Publication Date
12-2023
Date of Final Oral Examination (Defense)
10-27-2023
Type of Culminating Activity
Thesis
Degree Title
Master of Science in Geophysics
Department Filter
Geosciences
Department
Geosciences
Supervisory Committee Chair
Jeffrey B. Johnson, Ph.D.
Supervisory Committee Member
Ellyn Enderlin, Ph.D.
Supervisory Committee Member
Megan Cattau, Ph.D.
Abstract
Lahars are responsible for 26% of the deaths associated with volcanic activity reported since 1500 AD, and are extremely destructive to infrastructure (Thouret et al., 2020). Secondary lahars are volcanic mudflows commonly triggered by rainfall. Valuable land and buildings may be covered or destroyed by thick deposits including heavy boulders, mud, and debris. Bridges and roads can be washed out, cutting people off from vital services and potentially placing them in danger from other hazards. Volcán de Fuego in Guatemala actively produces pyroclastic material in small Strombolian eruptions every 15-20 minutes. Fuego occasionally has larger eruptions and has produced over 50 with a Volcanic Explosivity Index (VEI) ≥ 2 since 1524 (Naismith et al., 2019). In June of 2018, a set of pyroclastic currents filled more than 12 km of the Las Lajas drainage. The abundant pyroclastic material from ongoing eruptive activity is remobilized seasonally during heavy precipitation, which can impact infrastructure and populations living near Fuego. This study quantifies erosional and depositional processes for secondary lahars in Las Lajas drainage at Volcán de Fuego, Guatemala during the May through October 2021 rainy season. The region of focus was in an agricultural zone 6-10 km from the summit, surveyed with an Unoccupied Aerial System (UAS) quadcopter at monthly intervals. The imagery was processed into time-lapse structure from motion digital elevation models (DEMs). DEMs were differenced to find volumetric changes as a function of the channel flow path distance to track channel morphology changes over time. The methods explored in this study to difference DEMs from UAS data have been adapted in a collaborative effort between myself and Instituto Nacional de Sismología, Vulcanologia, Meteorología e Hidrología (INSIVUMEH) in Guatemala to develop a streamlined workflow for change detection and erosion monitoring along lahar channels. The largest measured volume changes were a 490 m3/day loss in the upper-most section (~ 6.0-6.5 km from summit) and a 440 m3/day gain in the lowest section (9.3-9.8 km from summit). The natural constriction and widening of Las Lajas in more distal sections control the behavior and stability of the stream evolution. Above the constriction, the channel is primarily downcutting and meandering within an old flood plain, which had been filled in by pyroclastic materials deposited by the June 2018 eruption. The Morphological Activity Factor (MAF) is a novel measurement I developed to quantify the amount of change happening where deposition and erosion are occurring next to each other in the transition from erosion to deposition along the channel.
DOI
https://doi.org/10.18122/td.2184.boisestate
Recommended Citation
Mock, Jerry Clay, "UAS-Based Quantification of Dynamic Lahar Channel Morphology at Volcán de Fuego, Guatemala" (2023). Boise State University Theses and Dissertations. 2184.
https://doi.org/10.18122/td.2184.boisestate
