volcanic explosivity index

volcanic explosivity index
Name	Volcanic explosivity index
Type	scale
First used	1982

Contents

Overview
Scale and Criteria
Historical and Notable Eruptions
Measurement Methods and Data Sources
Impacts and Hazards
Limitations and Criticism
See also

volcanic explosivity index

The volcanic explosivity index is a quantitative scale for comparing the relative explosiveness of explosive volcanic eruptions. Developed to standardize descriptions of eruption magnitude and plume height, the index is widely cited in assessments of volcanic risk, paleovolcanology, and hazard planning for regions near Mount St. Helens, Krakatoa, Mount Pinatubo, Eyjafjallajökull, and other eruptive centers. It links eruptive volume and dispersal with historical and geologic records used by institutions such as the United States Geological Survey, Smithsonian Institution, and regional volcano observatories.

Overview

The index provides a logarithmic classification system that orders eruptions by erupted tephra volume and plume height; it is comparable in intent to the Richter magnitude scale for seismic events and the Saffir–Simpson scale for tropical cyclones. Widely adopted in volcanic literature, the scale interfaces with datasets maintained by the Global Volcanism Program, national agencies like the Geological Survey of Canada, and research centers at universities including University of Cambridge and Massachusetts Institute of Technology. It is used to communicate eruption severity in reports from organizations such as the World Meteorological Organization and the Intergovernmental Panel on Climate Change when assessing climatic effects of large eruptions.

Scale and Criteria

The index ranges across discrete steps that represent increasing orders of magnitude in erupted tephra volume, eruption cloud height, and qualitative descriptions. Analogous to the Moment magnitude scale’s logarithmic progression, each integer increase corresponds to about a tenfold increase in erupted volume, with typical thresholds tied to cubic kilometers of tephra and observed plume heights recorded at Hawaiian Islands, Aleutian Islands, and Iceland. The scale’s categories are used in cataloguing by the National Oceanic and Atmospheric Administration and are incorporated into hazard maps produced by agencies such as the Italian National Institute of Geophysics and Volcanology.

Historical and Notable Eruptions

Notable eruptions assigned high index values include the 1815 event at Mount Tambora, the 1883 eruption of Krakatoa, the 1991 eruption of Mount Pinatubo, and prehistoric events linked to volcanic centers like La Garita Caldera and the Yellowstone Caldera. Historical accounts from contemporaries in the British East India Company era and instrumental records preserved in archives at institutions like the Royal Society inform estimates for 18th- and 19th-century eruptions, while tephrochronology and radiometric dating used by teams at University of California, Berkeley and University of Oxford refine magnitudes for older events.

Measurement Methods and Data Sources

Quantification relies on field measurements of tephra deposit thickness, isopach mapping, and grain-size analysis conducted by researchers at facilities such as Lamont–Doherty Earth Observatory and Scripps Institution of Oceanography. Satellite remote sensing from platforms operated by European Space Agency and National Aeronautics and Space Administration provides plume height and ash dispersion data used in near-real-time classification for eruptions like those at Mount Redoubt and Sakurajima. Paleovolcanology integrates stratigraphic correlation, radiocarbon dating from laboratories at Max Planck Institute for Chemistry, and geochemical fingerprinting undertaken at institutions like ETH Zurich to attribute deposits to specific eruptions catalogued by the Global Volcanism Program.

Impacts and Hazards

Higher index values correlate with wide-ranging impacts documented in studies by the World Health Organization and the Food and Agriculture Organization regarding ashfall effects on agriculture, infrastructure, and public health, as observed after eruptions at Mount Pinatubo and Mount St. Helens. Climatic consequences—such as short-term stratospheric aerosol loading and global temperature anomalies—have been assessed in analyses published by the Intergovernmental Panel on Climate Change and modeled by teams at Princeton University and University of Reading. Aviation hazards and subsequent responses by authorities like the International Civil Aviation Organization were prominent during events like the 2010 Eyjafjallajökull eruption.

Limitations and Criticism

Critics from research groups at University of Washington and policy analysts at RAND Corporation note that the index emphasizes erupted volume and plume height while providing limited information on eruption style, duration, effusive versus explosive behavior, and impacts on local populations. The scale’s coarse, logarithmic steps can obscure distinctions between eruptions with similar volumes but different dispersal and hazard profiles; this limitation is discussed in literature from the American Geophysical Union and at international conferences hosted by the International Association of Volcanology and Chemistry of the Earth's Interior. Alternative or complementary metrics, including eruption duration indices and intensity curves developed at centers like University of Tokyo and University of Lisbon, address some of these gaps.