Gravitational Slope Deformation Research Articles

Quaternary gravitational morpho-genesis of Central Apennines (Italy): Insights from the Mt. Genzana case history

Abstract This paper focuses on a study aimed at defining the role of geological-structural setting and Quaternary morpho-structural evolution on the onset and development of a deep-seated gravitational slope deformation which affects the western slope of Mt. Genzana ridge (Central Apennines, Italy). This case history is particularly significant as it comprises several aspects of such gravitational processes both in general terms and with particular reference to the Apennines. In fact: i) the morpho-structural setting is representative of widespread conditions in Central Apennines; ii) the deforming slope partially evolved in a large rockslide-avalanche; iii) the deformational process provides evidence of an ongoing state of activity; iv) the rockslide-avalanche debris formed a stable natural dam, thus implying significant variations in the morphologic, hydraulic and hydrogeological setting; v) the gravitational deformation as well as the rockslide-avalanche reveal a strong structural control. The main study activities were addressed to define a detailed geological model of the gravity-driven process, by means of geological, structural, geomorphological and geomechanical surveys. As a result, a robust hypothesis about the kinematics of the process was possible, with particular reference to the identification of geological-structural constraints. The process, in fact, involves a specific section of the slope exactly where a dextral transtensional structure is present, thus implying local structural conditions that favor sliding processes: the rock mass is intensively jointed by high angle discontinuity sets and the bedding attitude is quite parallel to the slope angle. Within this frame the gravitational process can be classified as a structurally constrained translational slide, locally evolved into a rockslide-avalanche. The activation of such a deformation can be in its turn related to the Quaternary morphological evolution of the area, which was affected by a significant topographic stress increase, testified by stratigraphic and morphologic evidence.

The Gradenbach Observatory—monitoring deep-seated gravitational slope deformation by geodetic, hydrological, and seismological methods

The Gradenbach mass movement (GMM) is an example of DGSD (deep-seated gravitational slope deformation) in crystalline rocks of the Eastern Alps (12.85°E, 47.00°N). The main body of the GMM covers an area of 1.7 km2 and its volume is about 120 × 106 m3. A reconstruction of the deformation history yields a mean displacement of ∼ 22 m from 1962 to 2011. In 1965/66, 1975, 2001, and 2009 high sliding velocities, exceeding several meters per year, interrupt the quasi-stationary periods of slow movement (≤0.3 m/year). Since 1999 the displacement of the main body of the GMM has been observed by GPS. Time series of extensometer readings, precipitation, snow cover water equivalent, water discharge, and hydrostatic water level observed in boreholes were re-processed and are presented in this paper. Continuous recording of seismic activity by a seismic monitoring network at the GMM began in the summer of 2006. Deformation has been monitored since 2007 by an embedded strain rosette based on fiber optics technology and a local conventional geodetic deformation network. The velocity of the GMM could be modeled to a large extent by a quantitative relation to hydro-meteorological data. During the phase of high sliding velocity in spring 2009, the seismic activity in the area increased significantly. Several types of seismic events were identified with some of them preceding the acceleration of the main body by about 6 weeks. The potential inherent in the Gradenbach Observatory data to supply early warning and hazard estimation is discussed.

Influence of deep-seated gravitational slope deformations on landslide distributions: A statistical approach

The influence of deep-seated gravitational slope deformations (DSGSDs) on the distribution of translational landslides was analyzed in the Milia basin, Tuscany, Italy. Detailed geomorphological mapping, combined with the analysis of aerial photography, enabled us to build two landslide inventories. One inventory including landslides before 1975 was used to create statistical models, whereas the other inventory including landslides after 1975 was used to validate the models. Geology, slope angle, slope aspect, distance to hydrographic elements, and distance to tectonic lineaments were considered as landslide-predisposing factors. To quantify the importance of DSGSDs as another landslide-predisposing factor, the DSGSD presence/absence map was introduced in the stepwise statistical analysis. The landslide inventory maps and factor maps were processed using a conditional analysis on all possible factor combinations to produce landslide susceptibility maps with five susceptibility classes. The results indicate that the DSGSDs significantly affect landslide distribution.

Deep seated gravitational slope deformations in the European Alps

Abstract Deep seated gravitational slope deformations (DSGSD) are widespread phenomena, recognized in different mountain ranges worldwide. The distribution of such phenomena at the scale of a mountain belt has rarely been systematically analysed in the past. Aim of the paper is to present and discuss an inventory map of DSGSD at the scale of the entire European Alps, in order to review existing knowledge and investigate general controls on these phenomena. The criteria adopted for their classification and distinction are presented. A total of 1033 DSGSDs, ranging in size between 0.03 and 108 km 2 , have been mapped. The inventory has been validated against available local or regional landslide inventories at different scales and prepared by different authors using different approaches. The frequency–area relationship for the mapped features is presented. The spatial distribution of the mapped DSGSD has been quantified by discretizing the study area into regular square grids with different resolution, and analysed with respect to a variety of geological, geomorpohological and morphometric variables, and of their clustering. Discriminant, principal component and cluster analyses have been performed to define the most important controlling and predisposing factors. Results suggest that the occurrence of foliated metamorphic rocks, LGM ice thickness, local relief (and related parameters), slope size, drainage density and river stream power are the local parameters most positively correlated to DSGSD occurrence. The impact of these phenomena on slope morphology, in terms of hypsometry and slope gradient adjustment is also discussed.

Development of deep-seated gravitational slope deformation on a shale dip-slope: Observations from high-quality drill cores

Abstract We analyzed high-quality drill cores with 100% recovery drilled into a gravitationally deformed dip-slope of a shale-dominated sequence of sediments in Japan. The slope had undulating surfaces but no well-defined landslide scarps, suggesting that parts of the slope had undergone gravitational deformation but had not completely separated from the surrounding bedrock. The gravitational deformation of shale and sandstone is characterized by disintegration and brecciation of sediments and the formation of pulverized zones with poorly developed planar structures, jigsaw-like structures, and fracture openings. Shear zones are distributed intermittently within the slope but have not merged discernably into a through-going master sliding surface. Incipient landslide shear zones form openings within coherent rock by shearing along bedding, with these shear zones potentially developing downward in a stepwise manner, which may be related to stress redistribution induced by river incision.

Deep-seated gravitational slope deformations as possible suitable locations for prehistoric human settlements: An example from the Italian Western Alps

The Plan di Modzon is a mountain area (2300 m) located in the Verrogne Valley, NW of Aosta (Western Alps). It occurs along the contact between the Middle Penninic (micaschist and gneiss from the Gran San Bernardo Nappe) and the overlying upper units of the Piedmont Zone (carbonate calcschist alternating with marble).This area, largely shaped by Pleistocene glaciers, was involved in a wide deep-seated gravitational slope deformation (Pointe Leysser DSGSD) on the western extension of the Becca France doubled ridges. Several ridges that were affected by glacial erosion, discontinuously covered by glacial sediments, are present throughout the area. Extremely fractured rocks and various gravitational forms (minor scarps and trenches) mark the DSGSD.Several archaeological sites (MF1–MF9) have recently been found between 2242 and 2292 m asl. They have revealed artifacts of rock crystal (hyaline quartz) referred to the Sauveterrian stage of the Mesolithic. An ensemble of other archaeological evidence is referred to the Copper Age. The investigation in progress specifically concerns the systematic excavation of sites MF1 and MF3.Some concomitant morphological factors have created very favorable conditions for prehistoric settlements in the Plan di Modzon area, including the exceptionally wide valley floor directly perched on the main Dora Baltea Valley, in consequence of the Verrogne Glacier diversion promoted by the P. Leysser DSGSD. Easy and direct accessibility to this area is provided by the gently-dipping slope of the Dora Baltea Valley affected by the DSGSD. The ridged and grooved morphology as the result of the glacial and gravitational interaction, offered wide surfaces free from geological hazards (debris flow and avalanche processes). The DSGSD is, therefore, one of the primary causes of the archaeological settlement of this area, contributing to create a morphology adapted to prehistoric settlements.

Giant non-catastrophic landslides and the long-term exhumation of the European Alps

Landslides influence local slope morphology, affect sediment flux from hillslopes to rivers, and mass wasting in response to tectonics and climate forcing. However, the links between giant, non-catastrophic landslides known as Deep-Seated Gravitational Slope Deformations (DSGSDs) and the long-term evolution of orogenic landscapes are almost unknown. We explore these links in the European Alps using the first orogen-scale inventory of DSGSDs (>900 over an area >105km2) and a dataset of published apatite fission-track ages (>1000) that provides an estimate of the long-term exhumation patterns of the orogen. We show that DSGSDs are more widespread than previously considered, and exhibit an orogen-scale distribution not explained by well-known local lithological and structural controls. We test the hypothesis that this orogen-scale distribution correlates to the long-term evolution of the Alps by subdividing the study area into 37 square sub-areas (50×50km), classified according to combinations of long-term exhumation and mean annual rainfall. On each sub-area we perform a morphometric analysis of topography (hypsometry, relief, slope). Excluding local and regional controls due to rock type and structure, DSGSDs tend to cluster in areas with intermediate exhumation rates (fission-track age between 10 and 40Ma), where large-scale topography is less dissected and incision is localised along major valleys. Here DSGSD abundance correlates positively with the degree of valley incision and related relief. Instead, DSGSDs lack in areas which underwent either low exhumation rates, resulting in insufficient relief production, or high exhumation rates associated to rapid uplift or higher erosional dissection of topography. Negative correlation between DSGSD abundance and mean annual rainfall suggests that effective hydrological surface processes contribute, on the long-term timescale, to the development of large-scale topography unfavourable to DSGSDs, especially in areas of high exhumation rates. Where DSGSDs are abundant, long-lasting slope deformations effectively adjust post-glacial relief by reducing slope inclination values, and are thus expected to significantly contribute to the long-term denudation of active orogens.

Spatial pattern of landslides in Swiss Rhone Valley

The present study analyses the spatial pattern of quaternary gravitational slope deformations (GSD) and historical/present-day instabilities (HPI) inventoried in the Swiss Rhone Valley. The main objective is to test if these events are clustered (spatial attraction) or randomly distributed (spatial independency). Moreover, analogies with the cluster behaviour of earthquakes inventoried in the same area were examined. The Ripley’s K-function was applied to measure and test for randomness. This indicator allows describing the spatial pattern of a point process at increasing distance values. To account for the non-constant intensity of the geological phenomena, a modification of the K-function for inhomogeneous point processes was adopted. The specific goal is to explore the spatial attraction (i.e. cluster behaviour) among landslide events and between gravitational slope deformations and earthquakes. To discover if the two classes of instabilities (GSD and HPI) are spatially independently distributed, the cross K-function was computed. The results show that all the geological events under study are spatially clustered at a well-defined distance range. GSD and HPI show a similar pattern distribution with clusters in the range 0.75–9 km. The cross K-function reveals an attraction between the two classes of instabilities in the range 0–4 km confirming that HPI are more prone to occur within large-scale slope deformations. The K-function computed for GSD and earthquakes indicates that both present a cluster tendency in the range 0–10 km, suggesting that earthquakes could represent a potential predisposing factor which could influence the GSD distribution.

Timing and periodicity of paraglacial rock-slope failures in the Scottish Highlands

Many formerly-glaciated mountains exhibit a high density of postglacial rock-slope failures (RSFs) in the form of rockslides, rock avalanches or deep-seated gravitational slope deformations. Such RSFs are often termed ‘paraglacial’ as they reflect pre-conditioning by glaciation and deglaciation. The temporal pattern of paraglacial RSFs is unknown. We employ 47 cosmogenic isotope exposure ages obtained for 17 catastrophic RSFs in the Scottish Highlands to test models of changes in RSF frequency since deglaciation. Our results show that RSF activity spans almost the entire postglacial period from ~17ka until ~1.5ka, and that the periodicity of sampled postglacial RSFs is statistically indistinguishable from a pattern of uniform periodicity (~1ka−1). Our data do not conform to proposed models of declining RSF frequency with time elapsed since deglaciation, but suggest that the temporal distribution of postglacial RSFs is best described by a combination of rapid response (enhanced RSF frequency during or immediately after deglaciation) followed by approximately constant periodicity. Our findings are consistent with near-surface fracturing of rock when glacially-induced confining stresses are removed, causing some failures during or immediately after deglaciation and reducing other slopes to critical conditional stability so that failure is triggered by progressive rock-mass weakening or by transient triggering mechanisms. Neither permafrost degradation (thaw of ice in joints) nor seismic activity offers a general explanation for triggering Scottish RSFs, but could be contributory in some cases. The quasi-constant periodicity inferred for Holocene RSFs implies that the probability of RSFs in this seismically-quiescent intraplate area has not changed in the past ~10ka, and that further (though infrequent) catastrophic RSFs are likely to occur in the future.

Application of infrared thermography for mapping open fractures in deep-seated rockslides and unstable cliffs

We present a new approach for mapping open cracks and tension fractures within rock slope instabilities and rock cliffs, which resides in high-resolution ground-based and airborne infrared thermography (IRT). The method is restricted to cold seasons, and its utility is demonstrated through three examples from the Flysch Belt of the Outer West Carpathians (rockslides at Kopce Hill and Mt. Kněhyně) and from the Northern Calcareous Alps (deep-seated gravitational slope deformations in Gschliefgraben/Mt. Traunstein). The approach is based on a contrast between temperatures deep within the rock mass, which at a depth of few meters represent local mean annual values, and winter-time temperatures of the ground surface. In winter, warmer, buoyant air from depth rises to the ground surface through open cracks and joints, and the temperature contrast can be detected by IRT. Our test survey was conducted in the beginning of February 2012, in order to achieve the best contrast between temperatures around open tension cracks and the adjacent ground. For temperature sensing, we used a FLIR B360 thermal camera; for airborne surveys in the ambient air, temperatures at the time of our surveys ranged from approximately −19 to −7 °C. IRT results conclusively revealed the presence of open cracks, loosened rock zones, and pseudo-karst caves over a distance sometimes greater than 1 km. The IRT approach proved useful for rapidly assessing the distribution of open cracks and tension fractures, key information required for assessing rockfall and rockslide hazard.

Cosmogenic nuclide dating of rocksildes/rock avalanches compared with other dating methods

In mountain ranges deep-seated gravitational slope deformations (DSGSDs) and extremely rapid mass wastings of rock > 105 m3 in volume (catastrophic rock-slope failures, CRF) are present, yet their mutual relation is poorly documented. Near the Brenner Pass (1370 m asl) in the eastern Alps, five catastrophic rock-slope failures of medium- to high-grade metamorphites are clustered (‘Brenner Pass Cluster’; BPC), and three of them are related to DSGSDs. The catastrophic rock-slope failures involved volumes from 12 to 110 Mm3 and show fahrboeschung angles of 10–27°. Numerical dating (14C, 234U/230Th) suggests that all catastrophic slope failures of the BPC occurred between ≤ 13.5 and 6.2 ka. Three of the CRF events may have occurred during the Younger Dryas (12.7–11.7 ka), whereas two events occurred during the Holocene. Backwater basins dammed up by the CRFs range from 2.5 km2 (Ridnaun rock avalanche) to 15.5 km2 (Stilfes rock avalanche).Three of the catastrophic rock-slope failures are associated with and developed as a partial failure of a DSGSD. This suggests that progressively slow deformation of slopes ultimately exceeded a stability threshold, resulting in catastrophic rock-slope failures. The initial kinematic mechanisms of failure vary between large-scale toppling, wedge sliding, and planar sliding and are strongly controlled by the structural setting of the slopes.A direct connection of catastrophic mass wasting with specific palaeoclimatic conditions (e.g., phases of enhanced precipitation) is not indicated; however, this does not exclude specific meteorological situations (e.g., occurrence of short-term heavy rainfall) that may have expedited slope instability and perhaps even triggered catastrophic events.Attempts to correlate catastrophic rock-slope failures with specific palaeoclimatic regimes are still encumbered by substantial methodical uncertainties and imprecisions as well as the scarcity of dated CRF events. The mapped distribution of CRFs unequivocally indicates that structural predisposition is the most significant long-term control in forming CRF clusters.

Multitemporal evolution of Deep-seated Gravitational Slope Deformations and their role in the evolution of the geomorphological landscape of the Aosta Valley

Multitemporal evolution of Deep-seated Gravitational Slope Deformations and their role in the evolution of the geomorphological landscape of the Aosta Valley

Large-scale deformational systems in the South Polar Layered Deposits (Promethei Lingula, Mars): “Soft-sediment” and Deep-Seated Gravitational Slope Deformations Mechanisms

The present study is the first attempt at a detailed structural and kinematic analysis of large-scale deformational systems observed in the South Polar Layered Deposits (SPLDs) in the Promethei Lingula (PL) margins (Mars). By systematically collecting attitude data referable to previously unknown deformational structures and defining the cross-cut relationships of the structures, we reconstructed a deformational history consisting of two superimposed, well-defined stages. The first stage is dominated by large-scale strike–slip and transtensional faults arranged into conjugate systems and delimiting shear zones that show a wide range of subsidiary structures, including normal and reverse faults, drag folds, boudins, S–C tectonites and sub-horizontal interstratal shear planes marked by sygmoidal boudins. Other typical structures referable to this event are ductile folds (locally true convolute folds) and lobes (ball-and-pillow structures) affecting certain marker beds of the succession. We suggest that the structural assemblage might be the expression of a shallow soft-sediment tectonics that possibly occurred during warm periods of the South Pole climate.The second stage seems to affect the weaker and in certain cases pre-deformed stratigraphic levels of the SPLD succession. This stage is mainly characterized by extensional deformations caused by gravity. The consequence of the deformations is the nucleation of Deep-Seated Gravitational Slope Deformations (DSGSDs) marked by typical morphostructures, such as scarps, trenches and bulging basal contractant zones. These phenomena were never observed within an ice cap. According to terrestrial modeling, these slow collapses were caused by (1) the presence of detachment levels (i.e., subhorizontal bedding planes) along which the ice-sheet margins can slide and (2) the development of listric faults within the glacial mass, which merge with sub-horizontal shear planes in the subsurface.The presence of complex deformational systems in the SPLD necessarily implies that a large-scale dynamics of the ice-sheet occurred in the past. The relatively fast internal creep and basal/internal sliding, inferable from the structure assemblage, can be due to partial melting of the ice possibly caused by climatic changes in the Promethei Lingula region. In this manner, we believe that climate heating (which, according to the literature, is likely caused by orbital variations) softened some of the SPLD layers, triggering or accelerating the ice sheet’s outward movement.The evidence of a marked disharmonic deformational style through the SPLD succession suggests the possibility of local periodic compositional variations in the sequence.

MORPHOLOGICAL FEATURES OF RODORETTO VALLEY DEEP-SEATED GRAVITATIONAL SLOPE DEFORMATIONS

A new, detailed survey of the Rodoretto Valley (Western Alps, Italy) has been conducted resulting in the production of a new morphological and quaternary geological map of the area. The authors used the innovative Solid (True) Ortho-Photo (STOP) technology integrated with navigation sensors (Global Navigation Satellite System-GNSS/Inertial Measurement Unit-IMU). This state-of-the-art procedure has demonstrated several operational advantages during both the land survey and the post-processing phases. The survey highlighted remarkable glacial evidences and landforms probably connected with Deep-Seated Gravitational Slope Deformations (DSGSDs) phenomena. The glacial forms which have been detected consist of diffuse relics of cirques, glacial slopes, small lateral and frontal moraines and some outwash incisions. The deposits associated with the relics are lodgment till, flowtill and outwash sediments, respectively. The gravitational evidences and the very fractured bedrock that has been recognized on both sides of the Rodoretto Valley, suggest the presence of two DSGSDs which are confirmed also by the occurrence of some doubled ridges in the higher elevation band of the slopes. Moreover, several minor scarps and many longitudinal and transversal trenches, of various size, occur in the intermediate band. Extended landslide bodies have been recognized in the lower altimetric band. The major new geological element detected and interpreted after the survey and the map production is represented by the identification of a well defined WNW-ESE trend of fractured rocks and gravitational landforms. The observed fractures are not limited to the Rodoretto Valley, suggesting the possible connection of the described gravitational landforms with a tectonic discontinuity with the same WNW-ESE trend. This tectonic discontinuity crosses the Cenischia-Nizza System in a zone highlighted by a portion of intensively fractured rocks.

Back analysis of a rock landslide to infer rheological parameters

On 30 January 2009, a rock slide involving approximately 0.23Mm3 of highly jointed gneiss from the local Ercinic substratum was recorded in southern Italy. The landslide occurred after exceptional autumnal rainfalls and involved a quarry whose activity has been documented over the past 10years by aerial images.An engineering-geology model of the slope involved in the landslide was developed based on the geomechanical classification of the outcropping rock masses, the ISRM (2007) indexes Ib (the block size index) and Jv (the volumetric joint count), and the observed geological setting of the slope. An equivalent continuum approach was adopted to attribute strength and stiffness parameter values to the different classes of jointed rock masses.A simplified evolutionary model of the slope was developed, starting from 300ka (i.e., from the erosional phase following the deposition of the 300-m-a.s.l. marine terrace deposits overlaying the gneiss substratum) to 30 January 2009. The model took into account the main depositional phases as indicated by the Pleistocene marine terrace deposits and the documented stages of quarry activity.Time-dependent stress–strain numerical modelling was performed by the FDM software FLAC 6.0. A visco-plastic Burger model was used to back-analyse the landslide event and to define the values of the rheological parameters for the jointed gneiss.The results, which were strongly constrained by the geomorphological evidences and by the displacement field observed before and after the landslide, demonstrated a combination of i) time-dependent gravitational slope deformation and ii) anthropogenic release due to quarry activity, which induced a progressive failure process and an increase in the jointing within the gneissic rock mass located behind the cut-wall of the quarry. Failure was ultimately triggered by intense rainfalls that occurred in the 3months before the landslide.The stress–strain numerical modelling demonstrated the reliability of visco-plastic rheology for simulating the rock mass creep in this case history: viscosity values in the range of 1019–1023Pa·s were derived.

The interaction between active normal faulting and large scale gravitational mass movements revealed by paleoseismological techniques: A case study from central Italy

Paleoseismological techniques have been applied to characterize the kinematic behaviour of large-scale gravitational phenomena located in proximity of the seismogenic fault responsible for the Mw 7.0, 1915 Avezzano earthquake and to identify evidence of a possible coseismic reactivation. The above mentioned techniques were applied to the surface expression of the main sliding planes of the Mt. Serrone gravitational deformation, located in the southeastern border of the Fucino basin (central Italy). The approach allows us to detect instantaneous events of deformation along the uphill-facing scarp. These events are testified by the presence of faulted deposits and colluvial wedges. The identified and chronologically-constrained episodes of rapid displacement can be probably correlated with seismic events determined by the activation of the Fucino seismogenic fault, affecting the toe of the gravitationally unstable rock mass. Indeed this fault can produce strong, short-term dynamic stresses able to trigger the release of local gravitational stress accumulated by Mt. Serrone's large-scale gravitational phenomena.The applied methodology could allow us to better understand the geometric and kinematic relationships between active tectonic structures and large-scale gravitational phenomena. It would be more important in seismically active regions, since deep-seated gravitational slope deformations can evolve into a catastrophic collapse and can strongly increase the level of earthquake-induced hazards.

Ruinon landslide (Valfurva, Italy) activity in relation to rainfall by means of GBInSAR monitoring

The active Ruinon rockslide is located on the left bank of the Frodolfo River valley (Valfurva, Italian Alps) and is developed on the Confinale deep-seated gravitational slope deformation. Ruinon landslide is a major hazard for valley inhabitants in that rapid movement might dam the stream and create a debris flow. The landslide is strongly controlled by preexisting structural features and is believed to have been triggered by postglacial debuttressing. Ground-based radar interferometry has been used to map surface deformation over time of the entire unstable zone of Ruinon landslide with high spatial resolution and at a very high temporal acquisition rate (about five images per hour). The activity of the landslide shows strong periodicity, with summer and autumn accelerations and winter deceleration. From a correlation between the landslide acceleration and a class of rainfall event, we deduce the specific rainfall conditions that accelerate the instability of the landslide area. The study results suggest an improved tool for early warning of events of potentially catastrophic landslide instability.

Equatorial glaciations on Mars revealed by gravitational collapse of Valles Marineris wallslopes

Martian global climate models that account for evidence of past glaciations reported in tropical to mid-latitude regions of Mars predict accumulation of water ice in Valles Marineris during past periods of high obliquity. Observational evidence for such glaciations is given here. Topographic basement ridges of tectonic origin are common in Valles Marineris, and display sackung features, an assemblage of tectonic patterns that are diagnostic of deep-seated gravitational slope deformation. This deformation is most easily explained by paraglacial ridge failure subsequent to ridge wall debuttressing and decohesion following the retreat of glaciers. This interpretation is supported by extensive bibliographic analysis of sackung triggers on Earth, by morphological evidence of subglacial erosion of the lower parts of Valles Marineris wallslopes, of periglacial erosion of their upper parts and by the presence of various types of glacial landforms on the floors of Valles Marineris troughs. The age of these equatorial glaciations is found to be older than 1.4 Gy and younger than 3.5 Gy.

Influence of structural heterogeneities and of large scale topography on imbricate gravitational rock slope failures: New insights from 3-D physical modeling and geomorphological analysis

Initial topography and inherited structural discontinuities are known to play a dominant role in rock slope stability. Previous 2-D physical modeling results demonstrated that even if few preexisting fractures are activated/propagated during gravitational failure all of those heterogeneities had a great influence on mobilized volume and its kinematics. The question we address in the present study is to determine if such a result is also observed in 3-D. As in 2-D previous models we examine geologically stable model configuration, based upon the well documented landslide at Randa, Switzerland. The 3-D models consisted of a homogeneous material in which several fracture zones were introduced in order to study simplified but realistic configurations of discontinuities (e.g. based on natural example rather than a parametric study). Results showed that the type of gravitational failure (deep-seated landslide or sequential failure) and resulting slope morphology evolution are the result of the interplay of initial topography and inherited preexisting fractures (orientation and density). The three main results are i) the initial topography exerts a strong control on gravitational slope failure. Indeed in each tested configuration (even in the isotropic one without fractures) the model is affected by a rock slide, ii) the number of simulated fracture sets greatly influences the volume mobilized and its kinematics, and iii) the failure zone involved in the 1991 event is smaller than the results produced by the analog modeling. This failure may indicate that the zone mobilized in 1991 is potentially only a part of a larger deep-seated landslide and/or wider deep seated gravitational slope deformation.

Slope instability induced by volcano-tectonics as an additional source of hazard in active volcanic areas: the case of Ischia island (Italy)

Ischia is an active volcanic island in the Gulf of Naples whose history has been dominated by a caldera-forming eruption (ca. 55 ka) and resurgence phenomena that have affected the caldera floor and generated a net uplift of about 900 m since 33 ka. The results of new geomorphological, stratigraphical and textural investigations of the products of gravitational movements triggered by volcano-tectonic events have been combined with the information arising from a reinterpretation of historical chronicles on natural phenomena such as earthquakes, ground deformation, gravitational movements and volcanic eruptions. The combined interpretation of all these data shows that gravitational movements, coeval to volcanic activity and uplift events related to the long-lasting resurgence, have affected the highly fractured marginal portions of the most uplifted Mt. Epomeo blocks. Such movements, mostly occurring since 3 ka, include debris avalanches; large debris flows (lahars); smaller mass movements (rock falls, slumps, debris and rock slides, and small debris flows); and deep-seated gravitational slope deformation. The occurrence of submarine deposits linked with subaerial deposits of the most voluminous mass movements clearly shows that the debris avalanches impacted on the sea. The obtained results corroborate the hypothesis that the behaviour of the Ischia volcano is based on an intimate interplay among magmatism, resurgence dynamics, fault generation, seismicity, slope oversteepening and instability, and eruptions. They also highlight that volcano-tectonically triggered mass movements are a potentially hazardous phenomena that have to be taken into account in any attempt to assess volcanic and related hazards at Ischia. Furthermore, the largest mass movements could also flow into the sea, generating tsunami waves that could impact on the island’s coast as well as on the neighbouring and densely inhabited coast of the Neapolitan area.