Self‐Entrainment Motion of a Slow‐Moving Landslide Inferred From Landsat‐8 Time Series

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Quaternary volcanism in the Yura Monogenetic Field near Arequipa city, southern Peru

International audienceArequipa (Peru) is an area where volcanic activity has been persistent during the Quaternary. Studies carried out in this area have highlighted the emplacement of ignimbrite deposits, large volcanic clusters and stratovolcanoes. Monogenetic volcanism is also present, although poorly explored and studied. Due to its location over an ignimbrite plain and poor state of preservation, the only identified monogenetic cone in the Arequipa basin was the Nicholson volcano, while other monogenetic centers remained unknown. This lack of information about the recent volcanism can lead to inadequate definition of scenarios in a hazard assessment in the region. The present study has investigated monogenetic volcanism in the northwestern edge of the Arequipa basin based on geological survey, geochronology and geochemical data. Here, we report for the first time five small volcanic centers such as Yura Viejo, Ccapua, Uyupampa, El Chiral and Patacocha, which together with the Nicholson volcano form the Yura Monogenetic Field. Stratigraphic considerations and new 40Ar/39Ar ages allow us to place the eruptive activity in the Middle–Upper Pleistocene (c. 195–54 ka). Phreatomagmatic, Strombolian and effusive eruptions characterize the monogenetic activity of the field. As a result of these eruptions, small scoria cones, maars, and lava flows/coulées were generated. The eruptive products show ubiquitous olivine phenocryst-rich (<10 vol%) set in a fine pilotaxitic groundmass, suggesting rapid ascent of basaltic magmas to the surface controlled by the tectonic setting. The analyzed rocks lie in a narrow range of basaltic-andesite composition (50.9–55.6 wt% SiO2) being the most mafic Pleistocene - Recent volcanic products identified in the Arequipa basin, along with the least differentiated magmas from the nearby Chachani volcanic cluster. This work shows how monogenetic volcanism can occur contemporaneous and closely spaced to larger volcanic clusters and active stratovolcanoes. We hope the information provided here will contribute to improve the risk management by highlighting the scenario of monogenetic eruptions that should be considered in the hazard assessment. Copyrigh

Magma extrusion during the Ubinas 2013-2014 eruptive crisis based on satellite thermal imaging (MIROVA) and ground-based monitoring

International audienceAfter 3 years of mild gases emissions, the Ubinas volcano entered in a new eruptive phase on September 2nd, 2013. The MIROVA system (a space-based volcanic hot-spot detection system), allowed us to detect in near real time the thermal emissions associated with the eruption and provided early evidence of magma extrusion within the deep summit crater. By combining IR data with plume height, sulfur emissions, hot spring temperatures and seismic activity, we interpret the thermal output detected over Ubinas in terms of extrusion rates associated to the eruption. We suggest that the 2013–2014 eruptive crisis can be subdivided into three main phases: (i) shallow magma intrusion inside the edifice, (ii) extrusion and growing of a lava plug at the bottom of the summit crater coupled with increasing explosive activity and finally, (iii) disruption of the lava plug and gradual decline of the explosive activity. The occurrence of the 8.2 Mw Iquique (Chile) earthquake (365 km away from Ubinas) on April 1st, 2014, may have perturbed most of the analyzed parameters, suggesting a prompt interaction with the ongoing volcanic activity. In particular, the analysis of thermal and seismic datasets shows that the earthquake may have promoted the most intense thermal and explosive phase that culminated in a major explosion on April 19th, 2014. These results reveal the efficiency of space-based thermal observations in detecting the extrusion of hot magma within deep volcanic craters and in tracking its evolution. We emphasize that, in combination with other geophysical and geochemical datasets, MIROVA is an essential tool for monitoring remote volcanoes with rather difficult accessibility, like those of the Andes that reach remarkably high altitudes