Geochemical and Textural Constraints on Eruptive Behavior of Merapi Volcano, Indonesia

Furman

EAR- 0230208

Merapi Volcano in Central Java, Indonesia, is one of Earth's most active and dangerous volcanoes. This stratovolcano has been active for over 40,000 years, with nearly continuous eruptive activity over the past century. Merapi is particularly feared because of the potentially explosive nature of its activity, and because several hundred thousand people live in high-risk areas on the volcano flank. This project uses a combination of tephrostratigraphic, geochemical and CSD techniques to address the rheological (e.g., thermal state, magma composition, glass chemistry, crystal nucleation and growth rate) controls on the full spectrum of Merapi's eruptive behavior. The results of this project will provide fundamental information on magma reservoir and conduit conditions and processes, as well as insights on the potential for future larger-scale explosive activity.

The intellectual merit of the research derives from the application of detailed textural analysis of lavas and tephras to the identification of intensive parameters associated with eruptive activity. That is, one can relate crystal size distribution patterns of individual eruptive units to the detailed chemical, barometric and thermal history of Merapi volcano. Analysis of melt inclusions in olivine crystals also provides insight into late-stage magmatic processes, including helping to distinguish crystal growth related to decompression from that resulting from magma mixing or hybridization. When used in conjunction with our textural analyses, this technique provides a powerful method for evaluating magma ascent rates and residence times. This information is critical to the study of explosive volcanic systems because the eruptive intensity is linked directly to both the residence time of magma within the chamber and the degree of solidification that occurs within the reservoir and conduit. In volcanic systems that tend to be highly crystalline (e.g., Merapi lavas contain up to 50% crystals upon eruption), magma that is nearly solidified may fill the eruptive vent to substantial depths, effectively plugging the vent system and leading to infrequent but very dangerous eruptions. Using chemical and textural data, it becomes possible to gauge the conditions leading to violent eruptions. By recognizing precursor signals to major eruptions, the ability to anticipate catastrophic situations can be improved.

The broader implications of this project include both human resource development and potential assistance for volcanic hazard mitigation. This project will fund the doctoral research of one female graduate student at Penn State and the postdoctoral research of a female Indonesian volcanologist from the Volcanological Survey of Indonesia. The work will strengthen an extant relationship between Penn State and the Volcanological Survey of Indonesia that has focused on monitoring active volcanoes with the goal of improving disaster preparedness. In recent decades Merapi has had fairly small eruptive events with a frequency of two to five years. The geologic record, however, indicates that this recent activity encompasses only a small portion of the full range of explosivity that has occurred in the past. At least seven eruptions between 3000-250 years ago were larger and farther-reaching explosive events than any recorded in the 20th century. Unfortunately, current hazard assessment and contingency planning is based primarily upon small eruptive events, while the earlier record of major explosive eruptions suggests that effective planning needs to consider the full range of Merapi's eruptive behavior. It is anticipated that this study will enable researchers to identify precursor events to major eruptions that will prove useful in modern hazard mitigation efforts.