Effects on agriculture depend on many factors; for example, ash can increase runoff in areas that have intense rainfall, or increase erosion in non-tilled farmland if less cohesive than the local soil (Nammah et al.1986). North of Crater Lake, Oregon, thick deposits of coarse pumice do not...
Figure 1. USGS uses DRE to rank the scale of some volcanic eruptions For example, if the eruption ofMount St Helen’sin the United States in 1980 is measured by the volcanic eruption index, its eruption volume (calculated in tephra) is about 1km³ to 1.3km³, so it belongs to aV...