Bouncing Spallation Bombs During the 2021 La Palma Eruption, Canary Islands, Spain

Incandescent pyroclasts of more than 64 mm in diameter erupted from active volcanoes are known as bombs and pose a significant hazard to life and infrastructure. Volcanic ballistic projectile hazard assessment normally considers fall as the main transport process, estimating its intensity from bomb location and impact cratering. We describe ballistically ejected bombs observed during the late October 2021 episode of eruption at La Palma (Canary Islands) that additionally travelled downhill by rolling and bouncing on the steep tephra-dominated cone. These bouncing bombs travelled for distances >1 km beyond their initial impact sites, increasing total travel distance by as much as 100%. They left multiple impact craters on their travel path and frequently spalled incandescent fragments on impact with substrate, leading to significant fire hazard for partially buried trees and structures far beyond the range of ballistic transport. We term these phenomena as bouncing spallation bombs. The official exclusion zone encompassed this hazard at La Palma, but elsewhere bouncing spallation bombs ought to be accounted for in risk assessment, necessitating awareness of an increased hazard footprint on steep-sided volcanoes with ballistic activity

The 2021 eruption of the Cumbre Vieja volcanic ridge on La Palma, Canary Islands

Almost exactly half a century after the eruption of the Teneguía Volcano on La Palma (26 October to 28 November 1971), a new eruption occurred on the island and lasted for 85 days from 19 September until 13 December 2021. This new eruption opened a volcanic vent complex on the western flank of the Cumbre Vieja rift zone, the N-S elongated polygenetic volcanic ridge that has developed on La Palma over the last c. 125 ka. The Cumbre Vieja ridge is the volcanically active region of the island and the most active one of the Canary Islands, hosting half of all the historically recorded eruptive events in the archipelago. The 2021 La Palma eruption has seen no direct loss of human life, thanks to efficient early detection and sensible management of the volcanic crisis by the authorities, but more than 2800 buildings and almost 1000 hectares of plantations and farmland were affected by lava flows and pyroclastic deposits. Satellite surveillance enabled accurate mapping of the progressive buildup of the extensive and complex basaltic lava field, which together with monitoring of gas emissions informed the timely evacuation of local populations from affected areas. Lava flows that reached the sea constructed an extensive system of lava deltas and platforms, similar to events during earlier historical eruptions such as in 1712, 1949 and 1971. Long-term challenges in the aftermath of the eruption include protection of drainage systems from potential redistribution of tephra during high rainfall events, the use of the large surplus quantities of ash in reconstruction of buildings and in agriculture, and the crucial concerns of where and how rebuilding should and could occur in the aftermath of the eruption. Finally, there remain strong financial concerns over insurance for properties consumed or damaged by the eruption in the light of future volcanic hazards from the Cumbre Vieja volcanic ridge.Peer reviewe

Trans-crustal magma storage in contrasting tectonic settings

Magmatic plumbing systems comprise magma chambers, sheet intrusions, and conduits which link the Earth’s deep interior with the Earth’s surface. As such, they are the structural framework of magma transport and storage that is governed by complex physical and chemical processes in magma reservoirs and through the interaction of magma bodies with surrounding crustal rocks over timescales from hours to millions of years. These geological processes, in turn, play a vital role in controlling eruptive behaviour and the magnitude of associated volcanic eruptions that impact the environment as well as human society. Our understanding of the nature and location of magmatic processes and plumbing system architecture remains, however, fragmentary. This lack of knowledge can partly be attributed to limits regarding the spatial resolution of geophysical methods and partly to geochemical uncertainties and errors in associated models. Ongoing advances in analytical techniques increase spatial, temporal, and chemical resolution, hence enabling us to gather more detailed knowledge on the structure and dynamics of magmatic systems, especially for individual volcanoes, but also in respect to the long-term evolution of magmatic provinces and ultimately the Earth as a whole. This process-oriented thesis examines fossil and active magmatic plumbing systems in Iceland, Indonesia, Cameroon, and the Canary Islands by applying a combination of traditional and state-of-the-art petrological and geochemical methods, mineral(-melt) thermobarometric modelling, and isotopic analytical techniques. The results add valuable insights to the growing body of evidence for multi-tiered plumbing systems in a number of volcano-tectonic settings and underline the importance of shallow-level magma storage and its influence on magma evolution and hazardous volcanic eruptions

Trans-crustal magma storage in contrasting tectonic settings

Magmatic plumbing systems comprise magma chambers, sheet intrusions, and conduits which link the Earth’s deep interior with the Earth’s surface. As such, they are the structural framework of magma transport and storage that is governed by complex physical and chemical processes in magma reservoirs and through the interaction of magma bodies with surrounding crustal rocks over timescales from hours to millions of years. These geological processes, in turn, play a vital role in controlling eruptive behaviour and the magnitude of associated volcanic eruptions that impact the environment as well as human society. Our understanding of the nature and location of magmatic processes and plumbing system architecture remains, however, fragmentary. This lack of knowledge can partly be attributed to limits regarding the spatial resolution of geophysical methods and partly to geochemical uncertainties and errors in associated models. Ongoing advances in analytical techniques increase spatial, temporal, and chemical resolution, hence enabling us to gather more detailed knowledge on the structure and dynamics of magmatic systems, especially for individual volcanoes, but also in respect to the long-term evolution of magmatic provinces and ultimately the Earth as a whole. This process-oriented thesis examines fossil and active magmatic plumbing systems in Iceland, Indonesia, Cameroon, and the Canary Islands by applying a combination of traditional and state-of-the-art petrological and geochemical methods, mineral(-melt) thermobarometric modelling, and isotopic analytical techniques. The results add valuable insights to the growing body of evidence for multi-tiered plumbing systems in a number of volcano-tectonic settings and underline the importance of shallow-level magma storage and its influence on magma evolution and hazardous volcanic eruptions

Characterising the magma supply system of Agung and Batur volcanoes on Bali, Indonesia

Volcanic and magmatic processes are controlled by the composition of the magmas involved and the nature and structure of their underlying plumbing systems. To understand and predict volcanic behaviour, it is of critical importance to characterize the associated magmatic plumbing and supply system. This study investigates the magma plumbing system beneath Bali, Indonesia by employing several thermobarometric models using mineral phases in lavas from the simultaneous eruptions of Agung and Batur volcanoes in 1963 and the 1974 eruption of Batur. Compositional data were acquired from feldspar, pyroxene, and olivine crystals, using electron microprobe analysis, as well as from whole-rock samples using inductively coupled plasma mass spectrometry. Clinopyroxene-melt and clinopyroxene composition thermobarometers were then applied to equilibrated clinopyroxene-melt couples, while plagioclase-melt thermobarometry was employed on equilibrated plagioclase-melt pairs. The results were used to construct comprehensive magmatic plumbing models for Agung and Batur and are compared with geochemical, geophysical and petrological data on these volcanoes and others in the region. For the 1963 Agung eruption, results from clinopyroxene-melt thermobarometry suggest dominant crystallisation levels between 18 and 22 km depth. Clinopyroxene from the 1963 eruption of Batur record crystallisation depths between 12 and 18 km, whereas clinopyroxene from the 1974 Batur eruption show a main crystallisation level between 15 and 19 km. Furthermore, plagioclase-melt thermobarometry indicates the existence of shallow level magma reservoirs, with depths between 3 and 7 km for the 1963 eruption of Agung, between 2 and 4 km for the 1963 Batur eruption and between 3 and 5 km for the 1974 Batur event. The deep magma storage regions notably coincide with lithological boundaries in the crust and mantle beneath Bali, while the shallow reservoirs are consistent with recent geophysical studies that point to regional shallow-level magma storage. An along-arc comparison reveals this trend to be characteristic of Sunda arc magma storage systems and highlights the utility of a thermobarometric approach to detect multi-level systems beneath recently active volcanic systems

Characterising the magma supply system of Agung and Batur volcanoes on Bali, Indonesia

Volcanic and magmatic processes are controlled by the composition of the magmas involved and the nature and structure of their underlying plumbing systems. To understand and predict volcanic behaviour, it is of critical importance to characterize the associated magmatic plumbing and supply system. This study investigates the magma plumbing system beneath Bali, Indonesia by employing several thermobarometric models using mineral phases in lavas from the simultaneous eruptions of Agung and Batur volcanoes in 1963 and the 1974 eruption of Batur. Compositional data were acquired from feldspar, pyroxene, and olivine crystals, using electron microprobe analysis, as well as from whole-rock samples using inductively coupled plasma mass spectrometry. Clinopyroxene-melt and clinopyroxene composition thermobarometers were then applied to equilibrated clinopyroxene-melt couples, while plagioclase-melt thermobarometry was employed on equilibrated plagioclase-melt pairs. The results were used to construct comprehensive magmatic plumbing models for Agung and Batur and are compared with geochemical, geophysical and petrological data on these volcanoes and others in the region. For the 1963 Agung eruption, results from clinopyroxene-melt thermobarometry suggest dominant crystallisation levels between 18 and 22 km depth. Clinopyroxene from the 1963 eruption of Batur record crystallisation depths between 12 and 18 km, whereas clinopyroxene from the 1974 Batur eruption show a main crystallisation level between 15 and 19 km. Furthermore, plagioclase-melt thermobarometry indicates the existence of shallow level magma reservoirs, with depths between 3 and 7 km for the 1963 eruption of Agung, between 2 and 4 km for the 1963 Batur eruption and between 3 and 5 km for the 1974 Batur event. The deep magma storage regions notably coincide with lithological boundaries in the crust and mantle beneath Bali, while the shallow reservoirs are consistent with recent geophysical studies that point to regional shallow-level magma storage. An along-arc comparison reveals this trend to be characteristic of Sunda arc magma storage systems and highlights the utility of a thermobarometric approach to detect multi-level systems beneath recently active volcanic systems

Characterising the magma supply system of Agung and Batur volcanoes on Bali, Indonesia

Volcanic and magmatic processes are controlled by the composition of the magmas involved and the nature and structure of their underlying plumbing systems. To understand and predict volcanic behaviour, it is of critical importance to characterize the associated magmatic plumbing and supply system. This study investigates the magma plumbing system beneath Bali, Indonesia by employing several thermobarometric models using mineral phases in lavas from the simultaneous eruptions of Agung and Batur volcanoes in 1963 and the 1974 eruption of Batur. Compositional data were acquired from feldspar, pyroxene, and olivine crystals, using electron microprobe analysis, as well as from whole-rock samples using inductively coupled plasma mass spectrometry. Clinopyroxene-melt and clinopyroxene composition thermobarometers were then applied to equilibrated clinopyroxene-melt couples, while plagioclase-melt thermobarometry was employed on equilibrated plagioclase-melt pairs. The results were used to construct comprehensive magmatic plumbing models for Agung and Batur and are compared with geochemical, geophysical and petrological data on these volcanoes and others in the region. For the 1963 Agung eruption, results from clinopyroxene-melt thermobarometry suggest dominant crystallisation levels between 18 and 22 km depth. Clinopyroxene from the 1963 eruption of Batur record crystallisation depths between 12 and 18 km, whereas clinopyroxene from the 1974 Batur eruption show a main crystallisation level between 15 and 19 km. Furthermore, plagioclase-melt thermobarometry indicates the existence of shallow level magma reservoirs, with depths between 3 and 7 km for the 1963 eruption of Agung, between 2 and 4 km for the 1963 Batur eruption and between 3 and 5 km for the 1974 Batur event. The deep magma storage regions notably coincide with lithological boundaries in the crust and mantle beneath Bali, while the shallow reservoirs are consistent with recent geophysical studies that point to regional shallow-level magma storage. An along-arc comparison reveals this trend to be characteristic of Sunda arc magma storage systems and highlights the utility of a thermobarometric approach to detect multi-level systems beneath recently active volcanic systems

Locating the depth of magma supply for volcanic eruptions, insights from Mt. Cameroon

Mt. Cameroon is one of the most active volcanoes in Africa and poses a possible threat to about half a million people in the area, yet knowledge of the volcano’s underlying magma supply system is sparse. To characterize Mt. Cameroon’s magma plumbing system, we employed mineral-melt equilibrium thermobarometry on the products of the volcano’s two most recent eruptions of 1999 and 2000. Our results suggest pre-eruptive magma storage between 20 and 39 km beneath Mt. Cameroon, which corresponds to the Moho level and below. Additionally, the 1999 eruption products reveal several shallow magma pockets between 3 and 12 km depth, which are not detected in the 2000 lavas. This implies that small-volume magma batches actively migrate through the plumbing system during repose intervals. Evolving and migrating magma parcels potentially cause temporary unrest and short-lived explosive outbursts, and may be remobilized during major eruptions that are fed from sub-Moho magma reservoirs

Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions

The island of Bali in Indonesia is home to two active stratovolcanoes, Agung and Batur, but relatively little is known of their underlying magma plumbing systems. Here we define magma storage depths and isotopic evolution of the 1963 and 1974 eruptions using mineral-melt equilibrium thermobarometry and oxygen and helium isotopes in mineral separates. Olivine crystallised from a primitive magma and has average delta O-18 values of 4.8%. Clinopyroxene records magma storage at the crust-mantle boundary, and displays mantle-like isotope values for Helium (8.62 R-A) and delta O-18 (5.0-5.8%). Plagioclase reveals crystallisation in upper crustal storage reservoirs and shows delta O-18 values of 5.5-6.4%. Our new thermobarometry and isotope data thus corroborate earlier seismic and InSAR studies that inferred upper crustal magma storage in the region. This type of multi-level plumbing architecture could drive replenishing magma to rapid volatile saturation, thus increasing the likelihood of explosive eruptions and the consequent hazard potential for the population of Bali