The giant pumice (GP) preserved within lake sediments of the Toba Caldera represents post-YTT (Youngest Toba Tuff) activity and occurs as large clasts (>1 m). These pumices display jointed, hyaloclastite, and brecciated textures, and contain plagioclase, orthopyroxene, amphibole, and oxides. The GP shares geochemical and textural features with the YtD of the 74 ka YTT, including low matrix-glass SiO2, moderate to high Ba and Sr, low Y, absence of quartz and sanidine, and plagioclase with hollow textures. However, GP also displays distinguishing characteristics, notably the absence of biotite, simpler textures in amphibole and orthopyroxene, and lower Na2O + K2O and higher FeO in the matrix glass. These data suggest that GP represents a remnant of YtD magma that underwent reheating, modifying its chemical and textural signatures. Thermobarometry based on amphibole indicates magma storage at 127-289 MPa (+/- 21 MPa) and temperatures of 792-913 degrees C (+/- 22 degrees C). Despite high bulk-vesicularity and matrix-vesicle number densities (10(14)-10(15) m(-3)), GP formed through effusive, subaqueous eruptions following extensive degassing. Pheno-vesicularity data from the clast margin show minimal H2O exsolution (similar to 0.05 wt%), yet the drop from 5.9 wt% H2O to 4.3 wt% H2O implies similar to 1.6 wt% H2O should have been exsolved and recorded in the pheno-vesicularity if no outgassing during magma ascent. Interconnected vesicles and ruptured bubbles indicate that permeable gas escape occurred through shear-induced and collapse-related fracturing. After fragmentation, the margins quenched rapidly upon contact with lake water, preserving their lower vesicularity. Then a rigid outer shell formed, restricting additional gas loss and allowing the interior to retain more volatiles, producing its higher vesicularity.

Supervolcanoes like Toba Caldera, Sumatra, produce the largest eruptions on Earth. However, the magmatic conditions and processes during the period of recovery after catastrophic supereruptions, known as resurgence, are poorly understood. Here we use Bayesian statistical analysis and inverse thermal history modelling of feldspar argon-argon and zircon uranium-thorium/helium ages to investigate resurgence after the 74-thousand-year-old Youngest Toba Tuff eruption. We identify a discordance of up to around 13.6 thousand years between older feldspar and younger zircon ages. Our modelling suggests cold storage of feldspar antecrysts prior to eruption for a maximum duration of around 5 and 13 thousand years at between 280 °C and 500 °C. We propose that the solidified carapace of remnant magma after the Youngest Toba Tuff eruption erupted in a subsolidus state, without being thermally remobilized or rejuvenated. Our study indicates that resurgent uplift and volcanism initiated approximately 5 thousand years after the climactic caldera forming supereruption.

Quaternary Research is an international journal devoted to the advancement of the interdisciplinary understanding of the Quaternary Period.We aim to publish articles of broad interest with relevance to more than one discipline, and that constitute a signifi cant new contribution to Quaternary science.

Approximately 74 ka, Toba caldera in Sumatra, Indonesia, erupted in one of the most catastrophic supereruptions in Earth's history. Resurgent uplift of the caldera floor raised Samosir Island 700 m above Lake Toba, exposing valuable lake sediments. To constrain sediment chronology, we collected 173 discrete paleomagnetic 8 cm(3) cubes and 15 radiocarbon samples from six sections across the island. Bulk organic C-14 ages provide an initial chronostratigraphic framework ranging from similar to 12 to 46 ka. Natural and laboratory magnetizations were studied using alternating field demagnetization. A generally well-defined primary magnetization is isolated using principal component analysis. Comparison of inclination, and to a lesser degree declination, across independently dated sections suggests paleomagnetic secular variation (PSV) is recorded. Average inclination of -6 degrees is more negative than a geocentric axial dipole would predict, but consistent with an eastward extension of the negative inclination anomaly observed in the western equatorial Pacific. The C-14- and PSV-derived age model constrains resurgent uplift, confirming faster uplift rates to the east and slower rates to the west, while suggesting that fault blocks moved differentially from each other within a generally trapdoor-type configuration.

Large explosive eruptions of dacitic magmas, their relationship with their basaltic parent and their conditions of transfer and crystallization are widely debated. Here we report new timing constraints and a detailed study of the mineralogy and chemistry of magmas erupted over the last similar to 12 kyr at the Rinjani-Samalas volcanic complex on Lombok, in the Lesser Sunda arc. Rinjani-Samalas products define a calc-alkaline series, moderately rich in K2O. High-alumina basalts (HABs) evolved towards trachydacites (50 to similar to 68 wt % SiO2) mainly by fractional crystallization, and required the peritectic formation of (cryptic) amphibole. The pre-caldera stage is characterized by chemical bimodality (basalt-trachydacite) of the erupted magmas. Conversely, the post-caldera magmatism produced basaltic andesites. These present-day magmas possibly result from the mixing between basalt and trachydacite melts, in main proportions 0 center dot 7:0 center dot 3, before crystallization. The ad 1257 caldera-forming eruption delivered a large volume of chemically homogeneous trachydacitic magma. Its mineral paragenesis typically consists of plagioclase showing a bimodal distribution with patchy zoned cores (An(82-75)) surrounded by bands of An(50) to An(43), in association with amphibole (magnesio-hastingsite), orthopyroxene (Mg# 0 center dot 66-0 center dot 73), titanomagnetite, iron sulfide and apatite. Rare extremely calcic plagioclase (An(91-92)) records the early stage of crystallization. Extensive Mg diffusion demonstrates an overall re-equilibration of plagioclase compositions with a trachydacitic melt in equilibrium with plagioclase An(50 +/- 1) (312 +/- 42 ppm Mg). Discrepancies between the crystallization temperature of plagioclase (similar to An(50)) measured on melt inclusions (989 +/- 10A degrees C) and those provided by geothermometers (in the range between 895 and 980A degrees C) bring evidence of heterogeneity in both the temperature and the water content of the trachydacitic magma batches. Trace element geochemistry and mineralogy of bulk-rocks and volatile contents of melt inclusions suggest that the HABs initially crystallized in the lower crust; trachydacite magma batches were then extracted, transferred to shallow depths, and crystallized under conditions of water-saturation. Extensive stratigraphic data and new radiocarbon ages reveal that explosive and effusive emissions of trachydacitic magmas and strongly explosive eruptions of HABs occurred contemporaneously before the caldera-forming eruption. This implies a transfer of basaltic magma through dykes independently of the central system, a feature ascribed to the interplay between edifice mass loading, magma buoyancy and possibly the regional tectonic stress field.

Large calderas, or supervolcanoes, are sites of the most catastrophic and hazardous events on Earth, yet the temporal details of post-supereruption activity, or resurgence, remain largely unknown, limiting our ability to understand how supervolcanoes work and address their hazards. Toba Caldera, Indonesia, caused the greatest volcanic catastrophe of the last 100 kyr, climactically erupting ∼74 ka. Since the supereruption, Toba has been in a state of resurgence but its magmatic and uplift history has remained unclear. Here we reveal that new 14C, zircon U-Th crystallization and (U-Th)/He ages show resurgence commenced at 69.7±4.5 ka and continued until at least ∼2.7 ka, progressing westward across the caldera, as reflected by post-caldera effusive lava eruptions and uplifted lake sediment. The major stratovolcano north of Toba, Sinabung, shows strong geochemical kinship with Toba, and zircons from recent eruption products suggest Toba's climactic magma reservoir extends beneath Sinabung and is being tapped during eruptions.

Chemical and isotopic compositions of magmatic crystals provide important information to distinguish between deep juvenile and crustal contributions. In this work, high-resolution multicollector secondary ion mass spectrometry data reveal strong variations of δ18O values in three plagioclase crystals (800–1700μm) from two representative basaltic andesite samples of the 2010 Merapi eruption (Central Java, Indonesia). The δ18O values (from 4.6‰ to 7.9‰) are interpreted to reflect oxygen isotope heterogeneity in the melt composition during plagioclase growth. The lowest δ18O values (4.6–6.6‰) are found in anorthite-rich cores (An82–97), whereas higher δ18O values (5.7–7.9‰) are found in anorthite-poorer zones (An33–86), typically in crystal rims. Combining these new plagioclase δ18O data with δ18O of calc-silicate crustal xenoliths erupted between 1994 and 1998, the composition of glass inclusions hosted by the anorthite-rich plagioclase (An82–92), available experimental data, and the results of thermodynamic modeling using the Magma Chamber Simulator code, we conclude that the abundant anorthite-rich cores crystallized from a mantle-derived hydrous basaltic to basaltic trachyandesite melt that recharged a deeper (200–600MPa) magma storage zone, whereas lower anorthite zones crystallized at shallower levels (100–200MPa). The oxygen isotope variations in the plagioclase are explained by a two-stage model of interaction of the hydrous, mafic mantle-derived magma (1) with old crustal rocks depleted in 18O due to high temperature alteration that yielded the low δ18O values in the anorthite-rich cores at deep levels (13–20km), and later (2) with 18O-enriched carbonate material that yielded the high δ18O values in anorthite-poorer zones at shallow levels (∼4.5–9km). Thermodynamic modeling is consistent with ∼18wt.% assimilation of crustal calc-silicate material at 925–950°C and 100–200MPa by the 2010 Merapi basaltic andesite magma prior to eruption. Timescales for plagioclase phenocryst growth and residence in the magmatic plumbing system are ⩽34years. The combined data thus reveal efficient magma recharge and crustal assimilation processes that characterize the open-system magma storage and transport systems associated with the 2010 Merapi eruption.

Large explosive eruptions inject volcanic gases and fine ash to stratospheric altitudes, contributing to global cooling at the Earth’s surface and occasionally to ozone depletion. The modelling of the climate response to these strong injections of volatiles commonly relies on ice-core records of volcanic sulphate aerosols. Here we use an independent geochemical approach which demonstrates that the great 1257 eruption of Samalas (Lombok, Indonesia) released enough sulphur and halogen gases into the stratosphere to produce the reported global cooling during the second half of the 13th century, as well as potential substantial ozone destruction. Major, trace and volatile element compositions of eruptive products recording the magmatic differentiation processes leading to the 1257 eruption indicate that Mt Samalas released 158 ± 12 Tg of sulphur dioxide, 227 ± 18 Tg of chlorine and a maximum of 1.3 ± 0.3 Tg of bromine. These emissions stand as the greatest volcanogenic gas injection of the Common Era. Our findings not only provide robust constraints for the modelling of the combined impact of sulphur and halogens on stratosphere chemistry of the largest eruption of the last millennium, but also develop a methodology to better quantify the degassing budgets of explosive eruptions of all magnitudes.

New data reveal details of the post-caldera history at the Earth’s youngest resurgent supervolcano, Toba caldera in Sumatra. Resurgence after the caldera-forming ~74 ka Youngest Toba Tuff eruption uplifted the caldera floor as a resurgent dome, Samosir Island, capped with 100m of lake sediments. 14C age data from the uppermost datable sediments reveal that Samosir Island was submerged beneath lake level (~900m a.s.l) ~33.7 ky. Since then, Samosir experienced 700m of uplift as a tilted block dipping to the west. Using 14C ages and elevations of sediment along a transect of Samosir reveal that minimum uplift rates were ~4.9 cm/yr from ~33.7 to 22.5 ka, but diminished to ~0.7 cm/yr after 22.5ka. Thermo-mechanical models informed by these rates reveal that detumescence does not produce the uplift nor the uplift rates estimated for Samosir. However, models calculating the effect of volume change of the magma reservoir within a temperature-dependent viscoelastic host rock reveal that a single pulse of ~475 km3 of magma produces a better fit to the uplift data than a constant flux. Reproducing the uplift rates require more sophisticated models. Motivation for resurgent uplift of the caldera floor is rebound of remnant magma as the system re-established magmastatic and isostatic equilibrium after the caldera collapse. Previous assertions that the caldera floor was apparently at 400m a.s.l or lower requires that uplift must have initiated between sometime between 33.7 ka and 74 ka at a minimum average uplift rate of ~1.1 cm/ year. The change in uplift rate from pre-33.7 ka to immediately post-33.7 ka suggests a role for deep recharge augmenting rebound. Average minimum rates of resurgent uplift at Toba are at least an order of magnitude slower than net rates of restlessness at currently active calderas. This connotes a distinction between resurgence and restlessness controlled by different processes, scales of process, and controlling variables.