Search

Volcanoes are not random phenomena, but owe their existence, location, morphology, and eruptive styles to tectonic plate motions. Volcanic landforms vary widely in size and morphology from the stereotypical towering glacier-clad stratovolcano. They range from small spatter cones to massive shield volcanoes several thousand cubic kilometers in volume or broad volcanic depressions, cinder cones being the most common volcanic construct. Their eruptions likewise span many orders of magnitude in volume. Evaluation of eruption magnitudes and frequencies contrasts the vast majority of mild-to-moderate eruptions (∼80% with volcanic explosivity index, or VEI ≤2) with the more infrequent larger, higher-impact events (5% with VEI ≥4). Increased risk from population growth in proximity to volcanoes has been mitigated by enhanced monitoring and hazard-reduction efforts.

To facilitate the assessment of hazards and risk from volcanoes, we have created a comprehensive global database of Quaternary Large Magnitude Explosive Volcanic Eruptions (LaMEVE). This forms part of the larger Volcanic Global Risk Identification and Analysis Project (VOGRIPA), and also forms part of the Global Volcano Model (GVM) initiative (http://www.globalvolcanomodel.org). A flexible search tool allows users to select data on a global, regional or local scale; the selected data can be downloaded into a spreadsheet. The database is publically available online at http://www.bgs.ac.uk/vogripa and currently contains information on nearly 3,000 volcanoes and over 1,800 Quaternary eruption records. Not all volcanoes currently have eruptions associated with them but have been included to allow for easy expansion of the database as more data are found. Data fields include: magnitude, Volcanic Explosivity Index (VEI), deposit volumes, eruption dates, and rock type. The scientific community is invited to contribute new data and also alert the database manager to potentially incorrect data. Whilst the database currently focuses only on large magnitude eruptions, it will be expanded to include data specifically relating to the principal volcanic hazards (e.g. pyroclastic flows, tephra fall, lahars, debris avalanches, ballistics), as well as vulnerability (e.g. population figures, building type) to facilitate risk assessments of future eruptions.

During late 2002 and early 2003, scientists at Llaima (central Chile) documented increases in seismicity, fumarolic output, a minor eruption, and pronounced glacial disruption. By 8 January 2003, the ice and snow formerly capping the N and S craters had completely melted. During January 2002–April 2003 eruptions remained comparatively modest. Larger eruptions began in April 2003, depositing pyroclastic material, dispersing numerous ballistic blocks, and creating substantial plumes. Llaima’s cover of ice and snow was more complete in October 2002 than in October 1998, so, by comparison, visible signs of thermal activity had diminished significantly. In contrast, seismicity in September 2002 was notably greater than in January 2002. Seismicity continued to increase from December 2002 to mid January 2003 before stabilizing for about 2 months. A flight on 8 January 2003 revealed dense fumarolic emissions from the main crater, no remaining ice or snow on the main crater’s internal walls, exposed rock at both the summit and Pichillaima (the smaller SE-flank cone), and numerous new crevasses in the cone’s glaciers. Although the melting came at the time of the annual thaw, the absence of ice and snow cover on both the shaded and unshaded sides of Llaima was cited as evidence indicating elevated rock temperatures. On the afternoon of 10 April, several ash explosions originated from the main crater. Strong and continuous explosions about 8–9 hours later caused ashfall in the Nslope sector of Captr n. The explosions became more sporadic, and continued into the morning of 11 April, when a column of volcanic gases fed a horizontal lenticular cloud ~ 30 km in diameter, the top of which rose to about 3,900 m altitude. This activity resulted in a thin layer of pyroclastic material spread widely across the flank glaciers, visible from the air out to distances of ~ 4 km. Impact craters in the ice testified to numerous bouncing and rolling projectiles. The crater floor contained a 50-m-diameter vent emitting gases. When photographed on 11 April, the ice and snow at Pichillaima had receded by 1–1.5 km from its topographic high. Many regions of the ice appeared to be in motion and undergoing acute mechanical failure, and numerous crevasses had developed. On 12–13 April, the main crater showed intense pulsing fumarolic degassing, mass wasting, and ballistic discharges. Eruptions began to contain significant tephra. On 16 April, gaseous emissions escaping from the crater reached 200 m above the crater rim. Emissions also came from Pichillaima. During 17 April, scientists witnessed gas emissions to the NE that ascended to 200 m above the crater rim and spawned a plume visible for ~10 km.