Explosive eruptions associated with tephra deposits that are only exposed in proximal areas are difficult to characterize. In fact, the determination of physical parameters such as column height, mass eruption rate, erupted volume, and eruption duration is mainly based on empirical models and is therefore very sensitive to the quality of the field data collected. We have applied and compared different modeling approaches for the characterization of the two main tephra deposits, the Lower Pumice(LP) and Upper Pumice (UP) of Nisyros volcano, Greece, which are exposed only within 5 km of the probable vent. Isopach and isopleth maps were compiled for two possible vent locations (on the north and on the south rim of the caldera), and different models were applied to calculate the column height, the erupted volume, and the mass eruption rate. We found a column height of about 15 km above sea level and a mass eruption rate of about 2×10^7 kg/s for both eruptions regardless of the vent location considered. In contrast, the associated wind velocity for both UP and LP varied between 0 and 20 m/s for the north and south vent, respectively. The derived erupted volume for the south vent (considered as the best vent location) ranges between 2 and 27×10^8 m3 for the LP and between 1 and 5×10^8 m3 for the UP based on the application of four different methods (integration of exponential fit based on one isopach line, integration of exponential and power-law fit based on two isopach lines, and an inversion technique combined with an advection–diffusion model). The eruption that produced the UP could be classified as subplinian. Discrepancies associated with different vent locations are smaller than the discrepancies associated with the use of different models for the determination of erupted mass, plume height, and mass eruption rate. Proximal outcrops are predominantly coarse grained with ≥90 wt% of the clasts ranging between −6phi and 0phi. Theassociated total grainsize distribution is considered to result from a combination of turbulent fallout from both the plume margins and the umbrella region, and as a result, it is fines-depleted. Given that primary deposit thickness observed on Nisyros for both LP and UP is between 1 and 8 m, if an event of similar scale were to happen again, it would have a significant impact on the entire island with major damage to infrastructure, agriculture, and tourism. Neighboring islands and the continent could also be significantly affected

The combination of structural data from the source area and descriptive data from the deposit's carapace, as well as remote sensing and statistical analysis, allows a better understanding of the collapse, fragmentation, and propagation processes of the Frank Slide rock avalanche. The in situ observed conservation of the stratigraphic sequence of the Turtle Mountain anticline's normal limb in the deposit is interpreted as the consequence of the collapse mode, involving simple shearing of the mass accompanied by a rotational movement, i.e., a "simple shear" parallel to the topography, and a breakage of the hinge, followed by overthrusting of the normal limb on the inverse limb. Coherence between the block size distributions of the source area and the deposit carapace is interpreted as a demonstration of the primary control of preexisting fracturing on the fragmentation processes. Remote-sensing indexes allow us to uncover a priori hidden morphological features preserved on the surface of the deposit, i.e., longitudinal and compressional features, as well as lobes. Their location on the carapace provides evidence of lateral heterogeneity in the propagation, highlighted by three different types of propagation behaviors. This comprehensive study not only provides elements that contribute to an understanding of the Frank Slide rock avalanche, but it also provides insight into essential parameters to take into account in further modeling of these types of phenomena.

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Rock avalanches are extremely destructive and uncontrollable events that involve a great volume of material (> 10 6 m 3 ) and several complex processes, and they are difficult to witness. For this reason the study of these phenomena using analog modeling and the accurate analysis of deposit structures and features of laboratory data and historic events become of great importance in the understanding of their behavior.The main objective of this research is to analyze rock avalanche dynamics and deformation process by means of a detailed structural analysis of the deposits coming from data of 3-D measurements of mass movements of different magnitudes, from decimeter level scale laboratory experiments to well-studied rock avalanches of several square kilometers' magnitude.Laboratory experiments were performed on a tilting plane on which a certain amount of a well-defined granular material is released, propagates and finally stops on a horizontal surface. The 3-D geometrical model of the deposit is then obtained using either a scan made with a 3-D digitizer (Konica Minolta VIVID 9i) or a photogrammetric method called structure from motion (SfM), which requires taking several pictures from different point of view of the object to be modeled.In order to emphasize and better detect the fault structures present in the deposits, we applied a median filter with different moving window sizes (from 3 × 3 to 9 × 9 nearest neighbors) to the 3-D datasets and a gradient operator along the direction of propagation.The application of these filters on the datasets results in (1) a precise mapping of the longitudinal and transversal displacement features observed at the surface of the deposits and (2) a more accurate interpretation of the relative movements along the deposit (i.e., normal, strike-slip, inverse faults) by using cross sections. Results show how the use of filtering techniques reveals disguised features in the original point cloud and that similar displacement patterns are observable both in the laboratory simulation and in the real-scale avalanche, regardless the size of the avalanche. Furthermore, we observed how different structural features, including transversal fractures and folding patterns, tend to show a constant wavelength proportional to the size of the avalanche event.Published by Copernicus Publications on behalf of the European Geosciences Union. 744 C. Longchamp et al.: 3-D models and structural analysis of rock avalanches