Wj McGuire

Correlation between rate of sea-level change and frequency of explosive volcanism in the Mediterranean

Volcanic activity has frequently been linked to Quaternary environmental change, either by driving climate modification, or in response to environmental changes. Although a link has been established between large explosive eruptions and small (0.5 °C), brief (1–2 years) falls in global temperatures, both the evidence and mechanisms responsible for longer episodes of eruption-induced planetary cooling remain questionable,,,. In contrast, recent research based on ice-core data suggests that rapid climate changes during the past 110,000 years increased explosive volcanic activity. Here we present a statistical analysis relating the frequency of explosive activity of Mediterranean volcanoes — based on dated tephra layers in deep-sea sediment cores — to the rate of late Quaternary sea-level change. The nonlinear correlation between the two is tentatively explained in terms of dynamic responses of the volcanoes to stress-related influences on various spatial scales. The correlation supports a mechanism or mechanisms by which the climate-driven growth and decay of large ice sheets can influence the eruptive chronologies of distant volcanic edifices via changes in global sea level.

Coastal elevation changes in eastern Sicily: implications for volcano instability at Mount Etna

Abstract The eastern flank of Mount Etna, Sicily has been recognized as being unstable, and three contrasting models have been proposed to account for this phenomenon, these being deep-seated spreading, shallow sliding and tectonic block movements. These models are examined by making reference to the rates and patterns of crustal movement along the eastern coastline of Sicily as determined from palaeoshoreline data. The south-eastern coastline of Sicily (Portopalo to Catania) provides no evidence of Holocene emergence. In contrast the volcanic coastline (Catania to Capo Schiso) and the northeastern shoreline (Taormina to Milazzo) display widespread evidence of coastal emergence. Radiocarbon dated remains indicate that both the volcano and northeastern Sicily have been uplifted at a rate exceeding 1.5 mm a−1 during Holocene times, although more recent rates of uplift may have been greater. The pattern of uplift suggests that the northeastern coastline of Sicily, including the volcanic edifice, is apparently uplifting as a coherent unit, with superficial flank movements being superimposed on a regionally uplifting sub-volcanic basement.

Ground deformation monitoring of a potential landslide at La Palma, Canary Islands

Abstract The southern part of the island of La Palma comprises a north–south-oriented volcano known as the Cumbre Vieja. The steep gradient and high aspect ratio of the volcano, coupled with the prospect of future episodes of magma intrusion, highlight the potential for large-scale lateral collapse of the volcano, as recorded earlier in the history of La Palma and elsewhere in the Canary Islands. Historic eruptions of the Cumbre Vieja have occurred high up on the western flank of the volcano and along a single rift zone along the crest of the volcano. The geometry of the recent activity and faulting which occurred during an eruption in 1949 indicates that a discontinuity may be present beneath the western flank of the volcano, along which a future collapse may occur. To identify any displacement of the western flank overlying the discontinuity, a ground deformation network has recently been established on the volcano. The initial network spanned the fault system that developed on the upper flanks of the Cumbre Vieja during the 1949 eruption. This small network was measured in 1994, 1996 and 1997 using infrared Electronic Distance Measurement. In 1997, the network was enlarged and re-occupied, using the Global Positioning System, to incorporate the west flank and the southern part of the island. Although the results show that apparent displacements recorded during this period are within the error-margins of the techniques employed, the apparent movement vectors do suggest a coherent westward displacement of stations to the west of the 1949 fault system. Additional occupations of the network over the next few years will, however, be required to determine the reality or otherwise of this apparent coherent movement, and thus to decide whether or not the western flank of the Cumbre Vieja is currently sliding seaward. If not, it can be inferred that the volcano is stable during inter-eruptive periods.

Standardisation of the USGS Volcano Alert Level System (VALS): analysis and ramifications

The standardisation of volcano early warning systems (VEWS) and volcano alert level systems (VALS) is becoming increasingly common at both the national and international level, most notably following UN endorsement of the development of globally comprehensive early warning systems. Yet, the impact on its effectiveness, of standardising an early warning system (EWS), in particular for volcanic hazards, remains largely unknown and little studied. This paper examines this and related issues through evaluation of the emergence and implementation, in 2006, of a standardised United States Geological Survey (USGS) VALS. Under this upper-management directive, all locally developed alert level systems or practices at individual volcano observatories were replaced with a common standard. Research conducted at five USGS-managed volcano observatories in Alaska, Cascades, Hawaii, Long Valley and Yellowstone explores the benefits and limitations this standardisation has brought to each observatory. The study concludes (1) that the process of standardisation was predominantly triggered and shaped by social, political, and economic factors, rather than in response to scientific needs specific to each volcanic region; and (2) that standardisation is difficult to implement for three main reasons: first, the diversity and uncertain nature of volcanic hazards at different temporal and spatial scales require specific VEWS to be developed to address this and to accommodate associated stakeholder needs. Second, the plural social contexts within which each VALS is embedded present challenges in relation to its applicability and responsiveness to local knowledge and context. Third, the contingencies of local institutional dynamics may hamper the ability of a standardised VALS to effectively communicate a warning. Notwithstanding these caveats, the concept of VALS standardisation clearly has continuing support. As a consequence, rather than advocating further commonality of a standardised VALS, we recommend adoption of a less prescriptive VALS that is scalable and sufficiently flexible for use by local stakeholders via standardised communication products designed to accommodate local contingency, while also adhering to national policy.

Lateral collapse and tsunamigenic potential of marine volcanoes

Abstract The predominantly constructive life cycles of large, long-lived, stratovolcanoes and basaltic shields are punctuated by transitory episodes during which large volumes of material are divested from the flanks. Such shedding typically takes place catastrophically in the form of a lateral collapse, generating a debris avalanche and leaving a scar that may attain caldera dimensions. Collapse may follow instability development arising from a single, discrete, event, such as a crypto-dome intrusion, or may be the end-product of progressive destabilization over a long period of time. Lateral collapses may also occur at persistent slumps, which may have been active over periods as long as 104–105 a prior to catastrophic failure. Collapse velocities may exceed 40 m s−1, leading to completion of the process within a few hundreds of seconds. Collapse volumes span several orders of magnitude, ranging from less than 1 km3 to more than 10 km3 at many continental and subduction-zone volcanoes, to 1000 km3 or more at the great basalt shields of Hawaii. Lateral collapse may be accompanied by a wide range of associated hazards, including atmospheric shock wave, pyroclastic flows and surges, extensive tephra fall, and secondary lahars. For volcanoes in the marine environment, potentially destructive and lethal tsunamis can be added to the inventory. Here, the potential for a lateral collapse at an ocean island volcano to generate a ‘mega-tsunami’ (more than 100 m high at source and destructive at oceanic distances) is discussed and evaluated.

Global risk from extreme geophysical events: threat identification and assessment

In an increasingly interconnected world, any single geophysical hazard is capable of having consequences far beyond the range of immediate physical effects. Most recently, this was demonstrated by the 2004 Asian tsunami, which took the lives of citizens from 57 different nations, and by Hurricane Katrina in August 2005, which raised fuel prices worldwide and contributed to a record UK trade deficit in the month following the devastation of New Orleans. On an altogether wider scale, global geophysical events (GGEs) are natural phenomena capable of having wholesale deleterious consequences for the worlds environment, economy and society. These may arise (i) due to a global physical effect, such as an episode of severe planetary cooling in response to a volcanic ‘super-eruption’ or large comet or asteroid impact, or (ii) as a result of subsidiary ramifications for the global economy and social fabric of a cataclysmic regional event, such as an Atlantic- or Pacific-wide ‘mega-tsunami’, or a more spatially confined event at a strategically sensitive location, for example the awaited major Tokyo earthquake. While very infrequent, the wide-ranging—and potentially ruinous—consequences of a GGE for the well-being of the international community make it essential that they are seriously considered within any comprehensive assessment of natural threats.

The Archaeology of Geological Catastrophes

Archaeology is playing an increasingly important role in unravelling the details of geological catastrophes that occurred in the past few millennia. This collection of papers addresses both established and innovative archaeological methods and techniques, and their application in examining the impact of earthquakes and volcanic eruptions. This comprehensive volume includes case studies from around the world, such as Europe, Africa, SE Asia, Central and North America; covering historical and archaeological aspects of earthquakes and volcanic eruptions. Although the bulk of the collection views earthquakes and volcanic eruptions as agents of destruction, the volume also considers their potential benefits to past cultures - providing materials for tools, building and sculpture, and even the fertile environmental conditions on which societies depended. New geophysical, geological, and archaeometrical methods and techniques are described and the application of these new ideas presented, providing improved knowledge of these ancient catastrophes. There is a strong focus on arguably the most prominent geological catastrophe in the archaeological record - the Bronze Age eruption of Thera (Santorini, Greece) and its consequent regional impacts on Minoan culture. This multidisciplinary text is of benefit to academic researchers and educators in archaeology, palaeoseismology and volcanology alike.