Tephra stratigraphy and eruptive volume of the May, 2008, Chaitén eruption, Chile

Abstract

On May 1st 2008 Mount Chaitén (southern Chile) interrupted a long period of quiescence, generating a sequence of explosive eruptions and causing the evacuation of Chaitén town located a few kilometers south of the volcano. The activity was characterized by several explosive events each associated with plumes which reached up to about 19 km above sea level. The products were dispersed across a wide area, with the finest ash reaching the Atlantic coast of Argentina. Our field observations in the proximal-medial area (3–25 km from the vent) indicate that the May 2008 tephra deposit consists of numerous layers, most of which can be correlated with individual eruptive events. These layers vary from extremely finegrained ash to layers of lapilli and blocks, composed of both juvenile and lithic material. Here we describe the stratigraphy and physical characteristics of the May 2008 deposits, and propose a reconstruction of the timing of the May 2008 events. The deposits are mainly associated with the three main explosive phases which occurred on 1st–2nd May, 3rd–5th May and 6th May, with an estimated bulk tephra volume of 0.5–1.0 km3 (integration of both exponential and power-law fitting). For the 6th May event, represented by a layer composed mainly of lithic lapilli and blocks (>2 mm), an isopleth map was compiled from which a 19 km plume height was determined, which is in good agreement with satellite observations

Acute sedimentation response to rainfall following the explosive phase of the 2008–2009 eruption of Chaitén volcano, Chile

“…Intermittent large explosions from May 2-8 generated many-kilometers-high eruption columns, with the plume from the climactic explosion on May 6 rising to 20+ km (Carn et al 2009;Durant et al 2012). Tephra fall initially blanketed the region ESE of the volcano from May 3-5 (Alfano et al 2011;Osores et al 2013). A large eruption column drifting NE on May 6 produced the thickest and coarsest tephra layer, one rich in lithic rhyolite particles (β-layer of Alfano et al 2011Alfano et al , 2012.…”

“…Tephra fall initially blanketed the region ESE of the volcano from May 3-5 (Alfano et al 2011;Osores et al 2013). A large eruption column drifting NE on May 6 produced the thickest and coarsest tephra layer, one rich in lithic rhyolite particles (β-layer of Alfano et al 2011Alfano et al , 2012. Another substantial explosion occurred on May 8 (Lara 2009;Durant et al 2012).…”

“…Tephra from that explosion drifted mainly to the east, although close to the volcano it may also have drifted NE to SE (e.g., Osores et al 2013). Explosive activity waned after May 8, and effusive activity began about May 12 (Carn et al 2009;Pallister et al 2013a), but minor quantities of fine ash continued to accumulate in the basin through early 2009 (Alfano et al 2011). Escalating explosive activity prompted a full evacuation of the town of Chaitén (population ∼4,600) by May 6.…”

“…1 Locations of Chaitén lava dome (red triangle); Chaitén caldera (black outlined polygon around red triangle in lower map); Chaitén town (red dot on lower map), 10 km SW of the volcano at the mouth of Chaitén River; the informally named Chaitén River tributaries, Caldera Creek, and East Fork; and regional rain gauges (yellow dots on upper map). Tephra isopachs (in red) across Chaitén River drainage basin (outlined in black) are for minimum total tephra accumulation from the 2008-2009 eruption and are based on a total-thickness isopach map of Alfano et al (2011), supplemented with unpublished field measurements within the basin. Mapped tephra thicknesses are minimum values owing to considerable surface erosion that occurred prior to field measurements.…”

“…The early explosive phase of the 2008-2009 eruption produced a widespread fall of pumiceous tephra (particles to at least 10 cm diameter), but the upper layers of the tephra blanket were dominated by fine to extremely fine ash (0.250 to <0.063 mm) (White and Houghton 2006;Alfano et al 2011;J. Castro, Johannes Gutenberg Universität Mainz, 2012, written communication).…”