Holocene tephrochronology of the Hualaihue region (Andean southern volcanic zone, ~42° S), southern Chile

Watt, S.F.L., Pyle, D.M., Naranjo, J.A., Rosqvist, G., Mella, M., Mather, T.A. and Moreno, H. (2011) Holocene tephrochronology of the Hualaihue region (Andean southern volcanic zone, ~42° S), southern Chile. Quaternary International, 246 (1-2), 324-343. (doi:10.1016/j.quaint.2011.05.029).

Abstract

Late Glacial and Holocene soils and sediments in southern Chile contain an important record of explosive volcanic activity since the end of the last glaciation, and have considerable potential for the development of a regional tephrostratigraphical framework. This paper reports the discovery of several new tephra deposits from the Hualaihue region (?42° S) of southern Chile. Eruption sizes, constrained from field observations, and ages, constrained by 25 new radiocarbon dates, show that the volcanoes of the Hualaihue peninsula have had relatively few explosive, tephra-generating eruptions during the Holocene. An eruption of Apagado deposited ?1 km3 of bedded basaltic scoria at ?2.6 calibrated (cal) ka BP, and Hornopirén produced a similar, but volumetrically-smaller unit at ?5.7 cal ka BP. Activity at Yate over the same time period has been predominantly characterised by lava production, although small explosive eruptions, the products of which span a range of compositions, have also occurred, including one at ?0.9 cal ka BP. The northern part of the regional tephra sequence is dominated by andesitic pumice fall deposits derived from Calbuco volcano. These include deposits from several eruptions during a 3500-year-long period at the start of the Holocene, as well as two large explosive eruptions in the past 2000 years. A distinctive rhyolitic tephra layer that is interbedded with the locally derived tephra sequence is the Cha1 unit, from Chaitén volcano, 108 km south of Hornopirén. This rhyolitic pumice deposit, dated at ?9.75 cal ka BP, is the largest volumetrically of those described here, with a volume of 3.5 km3. This new tephrostratigraphy covers a region whose volcanic history was previously very little known, and contributes to a regional record of large explosive eruptions that now spans a 500 km-long segment of the southern Andean arc, between Calbuco and Hudson volcanoes.

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