Graduate Defense: Jerry Mock

Thesis Information

Title: Uav-Based Quantification Of Dynamic Lahar Channel Morphology At Volcan De Fuego, Guatemala

Program: Master of Science in Geophysics

Advisor: Dr. Jeffrey Johnson, Geosciences

Committee Members: Dr. Ellyn Enderlin, Geosciences; and Dr. Megan Cattau, College of Innovation and Design

Abstract

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. Abundant pyroclastic material from ongoing eruptive activity is remobilized seasonally during heavy precipitation, which can impact infrastructure and populations living near Fuego. Our region of focus was in an agricultural zone 6 to 10 km from the summit, surveyed with an Unoccupied Aerial Vehicle (UAV) quadcopter at monthly intervals. The imagery was processed into overlapping 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 (quantified in 500 m sections) to track channel morphology changes over time. The largest measured volume changes were a 490 m3/day loss in the upper section (~ 6 km from summit) and a 440 m3/day gain in the lower sections (~10 km from summit). We discuss how the natural channel’s 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 paroxysm.