Sedimentation of long-lasting wind-affected volcanic plumes: the example of the 2011 rhyolitic Cordón Caulle eruption, Chile

Abstract

Sedimentation processes and fragmentation mechanisms during explosive volcanic eruptions can be constrained based on detailed analysis of grain-size variations of tephra deposits with distance from vent and total grain-size distribution (TGSD). Grain-size studies strongly rely on deposit exposure and, in case of long-lasting eruptions, can be complicated by the intricate interplay between eruptive style, atmospheric conditions, particle accumulation, and deposit erosion. The 2011 Cordón Caulle eruption, Chile, represents an ideals laboratory for the study of long-lasting eruptions thanks to the good deposit accessibility in medial to distal area. All layers analyzed are mostly characterized by bimodal grain-size distributions, with both the modes and the fraction of the coarse subpopulation decreasing rapidly with distance from vent and those of the fine subpopulation being mostly stable. Due to gradually changing wind direction, the two subpopulations characterizing the deposit of the first 2 days of the eruption are asymmetrically distributed with respect to the dispersal axis. The TGSD of the climactic phase is also bimodal, with the coarse subpopulation representing 90 wt% of the whole distribution. Polymodality of individual samples is related to size-selective sedimentation processes, while polymodality of the TGSD is mostly related to the complex internal texture (e.g., size and shape of vesicles) of the most abundant juvenile clasts. The most representative TGSD could be derived based on a combination of the Voronoi tessellation with a detailed analysis of the thinning trend of individual size categories. Finally, preferential breakage of coarse pumices on ground impact was inferred from the study of particle terminal velocity

Chronology and impact of the 2011 Cordón Caulle eruption, Chile

“…Beginning of impact shows the starting date, and the duration of impact indicates the approximate number of days, weeks and months as reported in the media. Deposit thickness is observed from Pistolesi et al (2015); mean grain size is from Bonadonna et al (2015b). Towns/areas are indicated in Figs Besides the thickness, grain-size is also a very important factor affecting the type of impact.…”

“…In Ingeniero Jacobacci, the PM 10 concentrations were more than the double than in Villa La Angostura. This could be related to both the significantly finer grain size characteristic of Ingeniero Jacobacci (Bonadonna et al, 2015b), higher wind and lower rain fall (Fig. 7e, f).…”

“…2) (Bran et al, 2000(Bran et al, , 2002.The southern Andes present an average elevation at c. 2000 m, with the highest peak at Lanín volcano (3776 m above sea level; a.s.l.). The landscape is characterized by glacially sculpted steep slopes, glacial and tectonic lakes and flat valley floors of fluvial and glacio-fluvial outwash.…”

MMASTER: Improved ASTER DEMs for Elevation Change Monitoring

“…The eruption resulted in a number of substantial topographic changes: (1) the effusion of a massive, 30-45 m-thick rhyolite lava flow that emanated from an effusive vent on the NNW flank of the volcano [27], (2) the shallow emplacement of a laccolithic intrusion that triggered a >200-m bulge of the Earth's surface and (3) the thick deposition of explosive material as a result of pyroclastic flows. In addition, the eastward transport of the eruptive column led to thick ash and tephra deposits [28], which considerably affected the ecosystems of the regions east of the volcano [29], including killing the vegetation due to the toxic ash concentration. The Puyehue-Cordón Caulle volcanic complex is thus an ideal case study for assessing the relevance of our method to quantify topography changes resulting from volcanic activity.…”

Simulating a multi-phase tephra fall event: inversion modelling for the 1707 Hoei eruption of Mount Fuji, Japan

“…Inversion of analytical models is one method for the determination of physical parameters (e.g. Connor and Connor 2006;Bonasia et al 2010;Mannen 2014;Volentik et al 2010;Bonadonna et al 2015a, c) but has not been tested on a long-lasting, multi-phase volcanic eruption. Here, we present a detailed investigation of the use of analytical inversions based on application to a well-known and well-studied multi-phase eruption that occurred over a Editorial responsibility: S. A. Fagents and J. Fierstein…”