Multiphysical modelling for thermo-mechanical behaviour of rock masses in slope-scale gravitational dynamics

Volcanic and glacial valley systems are geological context where Deep Seated Gravitational Slope Deformations (DSGSDs) frequently evolve. These areas experienced in their geological history significant variation in stress field due to the rapid growth of volcano flanks or glacial debuttressing rebound, respectively. In addition to these effects, a less importance have been given to multi-physical interactions between the slopes and the natural systems in which the DSGSD can evolved. In order to evaluate the role of physical or multi-physical interaction in dictating time-dependant slope-scale gravitational deformation processes, a numerical analysis has been approached reproducing by stress-strain and thermo-hydrodynamical modelling, the mutual interaction between thermal and mechanical processes in slope stability. With the purpose to evaluate and constrain the inner forcings related to deep systems which can influence the gravitational process acting in the slopes, the combination of models at different geometric-scales have been experimented. Basing on two selected case study, representative of two thermal end-member (i.e. warm and cold systems) the influence of thermo-mechanical processes in gravity-induced deformations was evaluated by adopting different solving schemes as function of the stationarity or transiency of the systems within an observation time-window. Coupled or Uncoupled solution between two or more physics were experimented reproducing sequential evolution of slope system with the support of FDM and FEM numerical codes. A process of validation of the Thermal and the Mechanical models defined for both deep- and slope-scales were achieved by means of sensitivity and parametric analysis. The validated models were then used for the formulation of physically-based scenarios, defined to evaluate the role of multiple factors in the onset or time-evolution of slope deformation. The adopted approach represented an useful tool to evaluate the proneness of DSGSDS to paroxysmal tertiary failure and in the definition multi-hazard scenarios related to slope instabilities

Geological constraints for a conceptual evolutionary model of the slope deformations affecting Mt. Nuovo at Ischia (Italy)

ischia island was the scenario of several Holocene slope in- stability events occurred at different scales, from shallow mass movements, triggered by meteo-climatic forcing, up to massive rock slope failures such as large debris avalanches these last ones related to the volcano-tectonic dynamics of a resurgent caldera. the present study focuses on the gravitational deformation that in- volves Mt. nuovo, located in the western portion of Mt. epomeo resurgent block. a high-resolution engineering-geological model was reconstructed according to a multi-modelling approach sup- ported by field geo-structural evidences and constrained by pas- sive seismic investigations. it revealed a complex morpho-struc- tural setting and led to the identification of a multiple compound mechanism, involving a rock mass volume of about 190 million of cubic meters. the obtained geological model shows a partial structural control of the pre-existing tectonic pattern on slope deformation mechanisms, highlighting geometric and volumetric similarities between the Mt. nuovo ongoing deformation and an already oc- curred rock avalanche. the defined conceptual evolutionary mod- el allows to hypothesize the role of inner pressures constraining the shear zone initiation and propagation and making reliable a future scenario of generalized collapse. Starting from these new field and laboratory data, numerical models will be reconstructed in order to depict the evolution of the gravitational slope deformation, evaluate its sensitivity and constrain future evolutionary instability scenarios

Experimental evidences of thermo-mechanical induced effects on jointed rock masses through infrared thermography and stress-strain monitoring

The Mediterranean area is subjected to considerable daily and seasonal thermal variations due to intense solar radiation. This effect influences the long-term behaviour of jointed rock masses, operating as thermal fatigue process and acting as a preparatory factor for rock failures. In order to quantify intensity and influence of thermo-mechanical effects on rock slope stability, a multi-parametric monitoring is operative in an abandoned limestone quarry at Acuto (central Italy) by remote (i.e. IR Thermography) and direct (i.e. thermocouple and strain sensors) sensing techniques. The monitoring system has been focused on an intensely jointed rock block. Several joints bound a prismatic-shaped volume, isolate it from the rock wall behind and cause its protrusion respect to the quarry wall so increasing proneness to fall and toppling. Preliminary data analyses highlight the cyclical deformative response of block to thermal forcing, revealing the effect of sun radiation and exposure because of the heating of the rock surface

Multi-modelling for a slope-scale deformation evolving from mass rock creep to rock avalanche

The here presented study analyses the combined role of geological and morphological features on the evolution of an ongoing gravitational slope deformation, located in the western portion of the Mt. Genzana Ridge (central Italy). The latter partly evolved in a huge rock-avalanche responsible for damming the Tasso River valley and originating the Scanno Lake. A morpho-structural multi-stage model of the Quaternary evolution of the slope was reconstructed through geomorphological analyses and a time-dependent morphometric approach. Based on the morpho-evolutionary model we performed a stress-strain numerical modeling to back-analyze the processes that led to the onset of the rockslope deformation. The numerical analysis took into account: i) age constraints derived from morpho-evolutionary model; ii) engineering-geological model based on equivalent continuum approach and a statistical distribution of geomechanical parameter together with targeted laboratory tests; iii) regional stress-field regime variation connected with tectonic activity; iiii) viscous time-dependent behavior. In this paper the results of the multi-modeling approach are presented presents and discussed

Morpho-structural evolution of the valley-slope systems and related implications on slope-scale gravitational processes. New results from the Mt. Genzana case history (Central Apennines, Italy)

This work is aimed at constraining a slope-scale, deep-seated gravitational slope deformation (DSGSD) and an associated rockslide-avalanche in the frame of the Quaternary morpho-structural evolution of Central Apennines (Italy). The study area is the western slope of the Mt. Genzana calcareous ridge, for which a conceptual slope evolutionary model had been already proposed. The existing model has highlighted the role of inherited geological-structural setting combined with Quaternary morpho-evolution in the onset of rock-slope deformational processes until paroxysmal phases (i.e. occurrence of massive rock slope failures). In this work, the previous conceptual evolutionary model was strengthened and detailed by means of a mid-term landscape evolution model, based on the study of geomorphic markers hanging at different elevations above the present valley floor. The Quaternary landscape evolution was also constrained by means of time-dependent landscape metrics. Consequently, it was possible to back-analyse the observed DSGSD process from its onset up to the occurrence of localized massive rock slope failures, through a time-dependent stress–strain numerical modeling. The results of such a multi-modeling approach: i) highlighted the importance of rock mass creep during some stages of the morpho-evolution; ii) pointed out the relevant role of the inherited structural pattern in identifying the preferential strain concentration zones and failure surfaces; and iii) confirmed the hypothesis that the Scanno rockslide-avalanche scar is the result of two separate failure events, as an initial landslide involving the lower part of the slope that favoured a subsequent failure in the upper part of the slop

High-resolution geological model of the gravitational deformation affecting the western slope of Mt. Epomeo (Ischia)

The recent geological history of Ischia Island is characterized by slope-scale gravitational deformations closely related to volcano-tectonic dynamics of the Mt. Epomeo resurgent caldera. This study focuses on the gravitational deformation that involves alkali-trachytic lava and trachytic ignimbrite flow-units of Mt. Nuovo, located in the western portion of Mt. Epomeo. A preliminary, high-resolution engineering-geological model was obtained through geological, geomorphological and geophysical surveys and reveals a complex morpho-structure with geomorphological evidence of gravitational instability. The complexity of the ongoing slope deformations is confirmed by field geo-structural evidences that led to the identification of a multiple compound mechanism with a main rupture surface which is about 200 m deep. This geometry was better constrained by passive seismic investigations consisting in noise measurements, focused on resonance frequencies of the soil (i.e. based on H/V Nakamura approach). In addition, a close relationship between the outcrop of Mt. Epomeo Green Tuff breccia layers and the distribution of hydrothermal emissions and gas vent can be inferred, as it is related to the higher permeability of the breccia layers with respect to the main Mt. Epomeo Green Tuff flow unit, where the ascent path of deep hydrothermal fluids developed along faults and fracture networks

1D Numerical modelling of crustal heat transfer in the Antarctic glaciers of Northern Victoria Land

The Antarctic glacial system is both highly sensitive to, and driver of global climate changes being as well sensitive to other external events, such as endogenous factors, that may affect glaciers energy balance. In this framework, thermal regime and heat flow evolution within the continental crust below the ice sheet must be considered. The present work focused on preliminary result of 1D numerical modelling of pure conductive heat transfer model pointing out the role of several factor in crustal heat transfer and its effects of thermal regime of east Antarctic glacial system. Here we present a case study on northern Victoria Land (Antarctica) glacial system ,a key site for investigating the amplitude of past ice volume variations in the East Antarctic Ice Sheet (EIAS, Baroni et al.[1]), comprising a relevant sector of the Transantarctic Mountains and the Mt. Melbourne Volcanic Province (MVP). With the support of thermo-barometric data obtained by the study of spinel-peridotites xenoliths, Armienti and Perinelli [2] inferred a change of mantle’s geothermal gradients from 0.5 °C/km to 3 °C/km, as response to lithospheric thinning caused by Ross Sea Rifting. On the basis of such petrologic and geo-thermometric data, combined, in a first analysis, with bibliographic thermal properties of rock materials, a simulation of the heat flow propagation from the upper mantle across the continental crust has been performed. These data provided the input for a multi-parametric analysis that has assumed a stationary and conductive heat flow and was performed through a sensitivity approach by varying thermal parameters and stratigraphic profiles, i.e. considering different thickness for the different proportions of the continental crust. A local heat source in the upper crust has been also considered and no surficial thermal perturbation due to volcanic systems were modelled. The numerical model so defined, took into account a crustal heat flux of 120 mW/m2 (Della Vedova et al. [3]), typical value of Victoria Land Basin, and temperature values at Moho ranging between 750 and 1450 °C. In addition we considered a sensitivity analysis to the ice thickness of the glacial system up to 800 m, according to Pleistocene EAIS variations and ice fluctuations amplitudes reconstructed in NVL (Strasky et al.[4]). At lateral boundary of 1D model a thermal isolation has been also assumed. The 1D thermal model, has been validated matching experimental data obtained from a nearby deep borehole (Morin et al. [5]), assumed as reference point, representative of the geodynamic and volcanic conditions of the study area, in which a temperature of about 75 °C at depth of 1000 m b.s.l. has been reached. The modelling provides encouraging results, highlighting a main contribution of regional heat source and ice sheet thickness on the thermal regime of the upper crust respect to geometrical and thermal parameters. Our results lead to a deep origin in thermal perturbations of glacial system, which seems to be less sensitive to thermal anomalies in the upper crust. Notably, the high pressure accumulation (i.e. upper mantle/lower crust) of hot parental magmas in the Ross Island and MVP, that has been proposed on the basis of experimental (Iacovino et al. [6]) and cumulate rocks (Perinelli and Gaeta [7]) studies, proves the regional, deep thermal perturbations beneath the studied area. The 1D thermal model represent the basis for further analysis focused on the evaluation of thermo-mechanical interactions between bedrock and ice masses with particular interest on stress-strain effects on the kinematic of the glaciers. References: [1] Baroni et al. (2005)Bulletin of the Geological Society of America 117: 212-228 [2] Armienti and Perinelli C. (2010)Tectonophysics 486: 28–35. [3] Della Vedova et al. (1992) In: Proceedings of the 6th ISAES: Saitama, Japan, 627–637. [4] Strasky et al. (2009) Antarctic Science21: 59–69. [5] Morin et al. (2010) Geosphere 6: 370–378. [6] Iacovino et al. (2016) Journal of Petrology doi: 10.1093/petrology/egv083. [7] Perinelli and Gaeta (submitted) Periodico di Mineralogi