Hybrid rhyolitic eruption at Big Glass Mountain, CA, USA

Eruptive dynamics of the 1060 CE rhyolitic eruption of Big Glass Mountain (BGM), USA, are investigated with field observations, hydrogen isotope and H2O content analysis of pyroclastic obsidian chips and lavas. Field relations at BGM reveal evidence for hybrid eruption, defined as synchronous explosive venting and effusive emplacement of vast obsidian lava flows. This activity is particularly well manifested by extensive breccia zones implanted within the BGM obsidian lavas, which may represent rafted tephra cones, in addition to remnants of airfall tephra on the lava. Rhyolitic obsidians collected from a 2.5-m-thick fall deposit and co-eruptive lava flow were studied by FTIR and TCEA methods to elucidate the eruption’s degassing history. The data, along with VolcDeGas program simulations, demonstrate a correlation between H2O content and H-isotopic composition (δD) that likely reflects ever-increasing amounts of volatile loss via repetitive close-system steps, best described as batched degassing.

Forecasting the dispersion and fallout of volcanic ash during a crisis: Assessment of the September 20, 2020 eruption at Sangay volcano in Ecuador

<p>Sangay volcano (2.00°S, 78.34°W, 5326 m asl), located at the southern end of the Northern Volcanic Zone of the Andes (Morona Santiago province, Ecuador), has frequently been referred as one of the most active volcanoes in the world. Its most recent eruptive period began on May 7, 2019 and is still ongoing. It is characterized by a semi-continuous viscous lava flow emission accompanied by frequent low magnitude explosions (Vasconez et al., this meeting). This eruptive episode is the first in more than two decades to produce significant impacts both locally and regionally, and reached its paroxysm on September 20, 2020 without clear precursory signals. The eruption started at 9:20 (UTC) and lasted about one and a half hours. The eruptive column rapidly split into a high-altitude (15 km asl) gas-rich cloud, drifting eastward at 5-8 m/s and a lower (12 km asl) ash-rich cloud, drifting westward at 10-14 m/s. The ash began to fall at 11:00 (UTC) in the communities near the volcano and reached the city of Guayaquil, the second largest city in Ecuador, at 13:00 (UTC), forcing the closure of the international airport.</p><p>In this work, we evaluate the ash dispersion simulations performed by the IG-EPN using the Ash3D model before, during and after the eruption using different eruptive source parameters (ESP), by comparison with the available satellite images (GOES-16). The simulated ash fallout for each set of ESP is compared to reports from the community and volcanic observers, as well as with a fallout map obtained from a four-days field trip initiated immediately after the eruption to ensure good quality of samples and measurements (September 20-23). Ash fallout was estimated using thickness measurements where possible and area density at 40 sites located between 30 and 180 km from the volcano. The grain size distribution of 35 samples was obtained by laser diffraction.</p><p>Our results show that the general westward direction and speed of the ash cloud in the simulations is coherent with the satellite images, except for the high-altitude, gas-rich cloud. However, large discrepancies were found when comparing the simulated and measured ash fallout. Field data shows that the first simulation using ESP based on the previous activity at Sangay, underestimated the eruption size, while the second simulation using the eruption column height estimated in near-real time overestimated it. As expected, the simulation carried out immediately after the eruption, based on the first field results shows the best correlation with field data, although there are still some second-order discrepancies. In particular, the plume axis was shifted about 12° northward in the simulation, which is attributed to the atmospheric model. We also noted that the deposition pattern was slightly different between the field data and the simulation. Grain size analysis reveals uni- to multimodal distributions, associated with complex eruptive dynamics and aggregation that probably influenced the sedimentation process. Further research is needed to better understand the eruptive dynamics at Sangay in order to improve forecasts.</p>

Long-term gas observations track the early unrest phases of open-vent basaltic volcanoes

<p align="justify"><span>At open-vent basaltic volcanoes, resolving the activity escalation that heralds larger, potentially harmful eruptions is challenged by the persistent mild ordinary activity, which often masks the precursory unrest signals related to heightened magma transport from depth. Gas (SO</span><sub><span>2</span></sub><span> and CO</span><sub><span>2</span></sub><span>) fluxes at surface are controlled by rate of magma transport and degassing within the magma plumbing system, and thus constitute key parameters to infer deep magma budget and dynamics. </span></p><p align="justify"><span>Here, we use several year-long (2014-present) gas observations at Etna and Stromboli volcanoes, in Sicily, to provide new evidence for the utility of long-term instrumental gas monitoring in real-time detecting the early phase of unrest prior eruption, and for characterizing syn-eruptive dynamics. To this aim, we use information from a gas monitoring network </span>of<span> permanent ultraviolet (UV) cameras and automatic Multi-Gas instruments that, combined with geophysical observations, allow characterizing changes in degassing and eruptive dynamics at high temporal/spatial resolution. </span></p><p align="justify"><span>Our results show that the </span><span>paroxysmal (lava fountaining) explosions that periodically</span> <span>interrupted </span><span>persistent</span><span> open-vent activity on Etna (during 2014-2020) were accompanied by systematic, repetitive SO</span><sub><span>2</span></sub><span> emission patterns prior, during, and after eruptions. These allow us identifying the characteristic pre- syn- and post- eruptive degassing regimes, and to establish thresholds in the SO</span><sub><span>2</span></sub><span> flux record that mark phases of unrest. </span></p><p align="justify"><span>On Stromboli, the much improved temporal/spatial resolution of UV cameras allows resolving the escalation of regular strombolian activity, and its concentration toward its North-east crater, that heralds onset of effusive eruptions. During effusive eruption, although magma level drops in the conduit and explosive summit activity ceases, UV camera observations can still detect explosive gas bursts deep in the conduit while no infrasonic activity is detected. </span>Combining the<span> UV camera-derived SO</span><sub><span>2</span></sub><span> fluxes with CO</span><sub><span>2</span></sub><span>/SO</span><sub><span>2</span></sub><span> ratio records measured by the Multi-Gas, the CO</span><sub><span>2</span></sub><span> flux can be inferred. We find that such CO</span><sub><span>2</span></sub><span> flux time-series can allow tracking degassing of deeply stored mafic magma months before Stromboli’s eruptions. We finally show that remotely sensed gas emission and thermal activity can be combined together to characterize the dynamics of shallow magmatic system prior to and during unrest, ultimately helping to define timing of magma re-charging events driving the eruptions. </span></p>

Chapter 6.1 Marine record of Antarctic volcanism from drill cores

We review here data and information on Antarctic volcanism resulting from recent tephrostratigraphic investigations on marine cores. Records include deep drill cores recovered during oceanographic expeditions: DSDP, ODP and IODP drill cores recovered during ice-based and land-based international cooperative drilling programmes DVDP 15, MSSTS-1, CIROS-1 and CIROS-2, DVDP 15, CRP-1, CRP-2/2A and CRP-3, ANDRILL-MIS and ANDRILL-SMS, and shallow gravity and piston cores recovered in the Antarctic and sub-Antarctic oceans. We report on the identification of visible volcaniclastic horizons and, in particular, of primary tephra within the marine sequences. Where available, the results of analyses carried out on these products are presented. The volcanic material identified differs in its nature, composition and emplacement mechanisms. It was derived from different sources on the Antarctic continent and was emplaced over a wide time span.Marine sediments contain a more complete record of the explosive activity from Antarctic volcanoes and are complementary to those obtained by land-based studies. This record provides important information for volcanological reconstructions including approximate intensities and magnitudes of eruptions, and their duration, age and recurrence, as well as their eruptive dynamics. In addition, characterized tephra layers represent an invaluable chronological tool essential in establishing correlations between different archives and in synchronizing climate records.