Lava dome studies: Insights into internal structures and growth processes
Bernstein, Marc Louis
MetadataShow full item record
This thesis presents the results of multiple investigations using thermal imaging, structural mapping, and data analysis for lava domes throughout Latin America and the Caribbean. The lava domes that were studied are: Soufrière Hills on the island of Montserrat (16.72°N, 62.18°W), Cerro Negro de Barriales in the Atacama region of Chile (23.48°S, 67.37°W), Colima in Mexico (19.51°N, 103.62°W), the Brujo, Monje and Mitad lava domes at the Santiaguito dome complex in Guatemala (14.76°N, 91.55°W), and the Chaitén Volcano also in Chile (42.83°S, 72.65°W). The intent of these studies was to improve our understanding of lava dome internal structures and growth processes to gain better insight about potential hazards and risks. Thermal imaging of the Colima lava dome revealed the existence of multiple simultaneously active flow paths within this slow-growing andesitic lava dome, as well as the role the talus plays in enhancing the vertical growth of the lava dome. Thermal imaging of the Chaitén lava dome also revealed the presence of multiple flow paths within this fast-growing rhyolitic lava dome, and highlighted the role of extrusion rate in controlling lobe morphology. Intrusion of a large spine within the lava dome may have had structural consequences including the possible triggering of a dome collapse. At Soufrière Hills, a novel method was developed for determining the daytime heating correction of thermal images by imaging a target of the same composition in a similar camera-target-sun relationship as the actual lava dome. The correction reaches 26 °C in the early afternoon. Video analysis of a Vulcanian explosion on 8 January 2010 indicates there may have been two explosion sources and that ejection velocities were at least 95 m s -1 . Thermal imagery shows evidence of several reinvigorating pulses in pyroclastic density currents, as well as the first documented evidence for a collision between two pyroclastic flows. Both of these imply more then one source and one flow subsequent to the 8 January 2010 explosion. Analysis of seismic signals does not show a correlation between rockfalls from the lava dome and time-of-day during eruptive pauses. Measurements of fumarole temperatures over a period of four months show that it is possible to monitor fumarole temperature trends using a thermal imaging camera. A comparison of rainfall data and SO2 gas output in late 2007 does not support the hypothesis that gas scrubbing is taking place during heavy rain. A simple model for Colima volcano provides a plausible explanation for the occurrence of fumaroles located on the crater walls. This is supported by thermal imaging at Soufrière Hills showing the existence of fumaroles confined by bedding layers within talus deposits. Fieldwork at Cerro Negro de Barriales, a partly eroded and inactive lava dome, revealed radial fractures in the lava dome that expose the core-to-carapace transition. These fractures may be the result of a late-stage dome intrusion expanding the pre-existing dome and carapace. Riedel shears at the base of the carapace indicate motion of the carapace relative to the underlying core when both were brittle. Localized penetration of core material into the carapace may indicate an incipient transition from endogenous to exogenous growth. At Santiaguito, mapping from air photos and in the field, along with petrological and chronological evidence, support the hypothesis that an underlying dike connects the lava domes.