Fallout and distribution of volcanic ash over Argentina following the May 2008 explosive eruption of Chaitén, Chile

Abstract

The major explosive eruption of Chaitén volcano, Chile, in May 2008 provided a rare opportunity to track the long‐range dispersal and deposition of fine volcanic ash. The eruption followed ∼10,000 years of quiescence, was the largest explosive eruption globally since Hudson, Chile, in 1991, and was the first explosive rhyolitic eruption since Novarupta, Alaska, in 1912. Field examination of distal ashfall indicates that ∼1.6 × 1011 kg of ash (dense rock equivalent volume of ∼0.07 km3) was deposited over ∼2 × 105 km2 of Argentina during the first week of eruption. The minimum eruption magnitude, estimated from the mass of the tephra deposit, is 4.2. Several discrete ashfall units are identifiable from their distribution and grain size characteristics, with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes. Ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3–6 km. Deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption, which in this case comprised several phases over a week‐long period of intense activity.