Uncertainties in lava flow hazard maps derived from numerical simulations: the case study of Mount Etna

The procedure for the derivation of a hazard map for lava flows at Mount Etna through lava flow simulations is critically reviewed. The DOWNFLOW code is then used to explore the sensitivity of the hazard map with respect to input settings. Three parameters are varied within ranges close to values recently applied to derive similar hazard maps: (i) the spacing between computational vents; (ii) the spatial probability density function (PDF) for future vent opening; and (iii) the expected length of future lava flows. The effect of increasing the spacing between computational vents tends to be compensated at the lower elevations, and a vent spacing smaller than about 500 m warrants an overall difference with respect to a reference map which is smaller than 6–8%. A random subsampling of the elements used to obtain the input vent opening PDF (−20%, −40% and −60%) originates significant but drastically smaller differences in the obtained map with respect to the reference one (~10%, ~12.5% and ~17% respectively, on average). In contrast, our results show that changes in the expected flow length originate, by far, the highest changes in the obtained hazard map, with overall differences ranging between ~20% and ~65%, and between ~30% and ~95% if computed only over inhabited areas. The simulations collected are further processed to derive maps of the confluence/diffluence index,which quantifies the error introduced, locally, when the position of the vent is misplaced by a given distance

A Microscopic Information System (MIS) for petrographic analysis

The database and visualization facilities of Geographic Information System (GIS) software are employed to support the analysis of rock texture from thin section by image processing. A Microscopic Information System (MIS) is hence obtained. The method is applied to transmitted light images of 137 samples obtained from 8 granitoid rocks. A slide scanner and a mount for crossed polarization are used to acquire the input images. For each thin section 5 collimated RGB images are scanned: 4 under different directions of crossed polarization and 1 without polarization. A grain segmentation procedure, based on two region growing functions is applied. The output is converted to vector format and refined using editing tools in the MIS environment, which enables a straightforward match between the input imagery and the final vectorized texture. GIS software provides optimal management of the MIS database, allowing the cumulative measurement of more than 87 000 grains

Capturing full resolution perspective and stereo views of large DEMs

A custom software to capture still views of images draped on digital surfaces is presented. It is called ViCam (for virtual camera). Unlike off the shelf software packages, our system is completely controlled by the user, allowing the visualization of a scene from an arbitrary viewpoint with an arbitrary (virtual) optic geometry (i.e. field of view angle). This software can work in loop over very large tiled datasets handled by a Geographic Information System (GIS) package, providing in output global views of the entire input area as single and seamless image layers at any desired resolution. Output image layers can be derived also in stereo anaglyph mode, allowing a thorough 3-dimensional perception of the landscape morphology as derived by the input elevation dataset. This method is here applied to two test cases showing the performances of the procedure. A website is also addressed where seamless perspective and stereo views of the landscape of the Italian territory preserving the input 10 m or 5 m resolution can be examined

Reply to the Comment on “Lost tsunami by M.T.Pareschi et al.”, by Luigi Vigliotti

No abstrac

A website to explore the TINITALY/01 DEM

In 2007, a new digital elevation model (DEM) of the whole Italian territory, named TINITALY/01, was presented by Tarquini et al. [2007]. This DEM was the final result of the DIGITALIA project supported by the Italian Ministero dell’Ambiente e della Tutela del Territorio in the framework of a general agreement involving the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The whole database of this DEM, in the form of a 10 m cell size grid, is available to the INGV research community at the web portal Kharita (http://kharita.rm.ingv.it/dmap/). Tarquini et al. [2007] mentioned in short a dedicated website (http://webgis.pi.ingv.it/), where authorized users were allowed to explore full resolution nadiral or perspective shaded relief images (in stereo or conventional format) obtained from the TINITALY/01 DEM. The navigation of this website is now opened to the public. The present technical report illustrates this website, describing its content and unfolding related technological aspects

Best-fit results from application of a thermo-rheological model for channelized lava flow to high spatial resolution morphological data

The FLOWGO thermo-rheological model links heat loss, core cooling, crystallization, rheology and flow dynamics for lava flowing in a channel. We fit this model to laser altimeter (LIDAR) derived channel width data, as well as effusion rate and flow velocity measurements, to produce a best-fit prediction of thermal and rheological conditions for lava flowing in a ~1.6 km long channel active on Mt. Etna (Italy) on 16th September 2004. Using, as a starting condition for the model, the mean channel width over the first 100 m (6 m) and a depth of 1 m we obtain an initial velocity and instantaneous effusion rate of 0.3–0.6 m/s and ~3 m3/s, respectively. This compares with field- and LIDAR-derived values of 0.4 m/s and 1–4 m3/s. The best fit between model-output and LIDAR-measured channel widths comes from a hybrid run in which the proximal section of the channel is characterised by poorly insulated flow and the medial-distal section by well-insulated flow. This best-fit model implies that flow conditions evolve down-channel, where hot crusts on a free flowing channel maximise heat losses across the proximal section, whereas thick, stable, mature crusts of ′a′a clinker reduce heat losses across the medial-distal section. This results in core cooling per unit distance that decreases from ~0.02–0.015°C m−1 across the proximal section, to ~0.005°C m−1 across the medial-distal section. This produces an increase in core viscosity from ~3800 Pa s at the vent to ~8000 Pa s across the distal section

Topographic control on lava flow paths at Mt. Etna (Italy): implications for hazard assesment

Assessment of the hazard from lava flow inundation at the active volcano of Mt. Etna (Italy) was performed by calculating the probability of lava flow inundation at each position on the volcano. A probability distribution for the formation of new vents was calculated using geological and volcanological data from past eruptions. The simulated lava flows from these vents were emplaced using a maximum expected flow length derived from geological data on previous lava flows. Simulations were run using DOWNFLOW, a DEM-based model designed to predict lava flow paths. Different eruptive scenarios were simulated by varying the elevation and probability distribution of eruptive points. Inundation maps show that the city of Catania and the coastal zone may only be impacted by flows erupted from low-altitude vents (< 1500 m elevation), and that flank eruptions at elevations > 2000 m preferentially inundate the northeast and southern sectors of the volcano as well as the Valle del Bove. Eruptions occurring in the summit area (> 3000 m elevation) pose no threat to the local population. Discrepancies between the results of simple, hydrological models and those of the DOWNFLOW model show that hydrological approaches are inappropriate when dealing with Etnean lava flows. Because hydrological approaches are not designed to reproduce the full complexity of lava flow spreading, they underestimate the catchment basins when the fluid has a complex rheology

Multiview 3D reconstruction in geosciences

Multiview three-dimensional (3D) reconstruction is a technology that allows the creation of 3D models of a given scenario from a series of overlapping pictures taken using consumer-grade digital cameras. This type of 3D reconstruction is facilitated by freely available software, which does not require expert-level skills. This technology provides a 3D working environment, which integrates sample/field data visualization and measurement tools. In this study, we test the potential of this method for 3D reconstruction of decimeter-scale objects of geological interest. We generated 3D models of three different outcrops exposed in a marble quarry and two solids: a volcanic bomb and a stalagmite. Comparison of the models obtained in this study using the presented method with those obtained using a precise laser scanner shows that multiview 3D reconstruction yields models that present a root mean square error/average linear dimensions between 0.11 and 0.68%. Thus this technology turns out to be an extremely promising tool, which can be fruitfully applied in geosciences