The size and frequency of the largest explosive eruptions on Earth

Abstract

A compilation and analysis of the size and frequency of the largest known explosive eruptions on Earth are presented. The 'largest' explosive events are defined to be those eruptions yielding greater than 10 15 kg of products (>150 times the mass of the 1991 eruption of Mt. Pinatubo). This includes all known eruptions with a volcanic explosivity index (VEI) of 8. A total of 47 such events, ranging in age from Ordovician to Pleistocene, are identified, of which 42 eruptions are known from the past 36 Ma. A logarithmic 'magnitude' scale of eruption size is applied, based on erupted mass, to these events. On this scale, 46 eruptions >10 15 kg are defined to be of magnitude M8. There is one M9 event known so far, the Fish Canyon Tuff, with an erupted mass of >10 16 kg and a magnitude of 9.2. Analysis of this dataset indicates that eruptions of size M8 and larger have occurred with a minimum frequency of %1.4 events/Ma in two pulses over the past 36 Ma. On the basis of the activity during the past 13.5 Ma, there is at least a 75% probability of a M8 eruption (>10 15 kg) occurring within the next 1 Ma. There is a 1% chance of an eruption of this scale in the next 460-7,200 years. While the effect of any individual M8 or larger eruption is considerable, the time-averaged impact (i.e., erupted massfrequency) of the very largest eruptions is small, due to their rarity. The long-term, timeaveraged erupted mass flux from magnitude 8 and 9 eruptions is~10-100 times less than for M7 eruptions; the time-averaged mass eruption rate from M7 eruptions is 9,500 kg s 1 , whereas for M8 and M9 eruptions it is~70-1,000 kg s 1 . Comparison of the energy release by volcanic eruptions with that due to asteroid impacts suggests that on timescales of <100,000 years, explosive volcanic eruptions are considerably more frequent than impacts of similar energy yield. This has important implications for understanding the risk of extreme events.

Nuevos antecedentes sobre la estructura interna de la caldera La Pacana mediante un estudio gravimétrico (Andes centrales, Chile).

“…The mass of the outflow and the caldera infill is ∼1.02-1.05*10 15 , thus yielding an average VEI for both ignimbrites of ∼8, a figure slightly smaller than the Mason et al (2004) calculation for the Atana eruption, but anyway one of the largest in the world. We note that Mason et al (2004) interpreted their VEI as being produced by the single eruption of Atana ignimbrite, while our calculation considers all the erupted products regardless of the eruption. This discrepancy can also be explained by the smaller density values used in this work (1,900 kg/m 3 ) while Mason et al (2004) used larger values (2,200 -2,400 kg/m 3 ), thus yielding different estimates.…”

“…The final volume of the caldera infill and outflow resulting from these estimates is ∼3,400-3,500 km 3 , larger than by Lindsay et al (2001a) and de Silva and Gosnold (2007) for the combined Pujsa, Toconao and Atana ignimbrites (∼2,800 km 3 ). Thus, the resulting volume of the PC and PS calderas makes them some of the largest in the world, comparable to Yellowstone, Toba and La Garita (Mason et al, 2004). Assuming a vesicularity of 35% (Lindsay et al, 2001a), the ignimbrites DRE (dense rock equivalent) is ∼2,200-2,300 km 3 .…”

“…The volume estimation of old eruptions as in the APVC is a nontrivial task due to the lack of dissection that hampers estimation of the ignimbrites' thicknesses and the petrological similarity of ignimbrites erupted from different calderas. This calculation is based on simple assumptions such that the intracaldera and outf low volume deposits are approximately equal; therefore the volumes are only order of magnitude estimates (e.g., Mason et al, 2004). These assumptions do not hold for the APVC calderas (Salisbury et al, 2011).…”

“…Resurgent calderas, also known as supervolcanoes, are the result of the largest volcanic eruptions on the geological record, which have been at least two orders of magnitude bigger than any eruption ever registered by humans (e.g., Newhall and Self, 1982;Mason et al, 2004;Miller and Wark, 2008). The large size of these eruptions (volumes larger than 450 km 3 and a Volcanic Explosivity Index (VEI) greater than 8) has attracted a growing global interest to understand the evolution and eruptive dynamics of the biggest calderas (Wilson, 2008), by studying their emitted products and the formation of their structure and geometry (Sparks et al, 2005;Acocella, 2007;Martí et al, 2008;Hardy, 2008).…”

“…In this work, we present a gravimetric study of the inner structure of La Pacana, the largest caldera in the Altiplano Puna Volcanic Complex (e.g., Gardeweg and Ramírez, 1987;De Silva, 1989a, b), which produced the fifth largest eruption ever registered in the geological record (e.g., Mason et al, 2004). Despite its size and importance, the existing geological studies (Gardeweg and Ramírez, 1987;Lindsay et al, 2001a, b) have several discrepancies regarding caldera limits, intra caldera ignimbrite thicknesses, collapse geometries and erupted volumes.…”