The Cascadian region of the Pacific Northwest is perhaps best known for its stratovolcanoes, rising thousands of feet above the surrounding landscape. Debris flows initiating in the upper reaches of glacierized valleys are typically associated with intense, multi-day rain events, such as “Pineapple Express” storms. Although far smaller than large and deadly volcanic lahars, these rain-induced debris flows are nearly annual events and cause millions of dollars in damage. This investigation focuses on rain-induced periglacial debris flows on Mt. Hood and Mt. Rainier. There are several distinctive aspects about debris flows in this region: the steep slopes of the volcanoes provide high gradients, the initiation sites are typically near the glacier termini, and the receding glaciers have exposed even greater amounts of unconsolidated material in the steep moraines that are no longer buttressed by ice.
This research examined the triggering mechanisms of these debris flows from two perspectives: climatic and geomorphic. We will address the question “How does changing climate affect the frequency and magnitude of rain-induced debris flows from stratovolcanoes in the Cascades of the Pacific Northwest and, by extension, stratovolcanoes worldwide?” Our focus areas are Mt. Hood, Oregon and Mt. Rainier,
Washington. The objectives of the proposed research are to:
1. Identify and characterize the types of storms associated with rain-induced debris flows.
2. Determine if the frequency and character of these storms has changed over the past six decades.
3. Determine if antecedent snow cover conditions play an important role in the occurrence of debris flows and if snow cover conditions have changed over the past 25 years.
4. Develop and evaluate the use of rainfall thresholds for debris flows.
5. Evaluate the contribution of recent glacier recession to the increased susceptibility of debris flows.
