Modeling pyroclast transport and sedimentation in the Andean central and southern volcanic zones

Abstract

This thesis examines patterns of pyroclastic dispersal and sedimentation from active volcanoes located in the Andean Central and Southern volcanic zones. Numerical approaches are utilized, including single-particle trajectories, advection-diffusion and particle-tracking models, in order to gain insights into the impact of future volcanic eruptions in the region. Numerical models and wind data have been tested considering recent eruptions that have occurred in the Andes, and both tephra dispersal and recorded fallout have been successfully rebuilt. As volcanic zones are separated by several degrees of latitude, different environmental conditions are observed. For the Central Volcanic Zone interseasonal variability is present, and even opposite transport directions are observed between austral summer and winter months. Interannual variability is also detected, being mostly related to the El Nifio Southern Oscillation in the troposphere, and to the Quasi-Biennal Oscillation in the stratosphere. Outcomes from the modeling indicate that distal regions from the volcanic sources are likely to be impacted for tephra fallout, in particular when westward transport occurs during the summer (northern segment) or when eastward transport is intensified during winter (southern segment) . In contrast is the southernmost Southern Volcanic Zone where eastward transport is dominant throughout the year. Pyroclast dispersal is more widespread during the autumn-winter period, in connection with the arrival of frontal systems. Differences in atmospheric circulation between the upper troposphere and lower stratosphere are less evident at these latitudes. Probabilistic maps of tephra accumulation on the surface, derived for different eruptive scenarios, have been outlined for areas close to active volcanoes. Additionally, exceedance probability curves were estimated for places of interest. Volcanoes analyzed include El Misti in southern Peru, Parinacota in the Chile-Bolivia border and Lascar in northern Chile, which are located in the Central Volcanic Zone. Hudson volcano was selected from the Southern Volcanic Zone. Volcanic hazard implications are discussed for all case studies. In addition, pyroclastic transport and dispersal have also been addressed in some cases. Lahar flows were numerically simulated for Hudson volcano, and an estimation of the probability of occurrence of a moderate to high magnitude eruption was calculated. Some topics of the methodology are briefly discussed, including the importance of shape factor of particles on settling velocity. A sensitivity analysis of the estimated probability of tephra accumlation on the surface to the total number of simulations was investigated.EThOS - Electronic Theses Online ServiceGBUnited Kingdo