The role of dyking and fault control in the rapid onset of eruption at Chaitén volcano, Chile

Abstract

Rhyolite is the most viscous of liquid magmas, so it was surprising that on 2 May 2008 at Chaitén Volcano, located in Chile's southern Andean volcanic zone, rhyolitic magma migrated from more than 5 km depth in less than 4 hours (ref. 1) and erupted explosively with only two days of detected precursory seismic activity. The last major rhyolite eruption before that at Chaitén was the largest volcanic eruption in the twentieth century, at Novarupta volcano, Alaska, in 1912. Because of the historically rare and explosive nature of rhyolite eruptions and because of the surprisingly short warning before the eruption of the Chaitén volcano, any information about the workings of the magmatic system at Chaitén, and rhyolitic systems in general, is important from both the scientific and hazard perspectives. Here we present surface deformation data related to the Chaitén eruption based on radar interferometry observations from the Japan Aerospace Exploration Agency (JAXA) DAICHI (ALOS) satellite. The data on this explosive rhyolite eruption indicate that the rapid ascent of rhyolite occurred through dyking and that melt segregation and magma storage were controlled by existing faults.

Overview of Chaitén Volcano, Chile, and its 2008-2009 eruption

“…Rapid ascent of the rhyolite magma from storage along the sill resulted from vertical propagation of the dike beneath the volcano. The net decrease in volume of these three source bodies was about 10-30% of the estimated volume of erupted material (see below), which Wicks et al (2011) concludes was an expected consequence of magma compressibility.…”

“…It is located approximately in the middle of, but inland from, the zone ruptured during the M w 9.5 great Chilean earthquake of 1960 (Wang et al, 2007). Deformation modeling by Wicks et al (2011) suggests that the 2008-2009 eruption of Chaitén was fueled by magma that resides along an east-northeast dipping reverse fault related to the LOFZ (also see Piña-Gauthier et al, 2013, this volume).…”

“…1; Wang et al, 2007;Wicks et al, 2011). It is located approximately in the middle of, but inland from, the zone ruptured during the M w 9.5 great Chilean earthquake of 1960 (Wang et al, 2007).…”

“…Residents of the town of Chaitén felt earthquakes only 24 hours before the eruption produced ashfall, and petrological evidence suggests that the rhyolite magma that fueled the eruption ascended rapidly from depths of 5-9 km in as little as 4 hours (Castro and Dingwell, 2009). Analysis of Interferometric Synthetic Aperture Radar (InSAR) images suggests this rapid ascent of magma occurred through dike propagation from an inclined sill that originates beneath Michinmahuida Volcano (Wicks et al, 2011).…”

“…Lowenstern et al (2012) show that degassing of Cl and other magmatic elements was caused by near-surface crystallization of the magma. From analyses of two pairs of InSAR images of Chaitén, Wicks et al (2011) determined that three separately deforming bodies were involved in the eruption of Chaitén. They show that the ultimate source of magma at Chaitén comes from an inclined sill (the reservoir) that feeds magma diagonally upward from a source at 20 km depth beneath Michinmahuida Volcano.…”