ALBERT

Description: In tectonic settings where decompression melting drives magmatism, there is compelling evidence that changes in ice loading or water loading across glacial-interglacial cycles modulate volcanic activity. In contrast, the response of subduction-related volcanoes remains unclear. A high-resolution postglacial eruption record from a large Chilean stratovolcano, Mocho-Choshuenco, provides new insight into the arc magmatic response to ice-load removal. Following deglaciation, we identify three distinct phases of activity characterized by different eruptive fluxes, sizes, and magma compositions. Phase 1 (13–8.2 ka) was dominated by large dacitic and rhyolitic explosive eruptions. During phase 2 (7.3–2.9 ka), eruptive fluxes were lower and dominated by moderate-scale basaltic andesite eruptions. Since 2.4 ka (phase 3), eruptive fluxes have been elevated and of more intermediate magmas. We suggest that this time-varying behavior reflects changes in magma storage time scales, modulated by the changing crustal stress field. During glaciation, magma stalls and differentiates to form large, evolved crustal reservoirs. Following glacial unloading, much of the stored magma erupts (phase 1). Subsequently, less-differentiated magma infiltrates the shallow crust (phase 2). As storage time scales increase, volcanism returns to more evolved compositions (phase 3). Data from other Chilean volcanoes show a similar tripartite pattern of evacuation, relaxation, and recovery, suggesting that this could be a general feature of previously glaciated arc volcanoes.

Description: In volcanically and seismically active rift systems, preexisting faults may control the rise and eruption of magma, and direct the flow of hydrothermal fluids and gas in the subsurface. Using high-resolution airborne imagery, field observations, and CO 2 degassing data on Aluto, a typical young silicic volcano in the Main Ethiopian Rift, we explore how preexisting tectonic and volcanic structures control fluid pathways and spatial patterns of volcanism, hydrothermal alteration and degassing. A new light detection and ranging (lidar) digital elevation model and evidence from deep geothermal wells show that the Aluto volcanic complex is dissected by rift-related extensional faults with throws of 50–100 m. Mapping of volcanic vent distributions reveals a structural control by either rift-aligned faults or an elliptical caldera ring fracture. Soil-gas CO 2 degassing surveys show elevated fluxes (〉〉100 g m –2 d –1 ) along major faults and volcanic structures, but significant variations in CO 2 flux along the fault zones reflect differences in near-surface permeability caused by changes in topography and surface lithology. The CO 2 emission from an active geothermal area adjacent to the major fault scarp of Aluto amounted to ~60 t d –1 ; we estimate the total CO 2 emission from Aluto to be 250–500 t d –1 . Preexisting volcanic and tectonic structures have played a key role in the development of the Aluto volcanic complex and continue to facilitate the expulsion of gases and geothermal fluids. This case study emphasizes the importance of structural mapping on active rift volcanoes to understand the geothermal field as well as potential volcanic hazards.

Description: Large igneous provinces (LIPs) are proposed to have caused a number of episodes of abrupt environmental change by increasing atmospheric CO 2 levels, which were subsequently alleviated by drawdown of CO 2 via enhanced continental weathering and burial of organic matter. Here the sedimentary records of two such episodes of environmental change, the Toarcian oceanic anoxic event (T-OAE) and preceding Pliensbachian–Toarcian (Pl-To) event (both possibly linked to the Karoo-Ferrar LIP), are investigated using a new suite of geochemical proxies that have not been previously compared. Stratigraphic variations in osmium isotope ( 187 Os/ 188 Os) records are compared with those of mercury (Hg) and carbon isotopes ( 13 C) in samples from the Mochras core, Llanbedr Farm, Cardigan Bay Basin, Wales. These sedimentary rocks are confirmed as recording an open-marine setting by analysis of molybdenum/uranium enrichment trends, indicating that the Os isotope record in these samples reflects the isotopic composition of the global ocean. The Os isotope data include the first results across the Pl-To boundary, when seawater 187 Os/ 188 Os increased from ~0.40 to ~0.53, in addition to new data that show elevated 187 Os/ 188 Os (from ~0.42 to ~0.68) during the T-OAE. Both increases in 187 Os/ 188 Os correlate with negative carbon isotope excursions and increased mercury concentrations, supporting an interplay between terrestrial volcanism, weathering, and climate that was instrumental in driving these distinct episodes of global environmental change. These observations also indicate that the environmental impact of the Karoo-Ferrar LIP was not limited solely to the T-OAE.

Description: Volcanoes are often remote, and have footprints that may extend across many hundreds or thousands of square kilometres. They are generally inaccessible during eruption, and may continue to be inaccessible for extended periods of time after eruption, while their products can be scattered or dispersed over regional or global scales. Consequently, since direct measurement can only provide us with part of the picture of many volcanic processes, remote sensing is now playing an increasingly important role in advancing understanding of the science underlying volcanic behaviour, on this planet and beyond (e.g. Mouginis-Mark et al. 2000; Sparks et al. 2012). Satellite, airborne and ground-based remote sensing are increasingly vital tools for monitoring active or potentially active volcanoes, and assessing their likely, real-time or time-averaged impact (Fig. 1). At the same time, the synoptic-scale surveys that are often well suited to remote-sensing techniques allow us to address questions about the fundamental processes that control volcano behaviour in a way that is not necessarily possible from individual case studies. New research is often driven by technological advancements in the development of novel sensors or launching of new platforms, meaning that the space agencies are increasingly involved in identifying scientific questions and priorities (e.g. Ferruci et al. 2012). Multiple and complementary data streams are increasingly being used both to monitor active volcanoes and advance volcanological science. The key geophysical parameters that comprise monitoring data streams typically include the categories of (i) seismicity, (ii) surface deformation, (iii) thermal measurements and (iv) gas flux and composition data as major components. While measurements of seismicity remain the domain of ground-based seismometers, remote-sensing techniques have made major contributions in each of the others. This Special Publication volume is concerned with the use of remote sensing at volcanoes. It is split into three parts, roughly arranged from the subsurface, to the surface, and then further afield as volcanic products are injected and dispersed into the atmosphere. The papers span a range of applications of remote-sensing techniques to monitor and understand (a) surface deformation, (b) surface thermal anomalies and (c) gas fluxes, as well as tracking ash and gas plumes from eruptions to gain insights into the extent of a volcano's impacts. Volcanology is driven, in part, by the operational concerns surrounding volcano monitoring and hazard and crisis management but the goal of volcanological science is, at its heart, to understand the processes that underlie volcanic activity. This Special Publication is also concerned with how we go from observations to this deeper understanding, including the progress that can be made by integrating observations and modelling. While this volume focuses mainly on satellite-based remote sensing, integrating datasets from different platforms is also of vital importance, and so papers on airborne remote sensing and measurement from both manned and unmanned aircraft are also included.

Description: In tectonic settings where decompression melting drives magmatism, there is compelling evidence that changes in ice loading or water loading across glacial-interglacial cycles modulate volcanic activity. In contrast, the response of subduction-related volcanoes remains unclear. A high-resolution postglacial eruption record from a large Chilean stratovolcano, Mocho-Choshuenco, provides new insight into the arc magmatic response to ice-load removal. Following deglaciation, we identify three distinct phases of activity characterized by different eruptive fluxes, sizes, and magma compositions. Phase 1 (13–8.2 ka) was dominated by large dacitic and rhyolitic explosive eruptions. During phase 2 (7.3–2.9 ka), eruptive fluxes were lower and dominated by moderate-scale basaltic andesite eruptions. Since 2.4 ka (phase 3), eruptive fluxes have been elevated and of more intermediate magmas. We suggest that this time-varying behavior reflects changes in magma storage time scales, modulated by the changing crustal stress field. During glaciation, magma stalls and differentiates to form large, evolved crustal reservoirs. Following glacial unloading, much of the stored magma erupts (phase 1). Subsequently, less-differentiated magma infiltrates the shallow crust (phase 2). As storage time scales increase, volcanism returns to more evolved compositions (phase 3). Data from other Chilean volcanoes show a similar tripartite pattern of evacuation, relaxation, and recovery, suggesting that this could be a general feature of previously glaciated arc volcanoes.

Description: The Ozone Monitoring Instrument (OMI) is a satellite-based ultraviolet (UV) spectrometer with unprecedented sensitivity to atmospheric sulphur dioxide (SO 2 ) concentrations. Since late 2004, OMI has provided a high-quality SO 2 dataset with near-continuous daily global coverage. In this review, we discuss the principal applications of this dataset to volcano monitoring: (1) the detection and tracking of large eruption clouds, primarily for aviation hazard mitigation; and (2) the use of OMI data for long-term monitoring of volcanic degassing. This latter application is relatively novel, and despite showing some promise, requires further study into a number of key uncertainties. We discuss these uncertainties, and illustrate their potential impact on volcano monitoring with OMI through four new case studies. We also discuss potential future avenues of research using OMI data, with a particular emphasis on the need for greater integration between various monitoring strategies, instruments and datasets.

Description: We investigate high-resolution digital photographs and infrared images of the lava dome eruption at Volcán de Colima, from 2007 to 2010. Qualitative observations provide insight into active volcanic processes (e.g. rockfalls and fracturing) and show that, as the dome advances a substantial cooled talus apron develops, which stabilizes the structure. Progressive collapse of the talus apron as it reaches the crater rim corresponds with the development of a lava lobe, extruding hot lava from deeper within the dome. Quantitative dome surface temperature time-series show that the highest temperature hotspots migrate from the dome sides (250–380 °C) to the top (150–300 °C) and finally to the lava lobe (220–400 °C) as the structurally unstable areas expose fresh material. Net surface heat loss from the dome ranges from 5 to 30 MW, comparable to other dome forming systems. Heat budget calculations confirm that the lava dome retained a hot viscous core throughout the period 2007–2010. We propose that the mechanical stability of the Volcán de Colima dome arises from the shear strength of flanking talus which stabilizes the hot viscous core.

Description: Sulfides are a major potential repository for magmatic metals and sulfur. In relatively reduced magmas, there may be a dynamic interplay between sulfide liquids and magma degassing as magmas ascend/erupt. Sulfide-bubble aggregates may segregate to shallow levels. Exsolved fluids may oxidize sulfides to produce SO 2 gas and metals, which can vent to the atmosphere with chalcophile metal ratios reflecting those in their parent sulfide liquids. Sulfide breakdown and/or sequestration timing and balance define the role of sulfides in both ore formation and the environmental impacts of volcanic eruptions, including during the evolution of large igneous provinces, which are key periods of heightened volcanism during Earth history.