URI volcanologists' analysis of 1883 Krakatau eruption helps assess volcanic hazards

December 17, 2001

Large-scale explosive eruptions from volcanoes located close to the sea often generate tsunamis that can carry volcanic fallout or flow material from such events onto distant coastal areas. URI Graduate School of Oceanography volcanologists Steven Carey, David Morelli, and Haraldur Sigurdsson and Butikno Bronto of the Volcanological Survey of Indonesia have studied the processes of tsunami deposition of past major eruptions to better understand how these volcanic deposits are important components of volcanic hazards assessment in coastal areas.

The team of scientists, funded by grants from the National Geographic Society Committee for Research and Exploration and the National Science Foundation, reported their analysis in a recent issue of Geology, the journal of the Geological Society of America.

They focused on the devastating tsunamis from the 1883 eruption of Krakatau volcano that claimed the lives of more than 35,000 people in Indonesia. Their quantitative analysis of volcanic particle shape illustrates the unique characteristics of tsunami deposits formed by some large-scale explosive eruptions.

Distinctive pumice deposits formed by the 1883 tsunamis from Krakatau have been recognized on the islands of Lagoendi, Sebuku, and Sebesi, located to the north of the Krakatau island group.

The scientific team used fractal analysis to discriminate the tsunami pumice deposits from those produced during other phases of the eruption. The Krakatau deposits suggest that tsunami deposits associated with major explosive eruptions are likely to be compositionally similar.

A key feature of explosive eruptions is the potential for generating large areas of floating pumice that may be rafted inland by tsunamis. This contrasts with non-volcanic tsunami deposits that are formed from locally derived sediment and provide no direct geologic link to the source event.

The ability to discern the source of volcanic deposits from tsunamis allows scientists to interpret coastal deposits in areas of active explosive volcanism and to unravel the evolution of deposition where volcanic products have come in contact with the sea.

The distinctive characteristics of volcanic deposits provide clues to the source of the material and how volcanic material is transported during tsunamis. Recognition of these types of deposits provides an important component to the analysis of volcanic hazards in coastal zones that occur in areas of active explosive volcanism.

"We now have an appreciation that these types of deposits indicate a catastrophic event associated with the coupling between the tremendous power of a volcanic eruption and the sea," said Carey.
The URI Graduate School of Oceanography is one of the country's largest marine science education programs, and one of the world's foremost marine research institutions. Founded in 1961 in Narragansett, RI, GSO serves a community of scientists who are researching the causes of and solutions to such problems as acid rain, global warming, air and water pollution, oil spills, overfishing, and coastal erosion.

GSO is home to the Coastal Institute, the Coastal Resources Center, Rhode Island Sea Grant, the Ocean Technology Center, and the National Sea Grant Library.

University of Rhode Island
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