Publication Date

12-2016

Date of Final Oral Examination (Defense)

10-12-2016

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geophysics

Department

Geosciences

Supervisory Committee Chair

Jeffrey B. Johnson, Ph.D.

Supervisory Committee Member

Omar Marcillo, Ph.D.

Supervisory Committee Member

Brittany D. Brand, Ph.D.

Supervisory Committee Member

John Bradford, Ph.D.

Abstract

Infrasound waves generated during volcanic eruptions and recorded near the vent are used to study both changing atmospheric conditions and volcano eruption source characteristics. Infrasound data were recorded for a 32 month period at Volcán Tungurahua (Ecuador) by a five-station network located within 6.5 km from the vent. Infrasound detections made through cross-network correlation indicate cyclic eruptive behavior, which is corroborated by reports from the Ecuadorian monitoring agency. Cross-network correlation lag times are used to compute _10 m resolution infrasound source positions, which take into account NOAA models of local wind and temperature. Variable infrasound-derived source locations suggests source migration during the 32 months of analyzed data. Such source position variability is expected following energetic eruptions that destructively altered crater/vent morphology. Significant changes in crater/vent morphology are corroborated in imagery obtained during regular overflights.

Variations in cross-network lag times over short time periods (minutes to days) are observed when vent location is stable, and these variations are attributed to short term changes in atmospheric structure. Assuming a fixed source location, calculated air temperatures and winds in Tungurahua's vicinity (< 6:5 km) show evidence for both diurnal and semidiurnal tropospheric tides. Computed winds for the August 2012 eruptive period are predominantly easterlies and in agreement with both NOAA models and mapped ash deposits. Good agreement between computed wind directions and tephra deposits suggest that infrasound-derived winds can be utilized as input for ash dispersal modeling and can help to improve SO2 gas flux estimation.

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