Periglacial debris-flow initiation and susceptibility and glacier recession from imagery, airborne LiDAR, and ground-based mapping

Abstract

Climate changes in the Pacifi c Northwest, USA, may cause both retreat of alpine glaciers and increases in the frequency and magnitude of storms delivering rainfall at high elevations absent signifi cant snowpack, and both of these changes may affect the frequency and severity of destructive debris fl ows initiating on the region's composite volcanoes. A better understanding of debrisfl ow susceptibility on these volcanoes' slopes is therefore warranted. Field mapping and remote sensing data, including airborne light detection and ranging (LiDAR), were used to locate and characterize initiation sites of six debris fl ows that occurred during an "atmospheric river" event (warm wet storm) on Mount Rainier, Washington, in November 2006, and data from prior studies identifi ed six more debris fl ows that occurred in 2001-2005. These 12 debris fl ows had initiation sources at the heads of 17 gullies distributed over seven distinct initiation zones near the termini of glaciers, and all debris-fl ow initiation sites were located within areas exposed by glacier retreat in the past century. Gully locations were identifi ed by their steep walls and heads on a 1-m digital elevation model (DEM) from LiDAR data collected in 2007-2008. Gullies in which debris fl ows initiated were differentiated from numerous non-initiating gullies primarily by the greater upslope contributing areas of the former. Initiation mechanisms were inferred from pre-and post-2006 gully width measurements from aerial photos and the LiDAR DEM, respectively, fi eld observations of gully banks, and elevation changes calculated from repeated LiDAR, and these data indicate that debris fl ows were initiated by distributed sources, including bank mass failures, related to ero-sion by overland fl ow of water. Using gullyhead initiation sites for debris fl ows that occurred during 2001-2006, a data model was developed to explore the viability of the method for characterization of debris-fl ow initiation susceptibilities on Mount Rainier. The initiation sites were found to occupy a restricted part of the four-dimensional space defi ned by mean and standard deviation of simulated glacial meltwater fl ow, slope angle, and minimum distance to an area of recent (1994-2008) glacier retreat. The model identifi es the heads of most gullies, including all sites of known debris-fl ow initiation, as highsusceptibility areas, but does not appear to differentiate between areas of varying gullyhead density or between debris-fl ow and no-debris-fl ow gullies. The model and fi eld data, despite limitations, do provide insight into debris-fl ow processes, as well as feasible methods for mapping and assessment of debris-fl ow susceptibilities on periglacial areas of the Cascade Range.

Data Mining and Statistical Approaches in Debris-Flow Susceptibility Modelling Using Airborne LiDAR Data

“…From, the thorough review of relevant literatures e.g., [38,60,115,149,150,151,152,153,154,155] twelve conditioning factors were selected and they were derived from the 2 m LiDAR DEM. These factors include; elevation (Figure 3a), plane curvature (Figure 3b), slope angle (Figure 3c), total curvature (Figure 3d), slope aspect (Figure 3e), Sediment Transport Index (STI) (Figure 3f), topographic profile curvature (Figure 3g), Topographic Roughness Index (TRI) (Figure 3h), flow accumulation/SCA (Figure 3i), Stream Power Index (SPI) (Figure 3j), Topographic Wetness Index (TWI) (Figure 3k), and Topographic Position Index (TPI) (Figure 3l).…”

Effective Hydrological Events in an Evolving Mid‐latitude Mountain River System Following Cataclysmic Disturbance—A Saga of Multiple Influences

“…Such events effectively deliver great amounts of rainfall to geographically focused regions. These “firehoses” of tropical moisture can last several days and, when augmented by snowmelt, are a key mechanism causing substantial flooding and debris flows in the western coastal United States (Burns et al., 2015; Lancaster et al., 2012; Li et al., 2019; Mosbrucker et al., 2019; Ralph & Dettinger, 2011; Ralph et al., 2006; Sobieszczyk et al., 2008).…”

Debris flow initiation in proglacial gullies on Mount Rainier, Washington

“…Material released during channel and gully expansion provides sediment that has been connected with progressive transformation of overland flow to debris flow (Gabet and Bookter, 2008). Whereas glaciated catchments do not experience analogous changes in infiltration capacity, gullies often expand through recently deglaciated and unchannelized surfaces (O'Connor et al, 2001;Lancaster et al, 2012). It is therefore plausible that these young gullies actively expand during the largest storms in a manner similar to gullies in recently burned areas.…”

“…Recent observations on Mount Rainier (Washington, USA) suggest that debris flow initiation has occurred in gullies passing through areas dominated by loose glacial till. These gullies show evidence of wall collapse and lateral expansion along their lengths, which may represent a source of sediment for the debris flows (Copeland, 2009;Lancaster et al, 2012). Gullies also begin at or very near to glacier termini and have no apparent slope failures that could have contributed debris flows from upstream glacier surfaces.…”