Variability in eruptive dynamics associated with caldera collapse: an example from two successive eruptions at Batur volcanic field, Bali, Indonesia

Abstract

Batur volcanic field (BVF) in Bali, Indonesia, underwent two successive caldera-forming eruptions, CI and CII (29,300 and 20,150 years b.p., respectively) that resulted in the deposition of dacitic ignimbrites. The respective ignimbrites show contrasted stratigraphies, exemplify the variability of dynamics associated with caldera-forming eruptions and provide insights into the possible controls exerted by caldera collapse mechanisms. The Ubud Ignimbrite is widespread and covers most of southern Bali. The deposits consist dominantly of pyroclastic flow with minor pumice fall deposits. The intracaldera succession comprises three distinct, partially to densely welded cooling units separated by non-welded pyroclastic flow and fall deposits. The three cooling units consist of pyroclastic flow deposits only and together represent up to 16 distinct flow units, each including a thin, basal, lithic-rich breccia. This eruption was related to a 13.510 km caldera (CI) with a minimum collapsed volume of 62 km 3 . The floor of caldera CI is inferred to have a piecemeal geometry. The Ubud Ignimbrite is interpreted as the product of a relatively long-lasting, pulsating, collapsing fountain that underwent at least two time breaks. A stable column developed during the second time break. Discharge rate was high overall, but oscillatory, and increased toward the end of the eruption. These dynamics are thought to reflect sequential collapse of the CI structure. The Gunungkawi Ignimbrite is of more limited extent outside the source caldera and occurs only in central southern Bali. The Gunungkawi Ignimbrite proximal deposits consist of interbedded accretionary lapilli-bearing ash surge, ash fall, pumice lapilli fall and thin pyroclastic flow deposits, overlain by a thick and massive pyroclastic flow deposit with a thick basal lag breccia. The caldera (CII) is 7.56 km in size, with a minimum collapsed volume of 9 km 3 . The CII eruption included two distinct phases. During the first, eruption intensity was low to moderate and an unstable, essentially phreatomagmatic column developed. During the second phase, the onset of caldera collapse drastically increased the eruption intensity, resulting in column collapse. The caldera floor is believed to have subsided rapidly, producing a single, short-lived burst of high eruption intensity that resulted in the deposition of the uppermost massive pyroclastic flow.

Double trouble: Paired ignimbrite eruptions and collateral subsidence in the Taupo Volcanic Zone, New Zealand

“…At the largest scale, multiple linked structures have been inferred for the caldera collapses associated with the 0.64 Ma Lava Creek and 2.05 Ma Huckleberry Ridge tuffs at Yellowstone (Christiansen, 1979(Christiansen, , 2001. On a smaller scale, such composite collapses ("piecemeal collapse" of Branney and Kokelaar, 1994) may be indicated by coeval eruption of diverse and independent magmas, suggesting evacuation of multiple independent chambers, such as at Whakamaru in the Taupo Volcanic Zone (Brown et al, 1998), Shikotsu in Japan (Nakagawa et al, 2003), and Batur in Bali (Reubi and Nicholls, 2004). In cases of composite collapse, the overall morphology of the caldera may be little different from that of the simple caldera (Fig.…”

The Breccia Museo formation, Campi Flegrei, southern Italy: geochronology, chemostratigraphy and relationship with the Campanian Ignimbrite eruption

“…The occurrence of proximal lithic-rich breccia emplaced during ignimbrite eruption is widely documented (e.g. Druitt and Sparks 1982;Wilson et al 1995;Milner et al 2003;Reubi and Nicholls 2004;Ponomareva et al 2004). As regards chemical composition, the diagrams of Figs.…”

A 5000-year record of multiple highly explosive mafic eruptions from Gunung Agung (Bali, Indonesia): implications for eruption frequency and volcanic hazards

“…These pumice fall deposits are usually poorly preserved, and we could only obtain geochemical data for the three most recent ones, including the one we interpret to be associated with the 1843 AD eruption (see further). There is no evidence for large Plinian-style fall or ignimbrite deposits at Agung, in contrast to Batur (Reubi and Nicholls 2004a;Sutawidjaja 2009). …”

“…on Bali, surrounded by the major calderas of Bratan (Ryu et al 2013) and Batur (Reubi and Nicholls 2004a;Sutawidjaja 2009) to the west (Fig. 1), and the Rinjani-Samalas complex (Lavigne et al 2013) on Lombok to the east.…”