Date of Award
Spring 2026
Abstract
Large-volume evolved magma eruptions are relatively uncommon in basalt-dominated rift environments, yet Iceland’s Northern Volcanic Zone (NVZ) repeatedly produces such eruptions within a plume-rift tectonic setting. The Askja Volcanic System (AVS) is one of the most prominent volcanic centers in the NVZ and has produced two major eruptions at ~10.9 ka and in 1875 CE. These eruptions mark important stages in the evolution of the Askja caldera system and provide an opportunity to investigate how magma assembly and transport evolve through time within an active rift-related volcanic plumbing system. Previous work on Icelandic volcanism has emphasized links between eruption frequency and deglaciation (Jull & McKenzie, 1996; Maclennan et al., 2002; Sims et al., 2013). However, the timescales of magma assembly and mobilization within the AVS plumbing system remain poorly constrained, and it remains unclear whether caldera formation reorganizes magma assembly conditions or whether magma transport processes remain consistent through time, particularly for historic eruptive units such as the 1875 eruption.Here I apply olivine Fe–Mg diffusion chronometry to basaltic eruptive products from the AVS that span both pre-caldera and post-caldera eruptive stages. Olivine crystals exhibit compositional zoning from Fo₇₀–Fo₈₃ cores to Fo₄₅–Fo₆₀ rims, recording late-stage chemical modification prior to eruption. One-dimensional diffusion models are applied to concentration profiles using experimentally determined Fe–Mg diffusion parameters (Dohmen & Chakraborty, 2007) and established diffusion chronometry frameworks (Costa et al., 2020). To improve spatial resolution of compositional profiles and address limitations associated with conventional spot-size analyses (>0.6 µm), I develop a complementary approach that integrates SEM–EDS imagery with grayscale intensity extraction in ImageJ, enabling higher-resolution transects and more precise characterization of diffusion gradients. Modeled diffusion timescales indicate short pre-eruptive residence intervals on the order of months to a few years, reflecting magma mingling and late-stage assembly rather than long-term storage. Similar diffusion times recorded in both pre- and post-caldera eruptive products indicate that magma ascent and shallow storage conditions beneath the AVS remain relatively stable despite caldera collapse and associated (presumed) reorganization of the volcanic plumbing system. These results contribute to the growing consensus that basaltic magmas have relatively short-lived residence in the Icelandic lithosphere.
Document Type
Master's Thesis
First Advisor
Julie G Bryce
Second Advisor
Florencia Fahnestock
Third Advisor
Emma Burkett
Department or Program
Earth Sciences
Degree Name
Master of Science
Recommended Citation
Rivera, Serafina rose, "Magma Dynamics Beneath the Askja Volcanic System Across the 1875 Eruption" (2026). Master's Theses and Capstones. 2085.
https://scholars.unh.edu/thesis/2085