Periglacial Debris-Flow Initiation and Susceptibility and Glacier Recession
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Seeing the True Shape of Earth’s Surface: Applications of Airborne and Terrestrial Lidar in the Geosciences themed issue Periglacial debris-fl ow initiation and susceptibility and glacier recession from imagery, airborne LiDAR, and ground-based mapping Stephen T. Lancaster1,*, Anne W. Nolin1, Elizabeth A. Copeland1, and Gordon E. Grant2 1College of Earth, Ocean, and Atmospheric Sciences and Institute for Water and Watersheds, Oregon State University, Corvallis, Oregon 97331, USA 2U.S. Department of Agriculture Forest Service, Pacifi c Northwest Research Station, 333 SW First Avenue, Corvallis, Oregon 97331, USA ABSTRACT sion by overland fl ow of water. Using gully- et al., 1996; O’Connor et al., 2001; Osterkamp head initiation sites for debris fl ows that et al., 1986; Sobieszczyk et al., 2009; Walder Climate changes in the Pacifi c Northwest, occurred during 2001–2006, a data model and Driedger, 1994). USA, may cause both retreat of alpine gla- was developed to explore the viability of the There is concern among managers and ciers and increases in the frequency and method for characterization of debris-fl ow policymakers that glacier retreat, rising snow- magnitude of storms delivering rainfall at initiation susceptibilities on Mount Rainier. line elevations, and more frequent and more high elevations absent signifi cant snowpack, The initiation sites were found to occupy a intense storms are leading to greater debris- and both of these changes may affect the restricted part of the four-dimensional space fl ow hazards. On Washington’s Mount Rainier frequency and severity of destructive debris defi ned by mean and standard deviation of in August 2001, rapid melting of Kautz Glacier fl ows initiating on the region’s composite simulated glacial meltwater fl ow, slope angle, directed meltwater into the adjacent watershed volcanoes. A better understanding of debris- and minimum distance to an area of recent of Van Trump Creek, incised a new channel, and fl ow susceptibility on these volcanoes’ slopes (1994–2008) glacier retreat. The model iden- led to initiation of a series of debris fl ows, which is therefore warranted. Field mapping and tifi es the heads of most gullies, including all formed a new debris fan in the Nisqually River remote sensing data, including airborne light sites of known debris-fl ow initiation, as high- near the main road into Mount Rainier National detection and ranging (LiDAR), were used to susceptibility areas, but does not appear to Park (Vallance et al., 2002; Vallance et al., locate and characterize initiation sites of six differentiate between areas of varying gully- 2003). In November 2006, an “atmospheric debris fl ows that occurred during an “atmo- head density or between debris-fl ow and river” event (Neiman et al., 2008), i.e., a storm spheric river” event (warm wet storm) on no-debris-fl ow gullies. The model and fi eld track carrying warm, moist air from the tropics, Mount Rainier, Washington, in November data, despite limitations, do provide insight produced heavy rainfall at high elevations with 2006, and data from prior studies identifi ed into debris-fl ow processes, as well as fea- little antecedent snowpack and triggered debris six more debris fl ows that occurred in 2001– sible methods for mapping and assessment fl ows and fl ooding that caused major damage 2005. These 12 debris fl ows had initiation of debris-fl ow susceptibilities on periglacial to infrastructure, particularly on Mount Hood sources at the heads of 17 gullies distributed areas of the Cascade Range. in Oregon and Mount Rainier in Washington. over seven distinct initiation zones near the In this study, we use the data from debris fl ows termini of glaciers, and all debris-fl ow initia- INTRODUCTION that occurred on Mount Rainier in 2001–2006 tion sites were located within areas exposed to improve our understanding of the relevant by glacier retreat in the past century. Gully The rapidly moving slurries of mud, rocks, processes and as the basis for an attempt to map locations were identifi ed by their steep walls water, and wood known as debris fl ows present and model debris-fl ow initiation susceptibilities, and heads on a 1-m digital elevation model hazards in mountainous areas around the world. a preliminary step toward quantifying hazards (DEM) from LiDAR data collected in 2007– The nature and severity of those hazards may be on that mountain. 2008. Gullies in which debris fl ows initiated changing as the variables affecting the process The destructive potential of landslides and were differentiated from numerous non-initi- itself, such as climate and glacier extent, and debris fl ows has motivated previous attempts ating gullies primarily by the greater upslope the human interaction with that process both to assess the hazards posed by these mass- contributing areas of the former. Initiation change. Climate change may bring an intensi- movement processes. Hazards from large lahars mechanisms were inferred from pre- and fi cation of storms, and increasing temperatures (debris fl ows originating on volcanoes) induced post-2006 gully width measurements from are responsible for the retreat of alpine glaciers by active volcanism have been mapped for aerial photos and the LiDAR DEM, respec- (Oerlemans, 1994). Expansion of human settle- Mount Rainier based on an empirical relation- tively, fi eld observations of gully banks, and ments and other infrastructure into mountainous ship between volume and inundation area (Gris- elevation changes calculated from repeated areas may increase communities’ exposure to wold and Iverson, 2008; Iverson et al., 1998), but LiDAR, and these data indicate that debris potentially destructive debris fl ows. In the Cas- such mapping provides little information regard- fl ows were initiated by distributed sources, cade Range of the Pacifi c Northwest, proglacial ing smaller meltwater- and storm-induced lahars. including bank mass failures, related to ero- areas on composite volcanoes are typically steep Models based on steady-state hydrology and the and mantled with ample unconsolidated material effects of pore pressures on slope stability pro- *[email protected] and are therefore prone to debris fl ows (Blodgett vide maps of relative susceptibility to shallow Geosphere; April 2012; v. 8; no. 2; p. 417–430; doi:10.1130/GES00713.1; 8 fi gures; 4 tables. For permission to copy, contact [email protected] 417 © 2012 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/2/417/3343034/417.pdf by guest on 01 October 2021 Lancaster et al. rapid landsliding and associated debris fl ows digital topography. Evolving technology for MOUNT RAINIER IN THE (Dietrich et al., 1995; Miller and Burnett, 2007, airborne laser swath mapping, or light detection WASHINGTON CASCADES 2008; Montgomery and Dietrich, 1994), and and ranging (LiDAR), evolving methods for models based on transient hydrology form the production of high-resolution “bare-earth” digi- With its summit at 4393 m, Mount Rainier basis for forecasting debris fl ow hazards due to tal topography, and advancing efforts to collect is the tallest volcano in the Cascade Range individual storms (Chleborad et al., 2008; Iver- these data present new opportunities for hazard of Washington, Oregon, and California. The son, 2000), but the periglacial debris fl ows on and susceptibility mapping. upper slopes of Mount Rainier are composed of Mount Rainier appear to be largely initiated by In our overarching research question, we ask unconsolidated Quaternary-age volcani clastic overland fl ow of water that leads to distributed whether recent glacier retreat in the Cascades and morainal material in steep edifices. The gullying and associated bank slumping rather has exposed areas with relatively high suscepti- slopes also contain numerous glaciers and than by localized landslides (Copeland, 2009; bility to debris-fl ow initiation, and if so, do these perennial bodies of snow and ice, as well Vallance et al., 2002). Despite recent observa- additional areas compose a large fraction of as debris-covered stagnant ice masses of tions of debris fl ows on Mount Rainier (Vallance high-susceptibility areas on the steep composite unknown spatial extent (C. Driedger, 2008, et al., 2002) and other areas with debris fl ows volcanoes of the Cascades. More specifi cally, personal commun.). Mount Rainier is drained initiated by overland fl ow (McCoy et al., 2010), this paper explores whether data from remote by fi ve major glacier meltwater-fed braided we still lack a method for determining relative sensing and fi eld mapping might provide a basis rivers (Fig. 1), the headwaters of which are hazards in areas prone to such events. for debris-fl ow susceptibility mapping, which is located within canyons, often 300–900 m deep, While fi eld-based monitoring is leading to necessary in order to answer the larger question formed by lateral moraines from Pleistocene greater understanding of debris fl ows triggered regarding increased hazard and risk associated glaciers below adjacent ridges (Crandell, 1971). by intense rain and overland fl ow (McCoy et al., with glacier retreat. Here, we map debris-fl ow Stream gradients on the upper fl anks of the 2010), advances in remote sensing provide initiation sites with fi eld- and remote sensing– mountain, above tree line, are 0.13–0.15 and, opportunities for addressing the relative suscep- based methods, determine limits of debris-free at the confl uence with major rivers near park tibility to overland fl ow-induced events at the glacier ice and characterize topography with boundaries, 0.019–0.078 (Crandell, 1971). Tree landscape scale. Many hazard and susceptibility remote sensing–based methods, and demon- line is located at elevations in the range 1600 mapping efforts in the past were somewhat lim- strate preliminary data-based modeling of areas to 2000 m; forests cover over 56% of Mount ited by the coarse resolution of readily available susceptible to debris-fl ow initiation.