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

Abstract

The 1963 AD eruption of Agung volcano was one of the most significant twentieth century eruptions in Indonesia, both in terms of its explosivity (volcanic explosivity index (VEI) of 4+) and its short-term climatic impact as a result of around 6.5 Mt SO2 emitted during the eruption. Because Agung has a significant potential to generate more sulphur-rich explosive eruptions in the future and in the wake of reported geophysical unrest between 2007 and 2011, we investigated the Late Holocene tephrostratigraphic record of this volcano using stratigraphic logging, and geo-chemical and geochronological analyses. We show that Agung has an average eruptive frequency of one VEI >= 2-3 eruptions per century. The Late Holocene eruptive record is dominated by basaltic andesitic eruptions generating tephra fall and pyroclastic density currents. About 25 % of eruptions are of similar or larger magnitude than the 1963 AD event, and this includes the previous eruption of 1843 AD (estimated VEI 5, contrary to previous estimations of VEI 2). The latter represents one of the chemically most evolved products (andesite) erupted at Agung. In the Late Holocene, periods of more intense explosive activity alternated with periods of background eruptive rates similar to those at other subduction zone volcanoes. All eruptive products at Agung show a texturally complex mineral assemblage, dominated by plagioclase, clinopyroxene, orthopyroxene and olivine, suggesting recurring open-system processes of magmatic differentiation. We propose that erupted magmas are the result of repeated intrusions of basaltic magmas into basaltic andesitic to andesitic reservoirs producing a hybrid of bulk basaltic andesitic composition with limited compositional variations

Using Lake Sediment Cores to Improve Records of Volcanism at Aluto Volcano in the Main Ethiopian Rift

“…In each case, these clusters include five or more consecutive eruptions with a maximum repose time of 150 years. Episodic behaviors on varying timescales have been observed in other volcanic systems and are associated with the interactions between magma evolution, ascent, degassing, and crystallization (e.g., Fontijn et al, 2015;Sheldrake et al, 2016). ka BP (Figure 8b).…”

Timing, magnitude and geochemistry of major Southeast Asian volcanic eruptions: identifying tephrochronologic markers

“…Volcanoes that frequently erupted during historical time have generally been more studied, e.g. Merapi (Andreastuti et al, 2000;Gertisser and Keller, 2003;Jousset et al, 2013 and references therein), Krakatau (Self and Rampino, 1981;Rampino and Self, 1982;Camus et al, 1987;Dahren et al, 2012), Kelut (Zen and Hadikusumo, 1965;Bourdier et al, 2002;Jeffery et al, 2013;Kristiansen et al, 2015;Maeno et al, 2017), Agung (Rampino and Self, 1982;Self and Rampino, 2012;Fontijn et al, 2015), Taal (Delos Reyes et al, 2018 and references therein), or Mayon (Moore and Melson, 1969;Newhall, 1979;Castillo and Newhall, 2004). People remember large eruptions well for decades to centuries, e.g.…”

“…Devine et al, 1984;Foden, 1986;Wheller et al, 1987;Mandeville et al, 1996;Rutherford and Devine, 1996;Chesner, 1998;Turner and Foden, 2001;Reubi and Nicholls, 2005). Unfortunately, there are few publications relating to local or regional tephrostratigraphy due to the often difficult access to samples: limitations of proximal stratigraphical studies to the past 3000-5000 years, older deposits being buried (Andreastuti et al, 2000;Fontijn et al, 2015), continual changes in land use in this very densely populated region, and poorer ash preservation potential given the equatorial climate with high mean annual precipitation, frequent lahars and landslides (Kirschbaum et al, 2010;Petley, 2010). Nevertheless, some tephrochronologic markers have been identified and used, such as the tuffs from the Toba caldera (e.g.…”

Tephra without Borders: Far-Reaching Clues into Past Explosive Eruptions

“…Geochemical time-series studies on timescales of months to thousands of years typically address eruptive histories and magmatic evolution of individual volcanoes and mostly focus on proximal terrestrial tephra sequences (e.g., Smith et al, 2005Smith et al, , 2011aDonoghue et al, 2007;Óladóttir et al, 2008Hasegawa et al, 2011;Turner et al, 2011;Firth et al, 2014;Iverson et al, 2014;Schindlbeck et al, 2014;Fontijn et al, 2015;Ponomareva et al, 2015). On a longer time scale (thousands to millions of years), tephras are more readily preserved in nonerosive marine environments that are relatively close to active volcanoes.…”