Explosive volcanism (VEI 6) without caldera formation: insight from Huaynaputina volcano, southern Peru

Abstract

Through examination of the vent region of Volcán Huaynaputina, Peru, we address why some major explosive eruptions do not produce an equivalent caldera at the eruption site. Here, in 1600, more than 11 km 3 DRE (VEI 6) were erupted in three stages without developing a volumetrically equivalent caldera. Fieldwork and analysis of aerial photographs reveal evidence for cryptic collapse in the form of two small subsidence structures. The first is a small non-coherent collapse that is superimposed on a cored-out vent. This structure is delimited by a partial ring of steep faults estimated at 0.85 by 0.95 km. Collapse was non-coherent with an inwardly tilted terrace in the north and a southern sector broken up along a pre-existing local fault. Displacement was variable along this fault, but subsidence of approximately 70 m was found and caused the formation of restricted extensional gashes in the periphery. The second subsidence structure developed at the margin of a dome; the structure has a diameter of 0.56 km and crosscuts the non-coherent collapse structure. Subsidence of the dome occurred along a series of up to Editorial responsibility: J. Stix seven concentric listric faults that together accommodate approximately 14 m of subsidence. Both subsidence structures total 0.043 km 3 in volume, and are much smaller than the 11 km 3 of erupted magma. Crosscutting relationships show that subsidence occurred during stages II and III when ∼2 km 3 was erupted and not during the main plinian eruption of stage I (8.8 km 3 ).The mismatch in erupted volume vs. subsidence volume is the result of a complex plumbing system. The stage I magma that constitutes the bulk of the erupted volume is thought to originate from a ∼20-km-deep regional reservoir based on petrological constraints supported by seismic data. The underpressure resulting from the extraction of a relatively small fraction of magma from the deep reservoir was not sufficient enough to trigger collapse at the surface, but the eruption left a 0.56-km diameter cored-out vent in which a dome was emplaced at the end of stage II. Petrologic evidence suggests that the stage I magma interacted with and remobilized a shallow crystal mush (∼4-6 km) that erupted during stage II and III. As the crystal mush erupted from the shallow reservoir, depressurization led to incremental subsidence of the non-coherent collapse structure. As the stage III eruption waned, local pressure release caused subsidence of the dome. Our findings highlight the importance of a connected magma reservoir, the complexity of the plumbing system, and the pattern of underpressure in controlling the nature of collapse during explosive eruptions. Huaynaputina shows that some major explosive eruptions are not always associated with caldera collapse.

Stress evolution during caldera collapse

“…Geyer et al, 2006;Roche and Druitt, 2001), but, as noted above, it also depends on the moduli of both reservoir and host rock. This effect of T/D helps explain why large eruptions from deep reservoirs may occur without resulting in collapse at surface (Lavallee et al, 2006).…”

Multidisciplinary approach of the hyperarid desert of Pampas de La Joya in southern Peru as a new Mars-like soil analog

“…It rises 5820 m above sea level, and is located just 18 km northeast from downtown Arequipa, the second largest city in Perú where over one million people live on the flanks of this extremely dangerous volcano. In fact, the hilly desert landscape south of Arequipa underlain by granitic rocks of La Caldera batholith is characterized by the presence of a discontinuous blanket of white sand (volcanic ashes) derived from the ultraplinian eruption of the Huaynaputina volcano located about 90 km east of Arequipa, which occurred in 1600 A.D. (Lavalée et al, 2006). Almost 9 km 3 of ash was generated and distributed over more than 300,000 km 2 of southern and central Perú .…”

A proximal record of caldera-forming eruptions: the stratigraphy, eruptive history and collapse of the Palaeogene Arran caldera, western Scotland

“…Smith and Kokelaar 2013). Together, these data suggest that although deposition occurred rapidly, caldera subsidence was relatively incremental and piston-like and that eruption of high-grade ignimbrites can occur without catastrophic collapse (see also Lavallée et al 2006). In eruption hiatuses, however, subsidence continued and exotic material was introduced from outside the caldera by sedimentary processes.…”