International audienceThe last three eruptions at the Cordón Caulle volcanic complex, Chile, have been strikingly similar in that they have started with relatively short pre-eruptive warning and produced chemically homogeneous rhyolite to rhyodacite magma with glassy to aphyric texture. These characteristics collectively call for an understanding of the storage conditions leading to the rise and extraction of crystal-poor silicic magma from volcanoes. We have analyzed and experimentally reproduced the mineral assemblage and glass chemistry in rhyolite magma produced in the most recent eruption of Cordón Caulle, and we use these to infer magma storage and ascent conditions. Fe-Ti oxide mineral geothermometry suggests that the rhyolite was stored at ∼870-920 °C. At these temperatures, the phenocryst assemblage (plag∼An37 > cpx + opx > mag + ilm) can be reproduced under H2O-saturated conditions of between 100 and 50 MPa, corresponding to crustal depths between about 2.5 and 5.0 km. The shallow and relatively hot magma storage conditions have implications for the rapid onset, degassing efficiency, and progression from explosive to mixed pyroclastic-effusive eruption style at Cordón Caulle
Soon after the onset of an eruption, model forecasts of ash dispersal are used to mitigate the hazards to aircraft, infrastructure, and communities downwind. However, it is a significant challenge to constrain the model inputs during an evolving eruption. Here we demonstrate that volcanic lightning may be used in tandem with satellite detection to recognize and quantify changes in eruption style and intensity. Using the eruption of Calbuco volcano in southern Chile on 22 and 23 April 2015, we investigate rates of umbrella cloud expansion from satellite observations, occurrence of lightning, and mapped characteristics of the fall deposits. Our remote sensing analysis gives a total erupted volume that is within uncertainty of the mapped volume (0.56 ± 0.28 km3 bulk). Observations and volcanic plume modeling further suggest that electrical activity was enhanced both by ice formation in the ash clouds >10 km above sea level and development of a low‐level charge layer from ground‐hugging currents.
The 10-day explosive phase at the start of the 2008-2009 eruption of Chaitén volcano in southern Chile (42.83°S, 72.65°W) blanketed the steep, rain-forestcloaked, 77-km 2 Chaitén River drainage basin with 3 to >100 cm of tephra; predominantly fine to extremely fine rhyolitic ash fell during the latter half of the explosive phase. Rain falling on this ash blanket within days of cessation of major explosive activity generated a hyperconcentratedflow lahar, followed closely by a complex, multi-day, muddy flood (streamflow bordering on dilute hyperconcentrated flow). Sediment mobilized in this lahar-flood event filled the Chaitén River channel with up to 7 m of sediment, buried the town of Chaitén (10 km downstream of the volcano) in up to 3 m of sediment, and caused the lower 3 km of the channel to avulse through the town. Although neither the nature nor rate of the sedimentation response is unprecedented, they are unusual in several ways: (1) (3) The volume of sediment eroded from hillslopes and delivered to the Chaitén River channel was at least 3-8×10 6 m 3 -roughly 15-40 % of the minimum tephra volume that mantled the Chaitén River drainage basin. (4) The acute sedimentation response to rainfall appears to have been due to the thickness and fineness of the ash blanket (inhibiting infiltration of rain) and the steepness of the basin's hillslopes. Other possible factors such as the prior formation of an ash crust, development of a hydrophobic surface layer, or large-scale destruction of rain-intercepting vegetation did not play a role.
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