On October 15th, 2002 a rock volume of about 20000 mc fell into the Scascoli Gorge (25 km S of Bologna, Italy), damming the Savena River and destroying a 150 m long segment of the adjacent road (see part 2). The intrinsic predisposition to slope instability of the Scascoli Gorge is related to a complex interplay of stratigraphic, tectonic and geomorphic features. The local stratigraphic succession is composed of Upper Oligocene sandstones, Lower Miocene cherty marls, Middle Miocene calcareous sandstones and Lower Pliocene conglomerates. The local tectonic setting is represented by a NW-dipping monocline offset by two families of normal faults. The main geomorphic character of the Gorge is its asymmetrical profile, composed of a nearly vertical left slope, and a less steep right slope. This profile was carved during a progressive NW-ward drift of the riverbed, controlled by three factors: (1) overall NW-ward dip of bedding planes; (2) ancient river obstruction by a 20000000 mc landslide detached from the SE valley-side (the "Scascoli landslide"); (3) recent roadbed building on the SE riverbank. Slope undermining due to the riverbed drift is the most important preparatory cause of rock falls (topples) from the NW valley-side. Other predisposition factors control active land sliding from the SE valley-side, where two different kinds of movement can be envisaged: (1) rock falls (slides) from fractured and weathered beds dipping down slope; (2) earth and debris slumps triggered by local reactivations of the dormant Scascoli landslide. The first situation occurs in the northern third of the Scascoli Gorge, where it represents quite an obvious hazard for the road underneath. The second situation is typical of the southern two thirds of the Gorge, where the Scascoli landslide foot was dissected by river erosion. The distinctive geologic and geomorphic features of this centuries-old, dormant landslide are here reported on detail maps and DEM morphometric elaborations, also shown in 3D interactive format, which support its classification as a multiple roto-translational rockslide. Accurate cross-sections, calibrated by seismic tomography and drilling cores, place the sliding surface in the basal part of the cherty marls unit, rich in clay and tephra layers. Inclinometric readings and topographic monitoring concurrently show that the landslide foot is actively sliding on the same surface (differential vertical displacements from one to eight millimetres/year).
LANDUZZI A., BENEDETTI G., GUALDRINI M., FERRO S., MARCHI G. (2004). LANDSLIDES IN THE SCASCOLI GORGE (BOLOGNA APENNINES, ITALY): FROM RECONNAISSANCE TO MONITORING (PART 1). FLORENCE : s.n.
LANDSLIDES IN THE SCASCOLI GORGE (BOLOGNA APENNINES, ITALY): FROM RECONNAISSANCE TO MONITORING (PART 1)
LANDUZZI, ALBERTO;MARCHI, GIANFRANCO
2004
Abstract
On October 15th, 2002 a rock volume of about 20000 mc fell into the Scascoli Gorge (25 km S of Bologna, Italy), damming the Savena River and destroying a 150 m long segment of the adjacent road (see part 2). The intrinsic predisposition to slope instability of the Scascoli Gorge is related to a complex interplay of stratigraphic, tectonic and geomorphic features. The local stratigraphic succession is composed of Upper Oligocene sandstones, Lower Miocene cherty marls, Middle Miocene calcareous sandstones and Lower Pliocene conglomerates. The local tectonic setting is represented by a NW-dipping monocline offset by two families of normal faults. The main geomorphic character of the Gorge is its asymmetrical profile, composed of a nearly vertical left slope, and a less steep right slope. This profile was carved during a progressive NW-ward drift of the riverbed, controlled by three factors: (1) overall NW-ward dip of bedding planes; (2) ancient river obstruction by a 20000000 mc landslide detached from the SE valley-side (the "Scascoli landslide"); (3) recent roadbed building on the SE riverbank. Slope undermining due to the riverbed drift is the most important preparatory cause of rock falls (topples) from the NW valley-side. Other predisposition factors control active land sliding from the SE valley-side, where two different kinds of movement can be envisaged: (1) rock falls (slides) from fractured and weathered beds dipping down slope; (2) earth and debris slumps triggered by local reactivations of the dormant Scascoli landslide. The first situation occurs in the northern third of the Scascoli Gorge, where it represents quite an obvious hazard for the road underneath. The second situation is typical of the southern two thirds of the Gorge, where the Scascoli landslide foot was dissected by river erosion. The distinctive geologic and geomorphic features of this centuries-old, dormant landslide are here reported on detail maps and DEM morphometric elaborations, also shown in 3D interactive format, which support its classification as a multiple roto-translational rockslide. Accurate cross-sections, calibrated by seismic tomography and drilling cores, place the sliding surface in the basal part of the cherty marls unit, rich in clay and tephra layers. Inclinometric readings and topographic monitoring concurrently show that the landslide foot is actively sliding on the same surface (differential vertical displacements from one to eight millimetres/year).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
