GEOCHEMICAL MONITORING OF STAGNANT ICE FOR GLACIER OUTBURST FLOOD HAZARD ASSESSMENT, MOUNT RAINIER NATIONAL PARK

Outburst flooding (or jökulhlaup) occurs when a large volume of impounded water inside a glacier is rapidly released. Although outburst flooding occurs at low frequency, the impacts can be catastrophic. In 1955, an outburst flood from the Nisqually glacier destroyed Longmire, the operational headquarters of Mount Rainier National Park. There is an empirical association between stagnant (non-moving) glacier ice and destructive outburst floods. Determining the status and level of glacial stagnation is vital for protecting communities and infrastructure located in areas at risk of being impacted by glacial outburst floods.

It is hypothesized that the level of glacial stagnation can be determined from geochemical monitoring of glacial meltwater. A variety of geochemical signals (turbidity, dissolved iron, pH, conductivity, oxidation-reduction potential, total dissolved solids, temperature, and metal ion concentrations) were monitored for meltwater from the Nisqually glacier during the summers of 2012, 2014, 2016, and 2017. These water chemistry parameters were also measured for local streams fed by snowmelt for comparison. Glacial meltwater versus locally derived snowmelt showed a high degree of chemical differentiation. Significant changes in the pH of Nisqually glacier melt water have been observed over the time period, starting at a low point of pH = 6.05±0.11 in 2012, rising to a pH of 6.59±0.26 in 2016. During 2012, a relatively high concentration of dissolved iron (603 ppb on average) was also measured in the meltwater. Dissolved iron has subsequently been decreasing since 2012, reaching levels that are undetectable by field tests in 2017.

During the five years of monitoring, changes in the morphology of the Nisqually glacier have taken place. However, no outburst flooding has occurred during the period. A goal of this project is to correlate the changes in geochemistry to the behavior of the Nisqually glacier. Correlations between water chemistry, meltwater flow, and glacier velocity, as measured via satellite and aerial imagery, will be analyzed for evidence of Nisqually stagnation. Comparisons of geochemical signals for other glaciers at Mount Rainier will be used to investigate the transferability of these techniques.