Research Training Program

A large amount of past research has been done to analyze the effects of volcanic eruptions on climate and weather, yet the issue of seasonal change on volcanic eruptions has been relatively ignored. Rainfall may have the potential to increase and amplify the eruptive nature of a volcano. By penetrating and interacting with the magma chamber, the rainwater may be causing a significant increase in pyroclastic eruptions. To test this theory, the Costa Rican volcano, Arenal, was chosen as a case subject. Costa Rica has a unique rainy season, defined for purposes of this study as occurring between the dates of May 1^st and November 1^st. If indeed rainfall is affecting the nature of Arenal's eruptions, an increase in the seismic amplitude of the eruptions would result. Thus, a seasonal cycle should emerge, wherein such an increase would correspond with the rainy season of Costa Rica. In addition, ash collected around the volcano could reasonably be expected to demonstrate angularity compatible with an explosive eruption.

In this study, seismic records taken at Arenal were closely examined to determine if indeed there was a significant increase in seismic amplitude during the rainy season. Charts plotting average seismic values using daily, weekly, biweekly, and monthly averages for each separate year were examined within the context of the rainy season to approximate the overall pattern. No cycles or patterns were found within the data. The conclusion of this segment of the study was that there was no evidence for seasonal variation of eruptive activity within the seismic record. Ash collected from the close proximity to Arenal between the dates of 1987 to 1994 was examined using a Scanning Electron Microscope (SEM). The objective of this examination was to locate ash samples that showed angularity, thus indicating the ash was ejected from a solid-state magma that had been cooled by water. However, the findings revealed a greater number of ash samples that gave evidence of ejection from a fluid magma. Thus, the data gained in studying the ash again revealed no evidence for seasonal change in eruptive mode.