Glacial changes between 1985--2009 and implications for volcanic hazards at Mt. Rainier, Washington

Scope and Method of Study: Thermal Infrared Landsat scenes (Band 6) were collected and analyzed to quantify area changes and rates of change of Mt. Rainier glaciers between 1985 and 2009. Glacier change data was compared to measurements made by the United States Geological Survey (USGS) and the Global Land Ice Measurements from Space (GLIMS) project. The modeled glacier area at Mt. Rainier for the last 10 ka was then compared to the eruptive history of Mt. Rainier and other Cascade volcanoes to examine correlations.;Findings and Conclusions: Landsat scenes show a steady decrease in glacier area at Mt. Rainier, consistent with USGS and GLIMS measurements. The observed area of Mt. Rainier glaciers decreased from 85.590 km² to 81.355 km² (5.32%) from 1985-2009. If glacier loss continues, the risk of hazards such as jokulhlaups (glacial outburst floods) and lahars could be enhanced due to the increased amount of glacial melt. Decreases in glacier ice at Mt. Rainier could also lead to an increased risk of eruptions due to decompression of the magma chamber. A continuation of the glacier loss seen in this study could be enough to trigger decompression, especially if Mt. Rainier has a shallow magma chamber. However, it is unclear what the time lag would be between glacier loss and an eruption as well as the amount and rate of glacier loss that would be needed. Previous studies indicate that there was an increase in eruptions ∼7.4-5 ka, which is ∼3.6-6 ka following the last glacial maximum. During the last ∼2.3 years, eruption rates of Cascade volcanoes have increased during times when the modeled glacier area decreased. This strongly suggests a correlation between eruption rates and glacier coverage. Glaciers at Mt. Rainier should therefore continue to be closely monitored in the future because of a possible increased risk of debris avalanches, lahars, jokulhlaups, and eruptions. Satellite-based remote sensing such as the Landsat images used in this study can be a valuable tool for monitoring Mt. Rainier glaciers. Future monitoring through remote sensing would allow glacier areas to be consistently tracked and provide data needed to assess hazard risks.