and Va-
jont River. The Pineda deposit located east of the Vajont
Slide is an example of prehistoric mass movements in
the Vajont Valley. It has been hypothesized to originate
from either the north or south slope of the valley, but the
most widely accepted view is that its source area is the
steep, bare slope on the north slope (Fig. 13).
The landslide would have dammed the Vajont River
and Mesazzo Stream, with implications for river course,
erosion of the landslide dam, and evolution of the valley
geomorphology. The Pineda Landslide overlaps a delta
sequence (topset, foreset, bottomset) of glaciofluvial
origin, allowing its preservation. This delta entered a
Igne Formation, at present overlying the Cretaceous
Soccher sequences (Figs. 10b, 10c). At the Col delle
Tosatte Fault footwall a minor splay has been found;
it is associated with a ramp anticline in the hanging
wall and an asymmetric syncline in its footwall, both
involving the Soccher sequence and Scaglia Rossa
Formation (Figs. 10b, 10c).
The westward propagation of this fault is distinc-
tive with respect to the south-vergent Belluno Thrust
and related folds (Stop 1) and suggests a different ori-
gin for this structure: it could be an inherited Dinaric
thrust or alternatively the result of a transpressional re-
activation of a pre-existing Mesozoic fault during the
Alpine convergence. This peculiar fault is structurally
related to the N-S striking Massalezza Syncline, which
strongly affected the failure surface (Stop 7).
STOP 7
SLIDING PLANE AT MASSALEZZA CREEK
The Vajont landslide occurred on the southern limb
of the Erto Syncline, which dips 30° to 50° towards the
NNE and N. The sliding plane has an overall concave
shape with the eastern and western lobes converging to-
ward Massalezza Creek, which coincides with the hinge
of the Massalezza Syncline. The result is that the Vajont
failure surface is everything but sharp and smooth. The
E-W to WNW-ESE folds and related joints are respon-
sible for several structural terraces (the most prominent
one affecting the eastern lobe) and monoclines (see also
B
roili
, 1967 and h
enDron
& p
atton
, 1985), whereas
the N to NNW trending undulations (axes average
trend/plunge: N010°/40°), often control gully incisions,
particularly in the western lobe of the sliding surface
(see also h
enDron
& p
atton
, 1985). Parasitic folds
tend to increase towards the hinges of the main folds;
hence, the most tectonized sector of the sliding plane is
downstream of Massalezza Creek where the hinges of
the Erto and Massalezza synclines interfere with each
other (Fig. 11). The E-W to WNW-ESE folds affecting
the Fonzaso Fm. beds frequently display flexural slip
processes generating meso-scale flat-ramp thrusts verg-
ing towards the south (Fig. 12). These anti-gravitational
kinematics suggest that the E-W to WNW-ESE folds
are unrelated to gravitational events. Similarly, the ori-
entation of the Massalezza-related poly-harmonic folds
exclude any gravitational origin.
In summary, the orientation of the failure sur-
face is the product of at least two episodes of folding,
Fig. 12 - Flexural slip processes generating meso-scale
flat-ramp thrusts verging towards the south (Pho-
to by D. Zampieri)
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644
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
now-extinct glacial lake, as witnessed by laminite se-
quences with drop-stones (Fig. 14). There is a diamictite
deposited on the Pineda landslide, hypothesized to be
glacial till. This would point to a pre-Pleistocene age for
the Pineda. However, recent field investigations were
inconclusive. It was likely not the only large prehistoric
landslide to dam the valley. Other movements include
the prehistoric Vajont and Monte Borgà failures.
STOP 9
THE NOVE HYDROELECTRIC POWER PLANT:
THE PHYSICAL-HYDRAULIC MODEL
Soon after the discovery of the paleo-landslide by
G
iuDici
& s
eMenZa
(1960), the project engineers decided
to build a physical model of the left slope of the Vajont
Valley; it was not a landslide model but rather a model
to simulate the hydraulic effects of mass movement into
the reservoir. This was the first model of a landslide ever
built in the world and it reproduced the dam, the valley
and the landslide at a 1:200 scale (G
hetti
, 1962).
In the first series of experiments, the model consti-
tuted a uniformly inclined (30°) wooden surface plank
covered with sheet metal; the landslide mass was made
up of gravel retained by flexible wire mesh and the fall
was simulated by the sudden release of the contain-
ing mesh (Fig. 15). Semenza, who assisted in the first
experiment on August 30 1961, suggested modifying
the model so that the movement surface was similar
to that of the actual landslide (Fig. 16). The requested
Fig. 13 - Most likely source area of the Pineda Landslide. The
deposit is in the middle ground, whereas the source
area is in the background (Photo by A. Wolter)
Fig. 14 - Photo of E. Semenza dated July 1959 (from MASÈ
et alii, 2004). The original caption of the picture
stated: the left bank of the lower Mesazzo Valley,
seen from the right bank below Case Prada (el.
700 m a.s.l. approx.); on the right the village of
Erto and the Zemola Valley. From top to bottom
can be recognized: Dogger debris and cataclasite,
conglomerate with local cross-bedding, alluvial
uncemented deposits and steeply inclined Flysch.
The conglomerate present on the right bank is also
visible at the left edge of the photo; the alluvial
deposits are present on the right bank, on the right
side of the photo near the old house
Fig. 15 - Original photo n.10, the landslide mass of gravel
resting on the sliding surface, held in place by
hemp nets and ropes, before a test of the second
series (from g
Hetti
, 1962)
Fig. 16 - Original photo n.6, building of the concave
shaped sliding surface (from g
Hetti
, 1962)
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THE 1963 VAJONT LANDSLIDE (NORTHEAST ALPS, ITALY) POST-CONFERENCE FIELD TRIP (OCTOBER 10
TH
, 2013)
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
645
The experiments were carried out with fall times
ranging from several minutes (similar to the Pontesei
landslide of 1959) down to one minute (equal to about
4.24 seconds in the model). Note that many technicians,
in the years following the 1963 landslide, stated that if
the model had simulated the actual velocity (two seconds
in the model equal to 25 seconds in real time), the result-
ing wave would have corresponded to that of reality.
modifications were implemented based on a series of
geological profiles provided by Semenza.
The gravel constituting the landslide mass was
stiffened with rigid vertical sectors which were
pulled by a tractor (Figs. 17, 18). This allowed, in
spite of the chair-like form of the basal sliding sur-
face, both the displacement of the entire landslide
mass as a unique body and the movement of the mass
with variable velocities at will.
Fig. 17 - Original photo n.9, caterpillar tractor with the
traction cables, is ready to cause the controlled
movement of the slide (from g
Hetti
, 1962)
Fig. 18 - Part of the original plate N.2, drawing of the pull-
ing system of the various sectors immersed in the
gravel mass during the second series of tests (from
g
Hetti
, 1962)
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