Optical and Radar Satellite Measurement of Volcanic Eruption Impacts on Vegetation

Vegetation disturbance caused by volcanic eruptions can span large areas and persist for years, yet remains poorly constrained and underutilised as a tool for understanding eruptive processes. Many volcanoes are located in forested and remote regions, where access is limited and field observations are difficult. In this thesis, I explore how optical and radar satellite remote sensing can be used to detect, quantify, and analyse vegetation disturbance and recovery caused by volcanic eruptions and emissions at volcanoes worldwide, encompassing a range of eruptive styles and environmental settings, to assess the global applicability of these methods.

This thesis is structured around three core investigations. First, in Chapter 2, I analyse vegetation disturbance and regrowth following the 2015 eruption of Calbuco, Chile, using Sentinel-2 NDVI time series and Sentinel-1 radar backscatter and coherence. I use this case study to test different methods and assess the most effective earth observation tools for studying vegetation disturbance at volcanoes. I demonstrate how declines in vegetation health and coverage correlate with deposit type, thickness and distribution, and show that forest recovery times vary with impact type and possibly local topography. These results are used to refine isopach maps and estimate eruption volume based on vegetation damage.

In Chapter 3, I assess the effects of volcanic gas emissions, particularly SO2, on forest health, using multi-year optical and radar observations at Krakatau, Semeru, Reykjanes Peninsula, Turrialba and Masaya. I show that both short-term eruptive plumes and long-term passive degassing cause measurable impacts to vegetation from satellite data, with spatial patterns and recovery trajectories linked to gas flux, exposure time, and vegetation type.

Finally, in Chapter 4, I present a global comparison of forest disturbance and recovery across 18 volcanoes, quantifying recovery times by disturbance type and forest biome. Tephra-affected areas recover most rapidly, while PDC and blast zones show much longer recovery times on the order of decades. Tropical forests recover faster than temperate ones, suggesting ecological resilience plays a major role. In general, the majority of impacted areas recover in as little as 30 years but flow deposits can significantly alter the vegetated landscape for hundreds to thousands of years.

Across all chapters, I highlight the value of optical and radar satellite data to monitor ecological impacts of eruptions, particularly when combined or used in conjunction with field campaigns. These methods offer new ways to assess eruption magnitude, map deposit extents, and evaluate ecosystem recovery, particularly in inaccessible regions. The findings also point toward broader applicability to other disturbance types, and show how vegetation change can be a useful proxy for understanding volcanic activity.