Document Actions

ijege-13_bs-wolter-et-alii-2.pdf

background image
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
613
DOI: 10.4408/IJEGE.2013-06.B-59
AN ENGINEERING GEOMORPHOLOGICAL CHARACTERISATION
OF THE 1963 VAJONT SLIDE
A
ndreA
W
olter
, d
oug
S
teAd
, B
rent
C. W
Ard
& J
ohn
J. C
lAgue
Simon Fraser University - Burnaby, Canada
INTRODUCTION
Geomorphological factors contributing to slope
instability are typically complex and interrelated.
They include slope angle, weathering, freeze-thaw
cycles, river incision, and glacial erosion. The study
of these processes and their effects is critical in un-
derstanding not only regional landscape evolution but
also the development of individual slopes, which may
be the sites of engineering projects.
Engineering geomorphology developed as a disci-
pline in recognition of the importance of surface proc-
esses and landforms to anthropogenic modifications of
the Earth. It involves the application of geomorpho-
logical theory and methods to engineering activities and
provides spatial context for engineering concerns, an
assessment of the impact of engineering on the environ-
ment and landscape, and an evaluation of the risks and
implications of landform change for society (G
IARDINO
& M
ARSTEN,
1999; F
OOKES
et alii, 2005, 2007). In es-
sence, the discipline endeavours to interpret geomor-
phological features, their interrelationships, and their
evolution as applied to engineering works. An important
aspect of this interpretation is the consideration of time
on both engineering and geological scales, and an evalu-
ation of dynamic processes and landform evolution as
they affect engineering projects (G
RIFFITHS
et alii, 2012).
The 1963 Vajont Slide, which is located just up-
stream of the Vajont Dam in northeastern Italy, has been
studied extensively over the past 50 years. Research has
highlighted the lithology, hydrogeology, kinematics and
ABSTRACT
The 1963 Vajont Slide is one of the most studied
natural disasters in the world, with over 150 publica-
tions on its cause, mechanisms, behaviour, and effects.
Most of these studies have considered the event from
a descriptive, engineering geology, structural geology,
or geophysical perspective, and the geomorphology
of the Vajont Slide and the Vajont Valley has been
neglected in all but a few papers. Nonetheless, geo-
morphological features and processes provide valu-
able insights into the preconditions and movement of
the landslide. This paper presents the first engineering
geomorphological maps of pre- and post-slide topog-
raphy and their interpretation. The maps show chang-
es in slope morphology, which indicate boundaries of
landforms, and relationships between these landforms.
Our interpretations support previous hypotheses, such
as the existence of an ancient landslide in the same
location as the 1963 event and the intact nature of the
sliding mass. In addition, the landslide is proposed to
have moved in two main blocks, with a possible third
block on the west margin of the slide. A classification
of failure scar morphology illustrates the implications
of geomorphological features for failure behaviour,
and the interaction between tectonic and geomorphic
processes to precondition and degrade the slope to the
point of failure is highlighted.
K
ey
words
: Vajont Slide; engineering geomorphology; mor-
phological maps; characterisation
background image
A. WOLTER, D. STEAD, B.C. WARD & J.J. CLAGUE
614
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
REGIONAL GEOMORPHOLOGICAL AND
STRUCTURAL SETTING
Vajont Valley has relief of approximately 1500 m,
with the highest peak, Monte Borgá, reaching an eleva-
tion of over 2200 m asl. The rocks within the valley
have been subjected to tectonic deformation, uplift, and
glacial and fluvial erosion, but the evidence of these
processes has been largely obscured by weathering,
karstic processes, and mass wasting. g
uerriCChio
&
M
elidoro
(1986) summarise the history of landslides
in the valley, including the Pineda, Monte Borgá, Co-
lomber, and Vajont failures. They note that the Vajont
River has been repeatedly dammed by these large
events. An example is the Pineda deposit, which is ad-
jacent to the Vajont Slide at the confluence of the Vajont
and Mesazzo rivers. It has been incised by both rivers
to form steep erosion scarps in intact rock strata and
diamicton (Fig. 1). The deposit’s location at the bottom
of the valley and the flow of streams around it also in-
dicate that it blocked the valley. C
oppolA
& B
roMheAd
(2008) discuss the stability of landslide dams in the Do-
lomites, as well as their significance to river morphol-
ogy and application to hydroelectric power projects due
to the increase in hydraulic head across the dams.
Another process that has importance for slope
stability in the region is carbonate dissolution. H
EN-
DRON
& P
ATTON
(1985) and G
UERRICCHIO
& M
ELIDORO
(1986) refer to a karstic plain with scattered dolines
above the Vajont Slide, which they identified on air-
photos. We could not verify this interpretation, but
we did observe a relatively flat and hummocky area
above the Massalezza catchment (Fig. 1). Rock pin-
nacles and caves in the area, however, are consistent
with karstic topography. The Croda Vasei above the
Vajont Slide (Fig. 1) may be a remnant karst tower, as
it is undercut and contains fissures and caves. Several
gullies in the Vajont Valley are also dry and terminate
abruptly, consistent with the presence of karst.
Evidence of Pleistocene glaciation includes the
broad floor of the Vajont Valley and scattered gla-
cial deposits. A glacier in the Vajont Valley presum-
ably would have been confluent with a larger glacier
in nearby Piave Valley, which has been documented
by C
AStiglioni
(1940). Glaciation of the valley would
serve to remove old landslide debris and oversteepen
valley walls. An epigenetic gorge over 250 m deep
and less than 30 m wide at its base marks the mouth
to the Vajont Valley (Fig. 1). The origin of the gorge
dynamics, and effects of the slide. The geomorphology
of the area has been largely neglected, although some
papers describe the geomorphological setting of the
event (G
IUDICI
& S
EMENZA
, 1960; C
ARLONI
& M
AZZANTI,
1964a, 1964b; S
ELLI
& T
REVISAN
, 1964; R
OSSI
& S
EMEN-
ZA
, 1964, 1965; B
ROILI
, 1967; S
EMENZA
, 1967; H
ENDRON
& P
ATTON
, 1985; & G
UERRICCHIO
& M
ELIDORO
, 1986).
Most of these studies discuss the geomorphological fea-
tures related to an ancient landslide at the same location
as the 1963 event. S
EMENZA
(2001) provides a palinspas-
tic reconstruction of the north slope of Monte Toc from
before the paleo-slide to present, and P
ARONUZZI
& B
OL-
LA
(2012) update Semenza’s slope reconstruction with a
new geological model. B
ROILI
(1967) emphasises the slip
surface geometry and properties of the 1963 landslide,
in particular irregularities related to tectonic features and
the role of clays. H
ENDRON
& p
Atton
(1985) examined
airphotos to determine whether or not an ancient slide
could have been recognised prior to 1963; they conclude
that, given the multiple scarps, depressions, and linea-
ments, the slide should have been identified. They pro-
duced the first geomorphological map of the slide area,
illustrating scarps, depressions, streams, sinkholes, and
gullies that are identifiable on the 1960 pre-slide airpho-
tos. Only G
uerriCChio
& M
ELIDORO
(1986) focus exclu-
sively on geomorphology. They describe the southern
and northern slopes of the Vajont Valley in the area of
the 1963 slide, and provide sketches and maps of proc-
esses and landforms such as prehistoric and recent mass
movements, as well as catchment and drainage maps.
They also describe the geological history of the valley,
including the development of a tectonic décollement on
the northern slope of Monte Toc.
In this paper, we provide an engineering geomor-
phological perspective on the Vajont Slide based on
preparation and interpretation of detailed pre- and
post-1963 morphological and morphogenetic maps.
The morphological maps show changes in slope that
delineate boundaries between landforms, and mor-
phogenetic maps enable interpretations of landform
relationships and evolution. This perspective supports
many previous findings on the slide and highlights
some aspects of the event that have not previously
been documented. Our objectives are to:
i. infer landslide behaviour from surficial expressions
of geomorphological processes, and
ii. identify geomorphic controls and preconditions on
the 1963 Vajont Slide.
background image
AN ENGINEERING GEOMORPHOLOGICAL CHARACTERISATION OF THE 1963 VAJONT SLIDE
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
615
to create complex basin and dome structures. Several
faults define the valley. The Monte Borgá overthrust
dominates the north valley wall and is the initiation
site of the Monte Borgá landslide. The steep north-
dipping Col delle Erghene Fault delimits the west
margin of the headscarp of the 1963 Vajont Slide, and
the east side of the scarp is bounded by the west-dip-
ping Col Tramontin Fault. This fault is a splay of the
Croda Bianca Fault.
Although many valleys in the Dolomites have
similar geomorphological and structural settings to
the Vajont Valley, the combination of these factors
at Vajont is responsible for the high number of cata-
strophic failures there.
METHODOLOGY
Fig. 2 illustrates the methodology we employ in this
paper. Analysis began with the interpretation of aerial
has not yet been adequately explained, although it
could be a hanging valley or a bypass drainage route
resulting from blockage of the mouth of the valley by
a landslide. Given the geometry of the gorge and the
numerous large instabilities that have dammed the
valley, the latter explanation is more likely.
Most of the landforms mentioned above are con-
trolled by tectonic structures. The Vajont Valley fol-
lows the Erto Syncline plunging 20° to the east, the
southern limb of which defines the characteristic
chair-shape of the north wall of Monte Toc (M
ASSIRONI
et alii, this volume; Fig. 1). The Erto Syncline transi-
tions into the Belluno Anticline at the peak of Monte
Toc, and the karstic plain referred to above follows
this transition. The Massalezza Gully marks the axis
of a north-plunging syncline (W
OLTER
et alii, in re-
view; M
ASSIRONI
et alii, this volume). These two fold
generations interfere on the south side of the valley
Fig. 1 - Geomorphological features of the Vajont Valley. a) The Pineda landslide deposit exposed along Mesazzo Stream;
intact strata and diamicton are visible. b) Fissures and caves in the remnant karst tower Croda Vasei. c) Hummocky,
less steep area behind the Vajont Slide that H
endron
& P
atton
(1985) referred to as a karstic plain. d) Photogramme-
try model profile of the north slope of Monte Toc as seen from Longarone. The profile shows the characteristic chair
associated with the Erto Syncline and the narrow gorge at the mouth of the Vajont Valley
background image
A. WOLTER, D. STEAD, B.C. WARD & J.J. CLAGUE
616
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
whereas the pre-event map displays only features tens
of metres or larger in size. The morphological maps
are strictly descriptive; they provide the foundation
for the interpretive morphogenetic maps.
MORPHOGENETIC MAPS
Examination of the pre-event morphological map
indicates that active processes on the north slope of
Mount Toc prior to the 1963 catastrophic failure in-
clude gullying, fluvial erosion, and surficial landslid-
ing. Surficial landslides occurred on gully walls and at
the toe of the slope where it is undercut by the Vajont
photographs from before (1960) and after (1963, 2004)
the catastrophic failure. We completed detailed field
mapping in 2010 and 2011 along roughly north-south
transects at 50-m spacing (Fig. 3). Both the airphoto
interpretation and field mapping focused on the slide
area and were corroborated by interpretation of LiDAR
DEMs. Abrupt concave and convex slope breaks and
gradual changes in slope were extracted from the field
traverses, airphotos, and DEMs. Slope angles were
measured in the field with a clinometer and are point
data rather than average values. Following recommenda-
tions by the g
eologiCAl
S
oCiety
in
l
ondon
(1982), we
estimated the relative ages and evolution of landforms
visible on interpretative morphogenetic maps. The pre-
and post-1963 maps were created at different scales: the
pre-event map is at a smaller scale (of the order of 1:20
000), because it was created from small-scale airphotos;
the post-event map has a larger scale (approximately
1:3000) as it incorporates field mapping, LiDAR, and
observations derived from larger scale airphotos. We
also briefly document the regional geomorphology us-
ing the airphotos and field observations.
RESULTS AND DISCUSSION
MORPHOLOGICAL MAPS
The pre- and post-event morphological maps are
shown in Figs. 4 and 5 respectively. The difference
in the observation scales mentioned above is evident
from a comparison of the two maps. The post-event
field map shows features at metre-scale and larger,
Fig. 3 - Map of field traverses spaced 50 m apart (black lines) within the mapping area (white dashed line). The two faults
controlling the 1963 failure are indicated by red dashed lines. The inset shows the location of the Vajont Slide in
northeastern Italy
Fig. 2 - Flowchart of methods used to create the morpho-
logical and morphogenetic maps and to make
engineering geomorphological interpretations of
landform evolution and processes that informed
numerical modelling. Numerical modelling is
presented in another paper (W
olter
et alii, in this
volume), and hence this step in the flowchart is
outlined with a dashed rectangle
background image
AN ENGINEERING GEOMORPHOLOGICAL CHARACTERISATION OF THE 1963 VAJONT SLIDE
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
617
Fig. 4 - Pre-slide morphological map derived from the 1960 airphotos. Symbols represent changes in slope, as recommended
by the G
eoloGical
S
ociety
in
l
ondon
(1982). The inset is a slope map of the pre-1963 slide area. The sub-horizontal
(green) areas are discussed in the text
Fig. 5 - Part of the post-slide morphological map. The 2004 orthophotos are shown for reference. The inset shows the location
of the mapped area. Symbols represent changes in slope (see Fig. 4)
background image
A. WOLTER, D. STEAD, B.C. WARD & J.J. CLAGUE
618
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
River. Relict landforms such as eroded landslide depos-
its illustrate the palimpsestic history of the slope. The
map also reveals several benches that we interpret to
be products of the ancient landslide (Fig. 6). The larg-
est bench, the Pian della Pozza, is about 500 m long
and 300 m wide. The smallest bench, located at the
east side of the headscarp of the 1963 failure, had an
area of approximately 1300 m
2
. The paleo-landslide
appears hummocky on the airphotos, especially east of
the Massalezza Gully. Our identification of the ancient
landslide on the 1960 airphotos supports H
ENDRON
&
P
ATTON
’s (1985) statement that it could have been rec-
ognised before the catastrophic failure in 1963 had a
thorough site assessment been conducted. The evidence
is clear: hummocky ground, scarps, ridges, and active
surficial landslides suggest previous as well as ongoing
slope movement in 1960. Settlements, agriculture, hor-
ticulture, road construction, and dam construction have
also modified the landscape, but it is unclear how exten-
sively. For example, the pseudo-benches (with slopes
between 10° and 20°) east of the Massalezza Gully sys-
tem (indicated by ‘p’ on Fig. 6) have steeper slopes than
the sub-horizontal benches west of the gully; they may
be undulating topography or discrete blocks produced
by the paleo-slide or flatter ground exploited for farm-
ing, homes, or cut-and-fill construction. Given the long
history of settlement in the Vajont Valley, evidenced,
for example, by remnants of Roman roads (H
ENDRON
&
P
ATTON
’S, 1985; S
EMENZA
, 2001), any of these explana-
tions is possible. The most likely explanation, however,
is landsliding. The average elevations of some of the
benches are similar, but it is unclear whether or not
these benches were once connected, and have since
been separated by the Massalezza Gully. Slope angles,
however, suggest that most benches were not connected
in the past. For example, the Pian della Pozza bench is
sub-horizontal and tilts slightly into the slope, whereas
the large pseudo-bench east of the Massalezza Gully
dips down-slope. It is unlikely that these would have
once been a single landform.
Several steep scarps attest to instability of the south
Vajont Valley wall. Two of these scarps are WNW-ESE
trending lineaments above the highest benches and co-
incide with the Col delle Erghene Fault. A third scarp
Fig. 6 - Interpretation of pre-slide landforms and processes. “p” denotes inclined benches.
background image
AN ENGINEERING GEOMORPHOLOGICAL CHARACTERISATION OF THE 1963 VAJONT SLIDE
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
619
posit front and are especially common along the steep
faces of the failure scar. In the field, we identified a
relatively large new slide deposit that post-dates the
2004 imagery. Its source is the secondary scarp near
the central lower portion of the failure scar east of the
Massalezza Gully. The Col Tramontin Fault, which
marks the east margin of the 1963 landslide, is another
area of active erosion. A gully lies between the fault
wall and the landslide debris and conveys sediment
ranging in size from clay to boulders.
Other processes that have altered the 1963 land-
slide scar include piping, ponding, and road construc-
tion. Piping-related collapse is indicated by a cluster
of circular depressions between 30 and 50 m in di-
ameter and 10 to 20 m deep (Fig. 5) near the left side
of the dam, which S
EMENZA
(1967) named “Costa dei
Crateri”. These features appeared shortly after the
1963 slide and are still obvious today. Other smaller
collapse features are scattered along the front of the
deposit. Displacement wave water accumulated in a
large depression behind the landslide front located at
the hinge of the Erto Syncline between the failure scar
and the deposit front. The so-called Massalezza Lake
has since drained and partially infilled with sediment,
leaving a wetland. Construction of the new road sys-
tem has modified parts of the slide deposit.
IMPLICATIONS FOR THE 1963 FAILURE
The behaviour of the Vajont Slide can be inferred
from its morphology. The intact nature of the displaced
mass is evident from similarities in the pre- and post-
event topography: benches and other features that can
be seen on the 1960 photos are preserved, although
displaced, on the post-event imagery. In particular,
preservation of the Massalezza Gully within the 1963
slide deposit suggests a rigid displaced body that must
have slid on a relatively thin, weak layer, rather than
fragmenting. The hypotheses that the 1963 slide was
a reactivation of an old slide and that clay interbeds in
the rock slope were at residual strength at failure are
supported by this geomorphic evidence.
As H
ENDRON
& P
ATTON
(1985) described, the east
half of the landslide is morphologically and behaviour-
ally different from the west. The slide block on the east
is hummocky with curvilinear ridges and depressions
that contain ponds (Fig. 7). The material forming this
block was compressed, and its location above the rest
of the displaced mass indicates that it moved after the
is located just below the scarp east of the Massalezza
Gully. Collectively, the three scarps approximately de-
lineate the 1963 slide headscarp. Another, smaller scarp
is located within the Pian della Pozza bench. It is likely
a tension crack related to a slide in 1960.
A distinctive feature on the pre-1963 morphologi-
cal map is the depressions in the palaeo-slide debris.
The largest depression, located west of Massalezza
Gully on the Pian del Pozza, comprises several semi-
circular hollows. It is probably karstic in origin, and
may have been exploited by the paleo-landslide and
acted as a drainage sink. A similar cluster of semi-
circular hollows is present near the western edge of
the 1963 slide deposit (see below).
Relationships between the landforms identified
on the pre-1963 morphogenetic map are complex.
Several gullies appear to be relict, inactive features
with mature vegetation. The Massalezza tributaries,
however, remain active, with clear channel beds and
evidence of gully wall erosion. The Massalezza Gully
is either younger than the ancient slide, and has bi-
sected an originally continuous deposit, or it could
have acted as a lateral release to both the east and the
west halves of the slide. The mouth of the gully may
have failed, and the stream could subsequently have
re-established its path. Another hypothesis is that the
gully-slide relationship was the same as of the 1963
failure and gully: the gully could have failed with the
slide, but remained intact (see below). The gully sys-
tems in the east are most likely associated with the
Col Tramontin/Croda Bianca Fault zone. The surficial
landslides at the toe of the slope appear fresh and are
most likely related to fluvial undercutting and reser-
voir filling. The location of the November 1960 slide
is apparent on the 1960 airphotos, which were flown
before the failure.
The post-event morphogenetic map shows many
of the same processes as the pre-event map. Gullying
is common, but not in the same locations as before
the catastrophic failure. The active gullies identified
on the pre-event airphotos appear to be inactive on the
2004 orthophotos. Since 1963, gullies have formed in
material that has moved down-slope. Talus cones lo-
cated at the hinge of the Erto Syncline are associated
with these gullies. The Vajont River no longer erodes
the northern slope of Monte Toc behind the dam; it
was redirected through the bypass tunnel constructed
in 1961. Surficial landslides still occur along the de-
background image
A. WOLTER, D. STEAD, B.C. WARD & J.J. CLAGUE
620
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
bris, and fine debris (Fig. 8). The failure zone consist-
ed of coarse and fine debris and few areas of bedrock
immediately after the event (Fig. 8). The coarser de-
bris visible today appears to be older and more stable
than the fine debris. The vegetated areas are also more
stable than the fine debris and represent either blocks
of material that remained intact during the 1963 slide
or more cohesive blocks that were easily revegetated.
Finally, the surface morphology of the slide debris
allowed us to identify zones of compression and exten-
sion (Fig. 7). The most obvious zone of extension is the
depression behind the front of the deposit, roughly par-
allel to the axis of the Erto Syncline, where the Massal-
ezza Lake formed. As already mentioned, the east block
is hummocky with transverse ridges, suggesting com-
pression. These ridges are up to several metres high and
several tens of metres long. In contrast, ridges near the
front of Block A are smaller, suggesting that the block
was compressed, but not to the same extent as the east-
ern block. Two depressions within the front of Block
A are illustrated, indicating zones of local extension
within the larger compressed zone. Ridges also indicate
main block to the west. The morphology of the failure
scar supports this interpretation -- the eastern portion of
the scar is rougher than the western area; the roughness
may have inhibited motion in the east until the west
block moved, providing kinematic freedom. S
UPERCHI
(2012) suggested that two main blocks were involved
in the 1963 event, consistent with our interpretation.
Field observations suggest a possible third block origi-
nating at the west corner of the failure surface. The fail-
ure scar here is bounded by a ridge at its west margin,
suggesting a bulldozing motion to the northwest. Stria-
tions on the failure scar that plunge toward the north-
west also indicate movement differing from the domi-
nant direction of movement. Tentatively, this could be
evidence of a block that separated from the main mass.
Conversely, the northwest movement could be due to
expansion of the material as it failed.
W
OLTER
et alii (in review) briefly discuss the 1963
slide deposit and the evolution of the failure scar. Our
morphogenetic maps complement and supplement
this work. The present failure scar consists of four el-
ements: exposed bedrock, vegetated areas, coarse de-
Fig. 7 - Compression and extension regions within the 1963 slide deposit, based on the distribution of ridges. Block B over-
rode Block A and is especially compressed. Slide directions are assumed to be perpendicular to ridge axes. The Mas-
salezza Gully remained intact within Block A during sliding. Inset shows the difference in size of some of the ridges in
Block B versus Block A, looking at the east margin of the slide from above Erto
background image
AN ENGINEERING GEOMORPHOLOGICAL CHARACTERISATION OF THE 1963 VAJONT SLIDE
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
621
by dilation or shearing through asperities, before cata-
strophic release was possible. The failure scar is a prime
example of this complex interaction. W
OLTER
et alii (in
review) produce a preliminary classification of failure
scar morphology based on a combination of photo-
grammetry, LiDAR, and field datasets, with classes
ranging from very smooth and planar to very rough and
crenulated. The rough areas of the failure scar, related
mainly to the interference between the two dominant
fold generations, likely inhibited movement, whereas
the smooth regions likely facilitated movement. Geo-
morphological processes have preconditioned the slope
for failure as well. Glaciers likely differentially eroded
the hinge of Erto Syncline and oversteepened the valley
walls. Rivers have incised the valley, locally creating
steep slopes prone to failure. Surficial mass wasting
has unloaded the slope, and several deep-seated fail-
ures have dramatically changed the topography and
dammed the Vajont River. Karst processes have eroded
carbonate bedrock and created pinnacles and dolines,
and karst networks may have allowed groundwater
transport to the failure surface from outside the surface
drainage basin. Precipitation has infiltrated rock mass-
es and locally elevated pore water pressures. Finally,
anthropogenic activity has further destabilised valley
walls, notably repeated filling and drawing down of the
Vajont Reservoir between 1960 and 1963. Combined,
the long- and short-term processes acting in the valley
have influenced the geomorphic stress path of the slope,
culminating in the catastrophic failure of 1963.
CONCLUSIONS
We interpreted the geomorphology of the 1963 Va-
jont Slide and the surrounding area using an engineer-
ing geomorphology approach. The morphological and
morphogenetic maps revealed several aspects of the
slide that support other research:
• a paleo-landslide is located in the same place as the
1963 failure,
• the 1963 slide consisted of two main blocks, with a
possible third at the west corner of the slide area,
• the failed blocks remained largely intact during the
slide, as shown by preservation of the Massalezza
Gully and pre-existing benches, and
• tectonics, geomorphology, and anthropogenic activity
interacted with one another, contributing to a time-
dependent reduction in the stability of the south slope
of Vajont Valley and ultimately to the 1963 failure.
directions of movement of different parts of the debris
mass. The east block likely moved to the NW. The ridg-
es in the west block are less consistent, but generally
suggest movement to the north. The west-central area
seems to have moved to the NW, which may show a
secondary failure rather than initial movements. S
UPER-
CHI
(2012) hypothesises similar movements using vec-
tors derived from pin points.
PRECONDITIONING FACTORS OF THE 1963
VAJONT SLIDE
The significance of the interaction between tecton-
ic and geomorphic, or endogenic and exogenic, proc-
esses to slopes has only recently been recognised. L
EITH
(2012) summarises this relationship within the context
of geomorphology, rock engineering, and slope insta-
bility and applies it to two valleys in the southern Swiss
Alps. The Vajont Slide also exemplifies the precondi-
tioning of slopes related to their tectonic and geomor-
phic histories. Both tectonic deformation episodes and
geomorphic processes have contributed to the cumula-
tive damage, or degradation, of the rock mass on the
north slope of Monte Toc. Faults have weakened the
rock mass and acted as release surfaces for the slide.
Two episodes of deformation produced folds that inter-
fered with one other, producing a complex topography
of basins and domes that had to be overcome, either
Fig. 8 - Evolution of the 1963 landslide scar. a) Map
of surficial materials on the failure scar in
2010/2011. b) Photograph of the Vajont Slide
area immediately after the 1963 failure. Note
that most of the slide scar is covered by debris,
especially on the west (photo: S
emenza
, 1964)
background image
A. WOLTER, D. STEAD, B.C. WARD & J.J. CLAGUE
622
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
ACKNOWLEDGEMENTS
We acknowledge contributions from our col-
leagues R. Genevois, M. Massironi, L. Superchi, and
L. Zorzi at the University of Padova, M. Ghirotti and
D. Donati at the University of Bologna and J. Griffiths
at University of Plymouth. LiDAR data were provided
by the Friuli-Venezia-Guilia Region. Research was
funded through a Natural Sciences and Engineering
Research Council of Canada (NSERC) Post-gradu-
ate Scholarship to A. Wolter and NSERC Discovery
Grants to D. Stead and J.J. Clague.
REFERENCES
B
roili
L. (1967) - New knowledges on the geomorphology of the Vaiont Slide slip surfaces. Felsmechanik und Ingenieurgeologie,
5 (1): 38-88.
C
Arloni
g.C. & M
AzzAnti
R. (1964a) - Rilevamento geologic della frana del Vaiont. Giornale di Geologia, 32: 105-138.
C
Arloni
g.C. & M
AzzAnti
R. (1964b) - Aspetti geomorfologici della frana del Vaiont. Rivista Geografica Italiana, 71: 201-231.
C
AStiglioni
B. (1940) - L’Italia nell’età quaternaria. Carta delle Alpi nel Glaciale (1:200 000 scale). In: d
Ainelli
g. (e
d
.).
Atlante Fisico-economico d’Italia. C.T.I., Milano. Tav. 3.
C
oppolA
L. & B
roMheAd
E.N. (2008) - Fossil landslide dams and their exploitation for hydropower in the Italian Dolomites.
Italian Journal of Geosciences, 127 (1): 163-171.
F
ookeS
p.g., l
ee
e.M. & g
riFFithS
J.S. (2007) - Engineering geomorphology: theory and practice. Whittles Publishing,
Caithness, Scotland, 281 pp.
F
ookeS
P.G., l
ee
E.M. & M
illigAn
G. (2005, e
dS
.) - Geomorphology for engineers. Whittles Publishing, Caithness, Scotland, 851 p.
g
eologiCAl
S
oCiety
in
l
ondon
(1982) - Working Party Report on land surface evaluation for engineering purposes. Quarterly
Journal of Engineering Geology, 15 (4): 265-328.
g
iArdino
J.r. & M
ArSten
R.A. (1999) - Engineering geomorphology: an overview of changing the face of earth. Geomorphology,
31: 1-11.
g
iudiCi
F. & S
eMenzA
e. (1960) - Studio geologic del serbatoio del Vajont. Report for Societa Adriatica di Elettricita (SADE).
Venice, Italy. 63 pp.
g
riFFithS
J.S., S
tokeS
M., S
teAd
D. & g
ileS
D. (2012) - Landscape evolution and engineering geology: results from IAEG
Commission 22. Bulletin of Engineering Geology and the Environment, 71: 605-636.
g
uerriCChio
A. & M
elidoro
g. (1986) - Geomorphological analysis of Vaiont Valley prior to the huge 1963 landslide. In: S
eMenzA
E.
& M
elidoro
g. (e
dS
.). Proceedings of the Meeting on the 1963 Vajont Landslide, Universita di Ferrara, Italy: 157-173.
h
endron
A.J. & p
Atton
F.D. (1985) - The Vaiont Slide: a geotechnical analysis based on new geologic observations of the failure
surface. US Army Corps of Engineers, Washington, DC, Technical Report GL-85-5, 324 pp.
l
eith
K.J. (2012) - Stress development and geomechanical controls on the geomorphic evolution of alpine valleys. PhD thesis,
ETH Zürich, Switzerland, 167 pp.
p
Aronuzzi
& B
ollA
A. (2012) - The prehistoric Vajont rockslide: An updated geological model. Geomorphology, 169-170 (1):
165-191.
r
oSSi
d. & S
eMenzA
E. (1964) - Relazione definitive sulle condizioni di stabilita della Costa delle Ortiche (Vaiont). Unpublished
report for Ente Nazionale per l’energia ELettrica (ENEL).
r
oSSi
d. & S
eMenzA
E. (1965) - Carte geologiche del versante settentrionale del M. Toc e zone limitrofe, prima e dopo il
fenomeno di scivolamento del 9 ottobre 1963, Scale 1:5000. Istituto di Geologia dell’Universita di Ferrara.
S
elli
r. & t
reviSAn
l. (1964) - Caratteri e interpretazione della frana del Vaiont. Giornale di Geologia, 32: 1-154.
S
eMenzA
E. (1967) - Sintesi degli studi geologici sulla frana del Vaiont dal 1959 al 1964. Museo Tridentino di Scienze Naturali,
Trento, Italy, 50 pp.
S
eMenzA
E. (2001) - La storia del Vajont, raccontata dal geologo che ha scoperto la frana. Tecomproject Editore Multimediale,
Ferrara, 280 pp.
S
uperChi
L. (2012) - The Vajont Rockslide: new techniques and traditional methods to re-evaluate the catastrophic event. PhD
thesis, Universita degli Studi di Padova, Italy, 187 pp.
Statistics