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Large igneous provinces (LIPs) represent some of the greatest volcanic events in Earth history with significant impacts on ecosystems, including mass extinctions. However, some fundamental questions related to the eruption rate, eruption style, and vent locations for LIP lava flows remain unanswered. In this review, we use the Cretaceous–Paleogene Deccan Traps as an archetype to address these questions because they are one of the best-preserved large continental flood basalt provinces. We describe the volcanological features of the Deccan flows and the potential temporal and regional variations as well as the spatial characteristics of potential feeder dikes. Along with estimates of mean long-term eruption rates for individual Deccan lavas from paleomagnetism and Hg proxy records of ∼50–250 km3/year (erupting for tens to hundreds of years), the Deccan volcanic characteristics suggest a unified conceptual model for eruption of voluminous (>1,000 km3) LIP lavas with large spatial extent (>40,000 km2). We conclude by highlighting a few key open questions and challenges that can help improve our understanding of how the Deccan flows, as well as LIP flows in general, erupted and the mechanisms by which the lavas may have flowed over distances up to 1,000 km. ▪ The Deccan Traps are an archetype for addressing fundamental volcanological questions related to eruption rate, eruption style, and vent locations for large igneous province lava flows. ▪ Deccan subprovinces likely evolved as separate volcanic systems; thus, long-distance/interprovince flow correlations must be carefully assessed. ▪ The earliest eruptions came through the Narmada-Tapi rift zone followed by the establishment of a separate magmatic plumbing system by mantle plume–associated magmas. ▪ Typical Deccan eruption rates were ∼50–250 km3/year of lava. Individual eruptions lasted for a few hundred to 1,000 years and were separated by hiatuses of 3,000–6,000 years. ▪ The conspicuous absence of dikes in the Central Deccan region strongly implies long-distance surface transport of lavas in the form of flows hundreds of kilometers long.

International audience; Volcano sector collapses are catastrophic events that can mobilize huge volumes of material and cause changes in the magmatic plumbing system, leading to variations in growth rate and/or composition. Dating pre-historic volcanic debris avalanche deposits is challenging. Geological materials directly recording avalanche formation and amenable to radiometric dating are rare, and, in the case of Holocene events, the applicable radiometric dating techniques are scarce. Socompa volcano suffered the largest collapse event in the Central Volcanic Zone of the Andes, producing one of Earth's most spectacular and best-preserved volcano avalanche deposits. We apply multiple dating techniques to unravel the timing of Socompa's collapse and gain insights into its pre- and post-collapse eruptive history. The age of the collapse event is constrained by a 14C age of 6,200-6,400 BP of a paleosol buried by the avalanche, and by a post-collapse lava flow dated at 5.91 ± 0.43 ka by zircon double-dating. Bayesian age sequence modeling integrating these ages determines that the collapse occurred at 6.18-0.64+0.28 ka. Four zircon eruption dates and one unspiked K-Ar age between 69.2 ± 6.0 and 22.1 ± 1.9 ka constrain the age of the youngest stage of activity before the collapse. The ages, together with paleosurface modeling and volume calculations, allow estimating growth rates for the young pre-collapse and post-collapse stages of ~ 0.2-0.3 km3/kyr and ~ 0.5-2 km3/kyr, respectively, indicating a significant increase in activity after the collapse event. The collapse may have triggered a new growth phase or accelerated an ongoing one and was likely associated with a Plinian eruption that produced widespread pumice fallout. The pre- and post-collapse lavas have similar compositions and zircon crystallization age distributions, suggesting that the same or a similar magma reservoir was tapped before and after the collapse. Thus, huge collapses such as Socompa's event can promote increased volcanic activity as a consequence of the unloading effect, but the overall plumbing system may not be affected enough to show significant variations in erupted compositions, at least transiently. Our results highlight the efficacy of the zircon double-dating method for dating very young felsic lavas and for constraining the age of debris avalanche deposits. This is particularly relevant in the Andean Central Volcanic Zone and other regions with arid climates, where organic material is rare and hence 14C dating is often unfeasible. Furthermore, the post-collapse zircon eruption age of 5.91 ± 0.43 ka is the youngest radiometric age yet obtained for a lava flow in the southern Central Volcanic Zone, highlighting the youth of volcanic activity at Socompa, and confirming its status as a Holocene active volcano.

Columnar structures have been exposed by preferential weathering in non-welded, non-vapor-phase-altered zones of the 1.2 to 1.8 Ma Bandelier Tuff ignimbrites around Valles Caldera, New Mexico. These long, largely vertical cylindrical features are similar in composition and texture to the host ignimbrite but represent areas that underwent alteration to make them more resistant to erosion. Analyses show that the column ignimbrite was altered by the addition of the zeolite mordenite as a mineral cement into pore spaces. This, and the presence of illite and, to a lesser extent, chlorite, suggests alteration at ~120–125°C. We map column geometry, spacing, stratigraphic location, and spatial distribution. Columns are mostly vertical, there is a correlation between the diameters and spacing, and they exist in linear to rounded clusters of a few to 30 columns. Based on the location within the ignimbrites, the shape and form of column groups, and the temperature of formation of the columns, we propose that slumping of over-steepened valley walls exposed friable, warm, unaltered ignimbrite that enabled ponded meteoritic water to permeate into the deposit, which allowed localized convective chimney cells to form. We develop an analytical model to show that infiltrating water is convectively unstable, and, for reasonable permeabilities, we can explain the observed column spacing and alteration temperature. This model permits columns to form within parts of the deposits perched in ignimbrite deposited against pre-existing valley walls. An abundant supply of water from high precipitation is implied, reflecting a syn-glacial, pluvial climate in the southwestern United States at that time (1–2 Ma ago).

The Youngest Toba Tuff (YTT) supereruption from Toba Caldera in Sumatra at ca. 74,000 years BP is the largest volcanic event recorded in the Pleistocene. Intriguingly, recent radioisotopic dating of the near antipodal Los Chocoyos (LCY) supereruption from the Atitlán caldera in Guatemala finds an identical age within uncertainties to that of YTT. This opens the question of whether these synchronous supereruptions may be a coincidence or could be a consequence of each other? Using the known eruptive record from the past 2 Myr, we find that the likelihood of having two near antipodal supereruptions (>1,000 km3 tephra volume) within centuries (