Professor Marcus Bursik Department of Geology University at Buffalo Buffalo, NY 14260 Abstract Many types of geophysical flows such as debris flows and pyroclastic flows can be classified as granular avalanches. While sedimentation from these volcanic granular flows leaves sometimes spectacular deposits that have been the subject of intense study for the past half-century, the effects of erosion have been more difficult to ascertain. Despite the relationship between slope angle and thickness of a stable layer of loose debris on a slope, which requires erosion during flow events, the positive change in volume of volcanic granular flows during transport has not been systematically studied. We present a model that simulates granular avalanches in which erosion as well as sedimentation cause significant changes in the mass and momentum during flow. We test the model against laboratory experiments and volcanological field data. We are able to obtain a reasonable fit of numerical model to both types of data.