A Landscape Scale Analysis of Vegetation Change within the Blast Zone of the 1980 Mount St. Helens Volcanic Eruption through 2024

Abstract

The Mount St. Helens eruption of 1980 resulted in a catastrophic loss of vegetated land within the Pacific Northwest. This study focused on the vegetation throughout the blast zone with a particular interest in comparing vegetation growth patterns on different management areas and exploring environmental drivers of this growth. Using the Normalized Difference Vegetation Index (NDVI) for the years 1984 – 2024 in Emerging Hot Spot Analysis (EHSA), the results showed that vegetation growth was initially greater on properties where there were more remediation efforts following the eruption. In the later years of analysis, the EHSA identified locations on WEYCO where timber harvest was increasing. Therefore, WEYCO is experiencing a more inconsistent rate of growth while NVM continues to have an increase of vegetation growth each year. Multiple Linear Regression analysis (MLR) identified relationships between environmental variables such as slope, hillshade, elevation, and ash depth and vegetation attributes consisting of NDVI and canopy height. This analysis led to the conclusion that areas with greater canopy height and higher NDVI values could be found on steeper slopes with more sunlight exposure and lower initial volcanic ash deposits. These results point towards the potential for greater growth where management is more involved in reforestation efforts in this study area or other similar study areas. Additionally, care should be taken to focus efforts on gentle slopes, higher elevations, or areas where ash is present.