The understanding of silicic eruptive transitions is key to mitigating the potential hazards of future eruptions. The diversity of rhyolitic eruptive products formed during a single eruption phase in the Laguna del Maule volcanic complex (LdM) allows the study of the factors governing the eruptive transitions. In this thesis, the reconstruction of the eruption histories, the processes preluding the transitions to effusive phases, the magma permeabilities, and the magmatic storage and ascent conditions are studied for the two first (Laguna del Maule and Los Espejos) and the youngest (Las Nieblas) postglacial rhyolites of LdM. The rhyolite of Laguna del Maule is the most voluminous rhyolitic deposit formed during a high explosive eruption due to the interaction of silicic melts with deeper and hotter mafic-to-intermediate magmas. The younger rhyolites did not interact with mafic magmas and were formed during smaller eruptions. The rhyolite of Los Espejos (rle) began with a phreatomagmatic phase followed by a subplinian magmatic eruption which formed a fall deposit which has dense pumices and vesicular obsidian clasts before the transition to an effusive stage. The permeability of the rle pumices is high (>10 -12 m 2 ) due to their high anisotropy and the localization of the degassing in some wide and elongate bubbles. The permeability localization allowed effective outgassing despite the increasing bubble collapse and densification of magma
during ascent. The effective outgassing together with a high total strain and a decrease of the magma ascent rate during the late stage of the subplinian eruption promoted the transition to the effusive phase. Unlike rle, the explosive-effusive transition of Las Nieblas (rln) eruption was promoted by a rapid decrease of the magma ascent rate based on the glassy groundmass of the obsidian lavas.
|Date of Award||24 Mar 2020|
- The University of Bristol
|Supervisor||Alison C Rust (Supervisor) & Katharine V Cashman (Supervisor)|