Pablo Euillades

Morphometry and evolution of arc volcanoes

Volcanoes change shape as they grow through eruption, intrusion, erosion, and deforma- tion. To study volcano shape evolution we apply a comprehensive morphometric analysis to two contrasting arcs, Central America and the southern Central Andes. Using Shuttle Radar Topography Mission (SRTM) digital elevation models, we compute and defi ne parameters for plan (ellipticity, irregularity) and profi le (height/width, summit/basal width, slope) shape, as well as size (height, width, volume). We classify volcanoes as cones, sub-cones, and massifs, and recognize several evolutionary trends. Many cones grow to a critical height (~1200 m) and volume (~10 km 3 ), after which most widen into sub-cones or massifs, but some grow into large cones. Large cones undergo sector collapse and/or gravitational spreading, without sig- nifi cant morphometry change. Other smaller cones evolve by vent migration to elliptical sub- cones and massifs before reaching the critical height. The evolutionary trends can be related to magma fl ux, edifi ce strength, structure, and tectonics. In particular, trends may be controlled by two balancing factors: magma pressure versus lithostatic pressure, and conduit resistance versus edifi ce resistance. Morphometric analysis allows for the long-term state of individual or volcano groups to be assessed. Morphological trends can be integrated with geological, geophysical, and geochemical data to better defi ne volcano evolution models.

NETVOLC: An algorithm for automatic delimitation of volcano edifice boundaries using DEMs

Abstract Accurately delimiting boundaries is required for characterizing landforms through measurement of their geomorphometric parameters. Volcanism produces a wide range of landforms, from symmetric cones to very irregular massifs, that can gradually merge with the surroundings and contain other elements, thus complicating landform delimitation. Most morphometric studies of volcanoes delimit landforms manually, with the inconvenience of being time-consuming and subjective. Here we propose an algorithm, NETVOLC, for automatic volcano landform delimitation based on the premise that edifices are bounded by concave breaks in slope. NETVOLC applies minimum cost flow (MCF) networks for computing the best possible edifice outline using a DEM and its first- and second-order derivatives. The main cost function considers only profile convexity and aspect; three alternative functions (useful in complex cases) also consider slope, elevation and/or radial distance. NETVOLC performance is tested by processing the Mauna Kea pyroclastic cone field. Results using the main cost function compare favorably to manually delineated outlines in 2/3rds of cases, whereas for the remaining 1/3rd of cases an alternative cost function is needed, introducing some degree of subjectivity. Our algorithm provides a flexible, objective and time-saving tool for automatically delineating volcanic edifices. Furthermore, it could be used for delineating other landforms with concave breaks in slope boundaries. Finally, straightforward modifications can be implemented to extend the algorithm capabilities for delimiting landforms bounded by convex breaks in slope, such as summit craters and calderas.

Ground Deformation Between 2002 and 2013 from InSAR Observations

Ground deformation is one of the main geophysical methods for volcano monitoring. Surface deformation patterns can provide important insights into the structure, plumbing system, and state of restless volcanoes. Copahue volcano is one of the most active eruptive centers in Argentina, and a major risk factor for the nearby towns of Caviahue and Copahue. Historic eruptive activity involved low intensity phreatic and phreatomagmatic events in 1992, 1995 and 2000. A new eruptive cycle is ongoing since June 2012, with several phreatic explosions and one phreatomagmatic—magmatic eruption on December 22nd, 2012. In this work, the Small Baseline Subsets (SBAS) DInSAR-based technique is successfully applied to compute surface displacements using the ENVISAT ASAR radar imagery during quiescent and pre-eruptive periods. Our purpose is to investigate possible sources of ground deformation to better understand the system behavior. Analytical models are used to interpret geodetic data and to constrain the parameters that characterize the source responsible for the observed deformation.

The crater lake of Copahue volcano (Argentina): geochemical and thermal changes between 1995 and 2015

Abstract The crater lake and associated hydrothermal features of Copahue volcano have been studied intensively over the last 20 years (1995–2015). The geochemical and isotopic compositions of the waters provide insights into the processes occurring in the volcanic–hydrothermal system, the crater lake and the thermal springs. Variations in the temperature and chemical composition of the waters reveal fundamental changes in the system that precede and accompany the magmatic and phreatic eruptive events at Copahue. A conceptual model of the summit system was developed involving the intrusion of slivers of magma in the hot acidic hydrothermal cell, the saturation of waters with secondary minerals leading to reduced permeability, the blocking of fluid pathways by liquid sulphur during heating events and the transport of gas from the magma through the ductile–brittle transition into the hydrothermal system. Geophysical data were integrated with the chemical data to provide new insights into the behaviour of the deep magmatic system that feeds the volcano edifice. Multidisciplinary studies were used to identify precursory signals of eruptive activity to give an early warning of pending volcanic hazards. Several geochemical ratios in river water were identified as potential indicators of upcoming volcanic activity, which could be used in co-operation with the community and local authorities to deal with these volcanic hazards.

On the Generation of Late ERS Deformation Time Series Through Small Doppler and Baseline Subsets Differential SAR Interferograms

In this letter, we investigate the potential of the small baseline subset (SBAS) differential synthetic aperture radar interferometry (DInSAR) technique to produce consistent deformation time series by using data sets of SAR images with high Doppler centroid (DC) frequencies. To cope with this issue properly, we exploited an archive of SAR scenes acquired by the European Remote Sensing 2 (ERS-2) sensor after the February 2000 three-gyroscope navigation mode failure. Our approach is oriented toward the long-term investigation of large-scale displacements with low spatial resolution (about 100 × 100 m) by processing sets of SAR images without discarding scenes depending on their DC values. Our analysis involves a set of descending SAR data frames from 1992 to 2007 relevant to the Napoli (Italy) bay area. Comparison with contemporaneous Global Positioning System measurements clearly confirms the effectiveness of the proposed approach.