In November 2006 a Pineapple Express rainstorm moved through the Pacific Northwest generating record precipitation, 22 to 50 cm in the two-day event on Mt. Rainier. Copeland (2009) and Legg (2013) identified debris flows in seven drainages in 2006; Inter Fork, Kautz, Ohanapecosh, Pyramid, Tahoma, Van Trump, and West Fork of the White River. This study identified seven more drainages: Carbon, Fryingpan, Muddy Fork Cowlitz, North Puyallup, South Mowich, South Puyallup, and White Rivers. Twenty-nine characteristics, or attributes, associated with the drainages around the mountain were collected. Thirteen were used in a regression analysis in order to develop a susceptibility map for debris flows on Mt. Rainier: Percent vegetation, percent steep slopes, gradient, Melton's Ruggedness Number, height, area, percent bedrock, percent surficial, percent glacier, stream has direct connection with a glacier, average annual precipitation, event precipitation, and peak precipitation. All variables used in the regression were measured in the upper basin. Two models, both with 91% accuracy, were generated for the mountain. Model 1 determined gradient of the upper basin, upper basin area, and percent bedrock to be the most significant variables. This model predicted 10 drainages with high potential for failure: Carbon, Fryingpan, Kautz, Nisqually, North Mowich, South Mowich, South Puyallup, Tahoma, West Fork of the White, and White Rivers. Of the remaining drainages 5 are moderate, 10 are low, and 9 are very low. Model 2 found MRN (Melton's Ruggedness Number) and percent bedrock to be the most significant. This model predicted 10 drainages with high potential for failure during future similar events: Fryingpan, Kautz, Nisqually, North Mowich, Pyramid, South Mowich, South Puyallup, Tahoma, Van Trump, and White Rivers. Of the remaining drainages, 6 are moderate, 9 are low, and 9 are very low. The two models are very similar. Initiation site elevations range from 1442 m to 2448 m. Six of the thirteen initiation sites are above 2000 m. Proglacial gully erosion initiated debris flows seem to occur at all elevations. Those debris flows initiated partially by landslides occur between 1400 and about 1800 m. The combined regression analysis model for the Mt. Rainier, Mt. St. Helens, Mt. Hood, and Mt. Adams raised the predictive accuracy from 69% (Olson, 2012) to 77%. This model determined that percent glacier/ice and percent vegetation were the most significant.

Debris flow initiation is controlled by a complex interaction of geology, geomorphology, climate, and weather. In the Cascade Range of Pacific Northwest and mountainous areas globally, patterns of temperature and precipitation are being altered by climate change, which may in turn impact debris flow initiation. Temperature has increased and patterns of precipitation have changed, potentially impacting the timing, geography, and triggering mechanisms of debris flows. Glacier retreat since the end of the Little Ice Age has exposed volumes of unstable sediment on steep slopes prone to debris flow initiation. Earlier spring snowmelt extends the snow-free window when rainstorms may mobilize sediment, resulting in debris flows. To ascertain the presence of a climate change signal we examined the timing, geography, and initiation mechanisms of recent (2001 to 2006) non-volcanic debris flows from Mount Rainier, Washington, the highest volcano in the Cascade Range with the largest ice-volume in the conterminous United States. Debris flows damage infrastructure, requiring costly repairs. Debris flows also deposit volumes of sediment in streams, potentially exacerbating future flood hazards. To characterize recent debris flows, field reconnaissance was conducted summer 2008 along suspected debris flow paths from initiation to deposition. Results from summer fieldwork were used in conjunction with analysis of aerial photography, Light Detection and Ranging (LiDAR), and other data to determine characteristics of debris flow initiation sites, such as elevation, slope, orientation, upslope contributing area, and proximity to glaciers. Recent debris flow initiation sites were also examined in reference to glacier characteristics, such as elevation of glacier termini, glacier retreat, orientation, area, and volume, for the years 1913, 1971, and 1994 from past work by Nylen (2004). Characterization of debris flow initiation sites and definition of the locations of longitudinal transitions in debris flow behavior allows estimation of future debris flow hazards also allows inferences to be drawn regarding initiation mechanisms to be inferred and suggests a trajectory for changing debris flow hazards due to climate change. Debris flows at Mt. Rainier occur in late summer through fall and recent events were no exception, occurring from August through November. A total of twelve debris flows occurred in six stream channels during the period of 2001 to 2006. Three channels not previously known to have experienced debris flows, two south-facing and one north-facing, were impacted. Debris flows tracks led up to glacier meltwater fed, steep-walled channels or gullies in unvegetated, unconsolidated Quaternary-age material immediately downslope of glacier margins. Debris flows initiated at an average elevation of 2181 m and an average channel gradient of 39°. While glaciers appear to play a key role in debris flow initiation, simple glacier metrics could not be used to distinguish glaciers near debris flow heads from those without proximal debris flows heads. All but one of the twelve debris flows initiated during rainfall. The single debris flow that occurred during dry-weather is described by Vallance et al. (2002). Rainfall induced debris flows in 2003, 2005, and 2006 were not associated with landslide scarps, rockfalls, or other indications of large slope failures. Rather, debris flows initiated in steep-walled gullies fed by glacier meltwater that were visible on aerial photography prior to the first known debris flow initiation in a particular channel. The steep flanks of Mt. Rainier contain many similar gullies that have not previously been associated with debris flows, but debris flow producing gullies are at higher elevations than gullies not associated with debris flows. The small population of recent debris flows and incomplete historic record of debris flows for the periods 1926 to 1985 and 1993 to 2001 limits analysis of changes in debris flow timing, geography, or triggering mechanism. The magnitude of recent events may have initially appeared greater than historic events as the 2005 and 2006 storms are the only ones known to have produced multiple debris flows in the recorded history of Mt. Rainier National Park. Yet much of the damage initially attributed to debris flows was due to widespread, severe flooding. Ongoing, detailed record keeping and possibly reconstruction of past events through paired geomorphic reconnaissance and dendrochronology is needed before conclusions regarding the impacts of climate change on debris flow initiation can be reached.

Debris flows caused by heavy rains occurred in November of 2006 on several Cascade volcanoes. Mt. Adams experienced debris flows in seven of eighteen drainages including Adams Creek, Big Muddy Creek, Lewis Creek, Little Muddy Creek, Muddy Fork, Rusk Creek and Salt Creek. Six debris flows occurred on the northeast side of the mountain. A landslide initiated one debris flow, three were initiated by heavy water flow and in channel landslides, and three were initiated by a coalescence of eroded channels (headless debris flows). Four pre-2006 debris flows were found in the Cascade Creek, Crofton Creek, Hellroaring Creek and Morrison Creek drainages. Every 2006 debris flow initiated in Quaternary glacial drift. Attributes of the drainages were investigated to determine differences between drainages with debris flows and those without. The upper basins of drainages with debris flows averaged 37% glacial coverage, 29% bedrock and 35% unconsolidated material. The upper basins of drainages without debris flows without averaged 12% glacial coverage, 63% bedrock, and 25% unconsolidated material. All of the drainages with debris flows were directly connected to a glacier, opposed to only 36% of the drainages without debris flows. Drainages with debris flows averaged 18% slopes above 33°, 10% vegetation, a gradient of 0.38, a Melton's Ruggedness Number of 0.62, an average annual rainfall of 2.16 m, and -52% glacier lost between 1904-2006. The upper basins of drainages without debris flows averaged 11% slopes above 33°, 18% vegetation, a gradient of 0.31, a MRN of 0.58, an average annual rainfall of 2.38 m, and -41% glacier lost between 1904-2006. A multiple logistic regression was performed to determine factors with highest influence on predicting the probability of a debris flow. Influencing factors were percent glacial coverage and average annual rainfall. They predicted the 2006 debris flows with an 89% accuracy rate. This model was used to produce a debris flow hazard map. Due to the number of Cascade volcanoes that experienced debris flows as a result of the November 2006 storm, data of this type could be combined from multiple mountains to construct a general Cascade Mountain debris flow hazard model.

Debris flows, which occur in mountain settings worldwide, have been particularly damaging in the glaciated basins flanking the stratovolcanoes in the Cascade Range of the northwestern United States. This thesis contains two manuscripts that respectively investigate the (1) initiation processes of debris flows in these glaciated catchments, and (2) debris flow occurrence and its effect on valley bottoms over the last thousand years. In a 2006 storm, seven debris flows initiated from proglacial gullies of separate basins on the flanks of Mount Rainier. Gully heads at glacier termini and distributed collapse of gully walls imply that clear water was transformed to debris flow through progressive addition of sediment along gully lengths. In the first study, we analyze gully changes, reconstruct runoff conditions, and assess spatial distributions of debris flows to infer the processes and conditions necessary for debris flow initiation in glaciated catchments. Gully measurements suggest that sediment bulking requires steep gradients, abundant unstable material, and sufficient gully length. Reconstruction of runoff generated during the storm suggests that glaciers are important for generating the runoff necessary for debris flow initiation, particularly because infiltration capacities on glacial till covered surfaces well exceed measured rainfall rates. Runoff generation from glaciers and abundant loose debris at their termini explain why all debris flows in the storm initiated from proglacial areas. Proglacial areas that produced debris flows have steeper drainage networks with significantly higher elevations and lower drainage areas, suggesting that debris flows are associated with high elevation glaciers with relatively steep proglacial areas. This correlation reflects positive slope-elevation trends for the Mount Rainier volcano. An indirect effect of glacier change is thus the change in the distribution of ice-free slopes, which influence a basin's debris flow potential. These findings have implications for projections of debris flow activity in basins experiencing glacier change. The second study uses a variety of dating techniques to reconstruct a chronology of debris flows in the Kautz Creek valley on the southwest flank of Mount Rainier (Washington). Dendrochronologic dating of growth disturbances combined with lichenometric techniques constrained five debris flow ages from 1712 to 1915 AD. We also estimated ages of three debris flows ranging in age from ca. 970 to 1661. Run-out distances served as a proxy for debris flow magnitude, and indicate that at least 11, 2, and 1 debris flow(s) have traveled at least 1, 3, and 5 km from the valley head, respectively since ca. 1650. Valley form reflects the frequency-magnitude relationship indicated by the chronology. In the upper, relatively steep valley, discrete debris flow snouts and secondary channels are abundant, suggesting a process of debris flow conveyance, channel plugging, and channel avulsion. The lower valley is characterized by relatively smooth surfaces, an absence of bouldery debris flow snouts, few secondary channels, and relatively old surface ages inferred from the presence of tephra layers. We infer that the lower valley is deposited on by relatively infrequent, large magnitude, low-yield strength debris flows like an event in 1947, which deposited wide, tabular lobes of debris outside of the main channel. Debris flows during the Little Ice Age (LIA) predominantly traveled no further than the upper valley. Stratigraphic evidence suggests that the main Kautz Creek channel was filled during the LIA, enhancing debris flow deposition on the valley surface and perhaps reducing run-out lengths. Diminished areas and gradients in front of glaciers during the LIA also likely contributed to decreased run-out lengths. These findings suggest that changes in debris flow source and depositional zones resulting from temperature and glacier cycles influence the magnitude and run-out distances of debris flows, and the dynamics of deposition in valley bottoms.

Powerful Pacific storms strike the region. Otherworldly lenticular clouds often cap Mount Rainier. Rain shadows create sunny skies while torrential rain falls a few miles away. The Pineapple Express brings tropical moisture and warmth during Northwest winters. The Pacific Northwest produces some of the most distinctive and variable weather in North America, which is described with colorful and evocative language in this book. Atmospheric scientist and blogger Cliff Mass, known for his ability to make complex science readily accessible to all, shares eyewitness accounts, historical episodes, and the latest meteorological knowledge. This updated, extensively illustrated, and expanded new edition features: • A new chapter on the history of wildfires and their impact on air quality • Analysis of recent floods and storms, including the Oso landslide of 2014, the 2016 “Ides of October” windstorm, and the tornado that damaged 250 homes in Port Orchard on the Kitsap Peninsula in 2018 • Fresh insight on local weather phenomena such as “The Blob” • Updates on the latest technological advances used in forecasting • A new chapter on the meteorology of British Columbia Highly readable and packed with useful scientific information, this indispensable guide is a go-to resource for outdoor enthusiasts, boaters, gardeners, and anyone who wants to understand and appreciate the complex and fascinating meteorology of the region.

Many countries are increasingly threatened by major landslide disasters and fatalities due to extreme weather events which have major implications for public safety and the sustainability of infrastructure and the built environment. A further increase in such a trend could come from climate change. This book helps to fill in the gap due to the fact that landslide hazards are commonly not covered under the policy debate on climate change. The book highlights the importance of raising awareness to the challenges of landslide hazards due to climate impact. It provides a holistic frame for understanding the key issues and new tools that could be used to assess and manage the landslide risks. The book gathers contributions from 21 countries and regions in the form of national reports or summaries with respect to four key aspects: a) the methods used for evaluating changing weather and changing landslide patterns; b) the changing weather patterns; c) the changing landslide patterns and hazard scenarios; d) the applications to risk management and the formulation of adaptation measures. Recommendations are made for enhanced preparedness and resilience. Improved crisis management and areas for future work are suggested.