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Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
459
DOI: 10.4408/IJEGE.2013-06.B-44
LANDSLIDES AND INFRASTRUCTURES:
THE CASE OF THE MONTAGUTO EARTH FLOW IN SOUTHERN ITALY
L
uigi
GUERRIERO
(*)
, P
aoLa
REVELLINO
(*)
, g
erardo
GRELLE
(*)
,
F
rancesco
FIORILLO
(*)
& F
rancesco
M. GUADAGNO
(*)
(*)
University of Sannio - Department of Sciences and Technologies - 82100, Benevento, Italy
slides; 2) more than 480,000 landslide-events have
been recognized in the Italian territory affecting a total
area of 20,721 km
2
; 3) approximately 1 million people
are exposed to landslide hazard.
By the IFFI project’s estimates, the railway and
highway networks have been involved or could be po-
tentially involved in more than 1800 sites and 700 sites
respectively by active landslides. Most of the landslides
involving highways and railways were triggered by ex-
treme or time-prolonged rainfall events (e.g. d
iodato
,
2006). Moreover, most of the Italian transport network
is located in high seismic hazard areas. Thus, we have
to expect potential reactivation of quiescent landslides
connected to seismic activity (e.g. g
reLLe
et alii, 2011).
This paper aims at describing the effects on infra-
structures related to the temporal and spatial evolution
of one of the most important recent landslides in South-
ern Italy: the Montaguto earth flow (Fig. 1). In addition,
analysis of data from the Orsara di Puglia meteorologi-
cal station has been carried out in order to detect the
relationship between landslide activity and rainfall. The
landslide was not listed into the AVI project catalogue
(g
uzzetti
et alii, 1994) preventing a correct risk analy-
sis of potentially involved areas and infrastructures.
GEOLOGICAL AND HYDROGEOLO-
GICAL SETTING OF THE LANDSLIDE
AREA
The Montaguto earth flow (Fig. 1) is located in
the southern Daunia Mountains on the south-facing
ABSTRACT
The Montaguto earth flow is one of the most recent
landslides involving infrastructure in Southern Italy. It
has been periodically active during the last 70 years.
This paper provides a description of the main phases
in the earth flow activity and its effects on an important
Italian national road and railroad tract. The most impor-
tant earth flow reactivations occurred in 2006 and 2010,
when the “SS-90” National Road and the “Benevento-
Foggia” tract of the National Railroad, which both con-
nect the east coast to the west coast, were destroyed by
the landslide. A preliminary analysis of rainfall data
showed that the most important earth flow reactivations
occurred after at least two wet hydrological years.
K
ey
words
: Earth flow, Infrastructure, Italy, Montaguto, lan-
dslide, kinematic
INTRODUCTION
The interaction of landslides with human linear in-
frastructures is often the cause of disasters (e.g. g
eert
-
seMa
et alii, 2009). In industrialized countries landslides
cause billions of Euro in damage every year. In Italy land-
slide impact on roads, railways and buildings cause mil-
lions of Euro per year in damage and restoration as well.
Data from the Italian Landslide Inventory (IFFI
project - www.sinanet.apat.it/progettoiffi/), regarding
landslide spatial-distribution within the Italian terri-
tory from 1116 to 2007, show that: 1) more than 70%
of Italian municipalities have been affected by land-
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L. GUERRIERO, P. REVELLINO, G. GRELLE, F. FIORILLO & F.M GUADAGNO
460
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
the same period and farther downslope along the east-
ern flank of the landslide, the water flow from a differ-
ent group of springs that feed the so-called Rane lake
was also approximately 2.0 l/s.
THE MONTAGUTO EARTH FLOW: MAIN
PHASES AND ACTIVITY
EARTH FLOW DESCRIPTION
The Montaguto earth flow is located within the
Cervaro River valley at about 4566000 N and 518000
E UTM (Fig. 3). Throughout this paper, the term earth
flow is used when describing the Montaguto landslide
because it is composed of predominantly fine-grained
material and it has a flow-like surface morphology
(V
arnes
, 1978; K
eeFer
& J
ohnson
, 1983; h
ungr
et
alii, 2001). However, most of the movement takes
place by sliding along discrete shear surface.
The landslide is 3 km long covering an area of
about 67 ha and involving about 6 millions of m
3
. The
earth-flow width ranges from 75 m at the earth-flow
neck (see below) to 450 m in the upper part of the
earth-flow source area. The total elevation difference,
from the toe next to the Cervaro River to the top of
the 90 m high headscarp, is approximately 440 m. The
average slope angle, excluding the headscarp, is ap-
proximately 7.2°.
The earth flow source area is about 900 m long
and is formed by two coalescent source zones. The
eastern zone has developed in a NE-SW direction, has
a hopper shape and covers an area of 20 ha. The west-
ern zone has developed in a N-S direction and covers
an area of 4 ha. In this area, the earth-flow movement
is controlled by the bedding of the Flysch of Faeto
formation. The bedding strike is about N40°E, dip-
ping as does the hillslope and the eastern part of the
source area fails with an oblique motion along the
bedding planes. The terrains are very fractured, and
many springs flow from these fractures, at elevations
between 750-800 m a.s.l., to the landslide body.
The lower end of the source area is the narrow-
est part of the landslide, herein called the neck. The
landslide neck is located in a structural depression cre-
ated by the intersection of a syncline fold with NW-SE
trending normal faults (Fig. 2).
Downhill from the neck, the landslide is located
along the eastern flank of a NW-SE trending syncline
and moves along a bedrock surface roughly parallel to
the axis of the syncline. From 500 m a.s.l. to the base
side of La Montagna Mt. The geology in this part of
the Apennine Chain is tectonically complex and large-
scale structures and deformed bedding often control
the geometry and behavior of landslides (e.g. F
ioriLLo
,
2004; r
eVeLLino
et alii, 2010; g
reLLe
et alii, 2011).
In the earth-flow area, the Flysch of Faeto forma-
tion (Pescatore et al., 1996) and the Villamaina Unit
(P
escatore
et alii, 1996) outcrop (Fig. 2). The Flysch
of Faeto formation can be widely recognized in the
upper part of the valleyside, from 650 m a.s.l. to the
top; whereas the Villamaina Unit, it crops out in the
middle and lower part. The contact between the two
formations is unconformity (Pescatore et al., 1996).
The structural deformation of the terrains in the
landslide area resulting from Miocene and Pliocene
tectonics is very complex (P
escatore
, 1978, P
atacca
& s
candone
, 1989). Fold and fault systems have been
recognized with two predominant trends (NW-SE
and NE-SW), leading the landslide source area to be
located within a synclinal fold structure with an axis
characterized by a NE-SW orientation.
The resulting hydrogeological setting also is
very complex due to the geology of the area. Several
springs are emerging in and nearby the landslide area
from about 600 to 800 m a.s.l. The Flysch of Faeto
formation, outcropping at the higher elevations, is
highly fractured and therefore highly permeable. Lo-
cations of springs are typically controlled by a local
permeability contrast between clayey and fractured
strata. Many springs are placed in the upper part of
the source area, near the main scarp, and upslope on
the eastern flank of the landslide at approximately 600
m a.s.l. . In May 2010, the flow of water from all the
springs of the source area was estimated at 2.0 l/s. In
Fig . 1 - Oblique view from a helicopter of the the Mon-
taguto earth flow on 27 April 2006 looking south
toward the earth-flow toe
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LANDSLIDES AND INFRASTRUCTURES: THE CASE OF THE MONTAGUTO EARTH FLOW IN SOUTHERN ITALY
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
461
From 2006 to 2010, earth flow features were
mapped using kinematic GPS techniques, with a hori-
zontal accuracy of about ±1 m, onto a shaded relief
base map. Shaded-relief maps were created from
available LiDAR data using DEM Relief Shader 2.3
QGIS-Plugin (Andreas Plesch, plugin for OSGeo pub-
lic domain software, http://www.qgis.org/ ).
Older mapping was obtained from both aerial
photo and orthophoto interpretations (according to
K
eaton
& d
egraFF
, 1996). We collected stereo pairs
of 1954, 1976, 1985, 1991, 2003 and an orthophoto
of 2005. For periods when stereo-aerial photos were
available, landslide features were mapped using a
stereoscope. Manually mapped features were trans-
ferred to rectified photo base maps created from aerial
photos scanned at 625 dpi (4 micron pixels). Photos
were rectified using between 30 and 50 Ground Con-
trol Points (GCPs). These GCPs, which were visible
in both the historical photos and in the field (e.g.
of the hillslope, the landslide occupies a v-shaped val-
ley, therefore only the upper part of the flanks of the
valley are recognizable.
EARTH FLOW EVOLUTION
Multi-temporal analysis of the Montaguto earth
flow was carried out in order to investigate earth flow
modification and activity from 1954 to 2010.
Fig . 3 Location of the Montaguto earth flow (in black)
within the Cervaro-River valley. Surrounding
town and drainage pattern are also shown
Fig. 2 - Geological map of the Montaguto earth flow.
Legend: d, colluvial deposits; a, alluvial de-
posits; FV, Villamaina Unit; FF, Flysh of Fa-
eto formation; line with hachures, normal fault;
line with triangles, axis of fold structure. The
hachured line indicates buried structures. The
white area with the contour line indicates the
earth-flow area. Coordinates in UTM 33 N are
shown
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L. GUERRIERO, P. REVELLINO, G. GRELLE, F. FIORILLO & F.M GUADAGNO
462
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
ed by an irregular-shaped headscarp. Many single
shallow landslides were active within the source
area. The earth-flow neck was well defined, reaching
about 45m in width. As the earth flow emerged from
the earth-flow neck, it changed direction and moved
southeast, instead of southwest. The older earth flow
deposit present to the southwest of the neck in 1954
showed an enlargement of up to approximately 11 ha,
but it was inactive in 1976. The active earth-flow toe
reached an elevation of approximately 550 m a.s.l.
and had a large pond (locally called “Lago delle
Rane” see Fig. 4b) on its surface. The earth-flow
creek, which flowed southeast in 1954, now flowed
southwest , and it was recognized along the whole
length of the earth flow.
From 1985 to 2005 the overall shape of the earth
flow did not change significantly. The earth-flow neck
had the same configuration until 2003. In 2005 it was
several meters wider than in 2003 and many ponds
were present within the earth flow.
In 2006 (Fig. 5a) the extent and the shape of the
earth flow was notably different in comparison to that
of 2005. The source area appeared to have complex
boundary geometries with multiple smaller source
corners of buildings, centers of stationary trees, etc.)
were surveyed using real-time kinematic Global Po-
sitioning System (GPS) techniques (e.g. g
iLi
et alii,
2000) with dual-frequency GPS receivers in April
2010 (g
uerriero
et alii, 2013).
A description of the most important periods in
earth flow evolution is provided below analyzing the
earth flow features.
Since 1954, earth-flow movement alternates be-
tween long periods of relatively slow movement and
relatively rapid surges, as in 2006 and 2010. The time
span from 2006 to 2010 can be considered as one of
the most intense active period.
In 1954 (Fig. 4a), the earth flow was about 1 km
long covering an area of about 15 ha. The source
area was branched in several coalescent scar zones.
The landside toe formed two different accumulation-
areas. The younger deposit, which covered a surface
of about 4000 m
2
, had a fan shape and overrode the
older deposit that extended for an area of approxi-
mately 3.5 ha.
In 1976 (Fig. 4b), the earth flow was larger and
more complex than in 1954, measuring approximate-
ly 2 km long. The source area had expanded, bound-
Fig. 4 - Maps of the Montaguto earth flow in 1954 (a) and
1976 (b)
Fig. 5 - Maps of the Montaguto earth flow in 2006 (a) and
2010 (b)
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LANDSLIDES AND INFRASTRUCTURES: THE CASE OF THE MONTAGUTO EARTH FLOW IN SOUTHERN ITALY
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
463
analysis because the series is the longest and the most
continuous for this area.
Wet hydrological years occur when the cumula-
tive rainfall in the hydrological year exceed the av-
erage values of the series of one standard deviation
(μ+σ). Dry hydrological years occur when the cumu-
lative rainfall in the hydrological year is below the
series average of the one standard deviation (μ-σ).
Based on this criterion, wet and dry years are observ-
able in the graph in Fig. 6.
Dry years with rainfall below average, especially
if consecutive, determine conditions that could in-
hibit landslide reactivation. For this reason the long
period from 1986-87 to 2001-02 was a period of
stability for the Montaguto earth flow. This long dry
period was broken by 3 consecutive wet years: 2002-
03, 2003-04, 2004-05. The hydrological year 2005-
06 was exceptional in terms of amount of rain and
in April 2006 the Montaguto earth flow remobilized,
involving the SS90 National Road. Other wet years
in the past that were characterized by an amount of
rain higher than 2005-06 are: 1975-76, 1957-58 and
1933-34. It is important to note that only the years
1975-76 and 1957-58 followed a precedent wet year.
Historical data, regarding earth flow activity, reports
that the earth flow was active in 1958 (g
uerriero
et
alii, 2013).
In order to highlight the trend of rainfall during
each hydrological year and correlate it to the landslide
activity, Fig. 7 shows the cumulative rainfall of all wet
hydrological years when the series average is exceeded
by one standard deviation in March or April. In particu-
lar in 2005-06 the rainfall amount exceeded the average
of one standard deviation around March 15
th
. About a
month later, the Montaguto earth flow remobilized.
It is important to note the absence of 1975-76. It
was characterized by heavy rainfall, but only in the
months of June and July.
zones, which may have been controlled by bedding
(r
eVeLLino
et alii, 2010; g
reLLe
et alii, 2011). Within
the earth-flow body, the ponds visible in 2005 (exclud-
ing Lago delle Rane) remained in the same positions
as those of 2005, but decreased in size. Lago delle
Rane moved approximately 60 m to the east from
its position in 2005. It became larger and separated
from the main earth flow by strike-slip shear struc-
tures. From this point downslope, the v-shaped drain-
age valley was filled by earth-flow material from the
April 2006 remobilization. The new earth-flow toe
was placed on the National Road, SS90, and had a fan
shape indicative of lateral expansion.
From 2007 to 2009 the overall shape of the earth
flow remained very similar to that of 2006, even
though the landslide was actively moving in this time
period, above all on the lower part of the earth-flow
toe. The peak of velocity at the toe was observed by
the authors during the night between the 5th and the
6
th
June 2009. The upper part of the earth flow toe in-
creased its velocity reaching 4.5 m/h. Hydrologic fea-
tures along the whole earth flow did not change.
On March 3
rd
2010 (Fig. 5b) the earth flow toe
expanded involving both the SS 90 National road and
the Benevento-Foggia National railway.
RAINFALL AND LANDSLIDE ACTIVITY
The possibility of identifying a relationship be-
tween rainfall and reactivations of the landslide is
investigated in this paper, through a simple statistical-
empirical approach. We analyzed rainfall records of
the “Orsara di Puglia” Meteorological station com-
piled for the hydrological year (September-August)
from 1921-22 to 2008-2009.
The Orsara di Puglia Meteorological station is lo-
cated about 5.5 km NE of the Montaguto earth flow at
approximately 650 m a.s.l..
We used monthly data from this station for our
Fig. 6 - Annual rainfall historical series (Orsara di Puglia rain gauge, 650 m a.s.l.); μ and σ are the mean and deviation
standards, respectively
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L. GUERRIERO, P. REVELLINO, G. GRELLE, F. FIORILLO & F.M GUADAGNO
464
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
MAIN INTERACTIONS WITH INFRAC-
STUCTURES
As stated above, the Montaguto earth flow has
been periodically active since at least 1954 (g
uer
-
riero
et alii, 2013) and the most important phases in
terms of effect and impact on infrastructures corre-
spond to the reactivations of 2006 and 2010.
On April 26
th
2006, for the first time, the earth flow
cut the east-west trending Italian national road (Fig.
8), which connects the east- and west-coast provinces
of Foggia and Avellino, damaging some buildings, and
stopped at approximately 30 m from the Benevento-
Foggia national railroad. This mobilization is the largest
and the most rapid documented in the last 70 years with
a movement of about 6 million cubic meters of landslide
material and observed velocities reaching 1 m/hour.
The National road was completely covered by the
landslide for a length of approximately 250 m. This
event produced the filling of the V-shape valley de-
veloped from 550 m a.s.l. Here the landslide material
reached the maximum thickness of 25 m near the axis
of the creek. The magnitude (volume) of this earth
flow event has significant precedents in southern Italy,
such as the Covatta landslide, which occurred in 1996
Fig. 8 - The Montaguto earth flow on 27
th
April 2006
Fig. 9 - The Montaguto earth flow on 3
rd
April 2010
Fig. 7 - Trend of cumulative rainfall for some major wet years (coloured curves). The black dashed curves, from the bottom
upwards, represent the average cumulative rainfall from September, the average plus one standard deviation, and
the average plus two standard deviation, respectively. The activation of the landslide occurred in April 2006 after a
rainfall event that is at least one standard deviation of the historical average
background image
LANDSLIDES AND INFRASTRUCTURES: THE CASE OF THE MONTAGUTO EARTH FLOW IN SOUTHERN ITALY
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
465
represent a continuing risk when they involve towns
or linear infrastructures, such as roads and railroads.
This paper has provided an excursus on the main
phases and activity of the Montaguto earth flow describ-
ing its interactions with important linear infrastructures.
Both the SS 90 delle Puglie National Road and the Be-
nevento-Foggia national Railroad were involved in the
earth flows in 2006 and 2010, respectively. The analysis
of rainfall data indicates that the most important reac-
tivation of the Montaguto earth flow occurred after at
least two wet hydrological years, although we have no
data regarding the 2010 event. Before 2006, the Mon-
taguto earth flow had been almost inactive for several
decades. Historical data and climatic indications sug-
gest that in 1958 the Montaguto earth flow had been
active. After the long period of rough stability, a fast
evolution and reactivation were unexpected. The lesson
learnt from the Montaguto landslide, which was not in-
ventoried in national landslide catalogs, highlights the
need for new regional re-analyses along the main hu-
man linear infrastructures at least. Therefore, studies of
landslide hazard and risk assessments need to consider
not only the actual interaction between slope evolution
and linear infrastructures but also future evolutions
under possible different climatic conditions. More re-
search should be done to assess likely future hazards
and to predict slope behavior also under risk scenarios
of changing climate.
involving the SS 647 National road and damming the
Biferno River (c
orbi
et alii, 1999) or the Ruderi land-
slide in Basilicata region (d
eL
P
rete
et alii, 1977). It
was a clear hazard for infrastructure and had critical
risk implications for Italian national transportation.
The 2010 event (Fig. 9) was similar to that of 2006
involving part of the earth flow toe. The volume mo-
bilized was more than 300,000 m
3
and the velocity of
movement was up to 0.5 m/h. The landslide material
reached and covered the railroad Benevento-Foggia.
Immediately after the reactivation, the thickness of ma-
terial on the railway was about 4 m. The removal of ma-
terial lasted some months and at the beginning of July
the railway and the national road were reopened. This
event represents the peak of several weeks of activity
of the earth flow at M
ontaguto
in early 2010. Before
covering the railroad, the earth flow had already caused
several closures of the SS 90 national road.
CONCLUDING REMARKS
Landslides are one of the most important natural
hazards in Italy in terms of spatial and temporal dis-
tribution. Morphological evolution is linked to active
landslide processes affecting a large part of the central-
southern Apennine. Slow-velocity landslides predomi-
nate in wide areas, due to the prevalent clayey nature
of the outcropping deposits. If these landslides have
to be considered as a low risk for human life, they can
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Statistics