Volcanic Conduit Processes and Strombolian Eruption Cycles

University Of Hawaii, Honolulu

Investigators

Abstract

Volcanic Conduit Processes and Strombolian Eruption Cycles EAR-0207734 PIs: Harris & Houghton Our aim in this project is to understand the driving forces behind volcanoes that display persistent, strombolian activity. Such activity is characterized by repeated, mildly explosive events. For such repetitive explosive activity to be maintained over hundreds-to-thousands of years, as it has been at Stromboli Volcano (Italy), a volcano must be fed by a stable supply of magma and gas. It has not yet been determined, however, whether this supply occurs by the repeated rise of discrete magma batches or by a continuous stream. Initial measurements by us at Stromboli during May 1999 indicated that the magma supply to the shallow system may indeed be variable over minutes-to-hour long periods (i.e. it may be batch-like). These supply variations may in turn drive observed variations in the style and frequency of explosive activity. This has led us to develop a working hypothesis that fresh, gas-rich magma batches do rise from depth as discrete pulses, causing fluctuating levels of degassing and hence explosive activity upon their arrival. Our current project builds on those initial measurements by adding new geophysical instrumentation together with more detailed examination of volcanic products. In particular, we will use thermal and infrasound measurements, plus studies of the textures of the erupted lava bombs to examine explosive activity at Stromboli and infer variations in magma level within the conduit. Thermal data acquired during the persistent degassing that occurs between strombolian explosions will be used to characterize periods of enhanced gas escape. Finally, we will use vesicle (gas bubble) and crystal size distributions in the bombs to constrain the extent of mixing between newly arrived magma batches and long-resident magma within the shallow system.