Pyroclasts: A Window into the Volcanic Conduit

Billions of people live in the shadow of a volcano. Explosive eruptions produce myriad hazards, saturating airways with noxious gases and volcanic particles that damage infrastructure and crops. Above all, these eruptions result in loss of life. Better mitigating these hazards necessitates study of their erupted products, which can help constrain the size, duration, and potential impact of future eruptions and give a glimpse into the subterranean volcanic conduit. In Chapter II, I study thousands of porous pyroclasts from the 1060 CE eruption of Medicine Lake Volcano. I find that pyroclast’s size, shape, and texture directly reflects conduit processes; sub-millimeter scale pyroclasts are more elongate and preserve elongated bubbles, whereas centimeter-scale pyroclasts are more blocky with roundish bubbles. In Chapter III, I use physical data from juvenile products to understand the explosive-effusive transition at 640 B.C. rhyolitic eruption of Newberry Volcano. I find pulsatory explosive behavior and changes in obsidian texture and proportion to herald the final switch to lava extrusion. In Chapter IV, I contextualize pumices from these eruptions with two eruptions from Mt. Mazama-Giiwas, finding that pumice in general can form from cyclic events of magma fragmentation and sintering. These studies not only change our modern perception of pyroclast formation and conduit dynamics, but also importantly provide data usable in numerical tephra dispersion models