Magnitude and frequency of debris flows, and areas of hazard on Mount Shasta, northern California

Abstract

Debris flows on Mount Shasta, northern California, have occurred frequently during the late Holocene in response to rapid runoff from melting snow and ice. Glacial-meltwater streams that deeply incise unstable pyroclastic and related flow deposits typically form debris flows when high discharge rates cause slope failures within steep-walled gorges. The landslide material either absorbs streamflow quickly and becomes a slurry or it briefly dams the stream and converts to a debris flow as breaching occurs. All glacial-meltwater streams on Mount Shasta have had repeated debris-flow activity during the last 500 years. During this period, large-magnitude, potentially destructive flows on Mount Shasta have occurred at a rate of four per century, but smaller flows contained by stream channels may be 10 to 20 times more numerous. The smaller debris flows of Mount Shasta pose little hazard to human life or property, whereas larger, out-of-channel flows could cause minor damage. Only the City of McCloud and inhabited areas on the Whitney-Bolam fan appear to be threatened by possible debris-flow activity. None of the streams lacking glacial meltwater have had significant debris-flow activity during late Holocene time. Sediment yields from upper fan areas of Mount Shasta are very high, but most of the sediment moved by debris flows from upper slopes is redeposited on lower fan areas, locally causing extensive and rapid aggradation of the fan surface. Little sediment enters a through-flowing stream network. Correspondingly high denudation rates in the sediment source areas for debris flows (the deep gorges) suggest that a high frequency of debris flows may be unique in recent centuries.

Magnitude–frequency relationships of debris flows — A case study based on field surveys and tree-ring records

“…Despite the practical and theoretical utility of M-F relationships, serious obstacles to obtaining such data and M-F relationships exist and relations have been addressed explicitly in a very limited number of studies to date (e.g., Innes, 1985;Osterkamp et al, 1986;Ohmori and Hirano, 1988;Scott, 1989;Johnson et al, 1991). These studies either based their M-F assessments on rather limited data sets on past events, a vague description of magnitude, or a determination of magnitude at a regional level (van Steijn, 1996).…”

Probability maps of landslide reactivation derived from tree-ring records: Pra Bellon landslide, southern French Alps

“…A more complex analysis of landslide movement involves the interpretation of growth disturbances in annual ring series of trees affected by landslide activity (Carrara and O'Neill, 2003). The earliest dendrogeomorphic studies of landslides date back to Alestalo (1971), and the method has been used ever since extensively in the United States (e.g., Reeder, 1979;Hupp, 1983;Osterkamp et al, 1986;Williams et al, 1992;Carrara and O'Neill, 2003), in Canada (Butler, 1979), but also in Quebec (Bégin and Filion, 1988). In Europe, tree rings have been used to reconstruct the frequency and landslides reactivation in the French (Braam et al, 1987;Astrade et al, 1998) and Italian Alps (Fantucci and McCord, 1995;Fantucci and SorrisoValvo, 1999;Santilli and Pelfini, 2002;Stefanini, 2004), in the Spanish Pyrenees (Corominas and Moya, 1999), and in the Flemish Ardennes (Belgium; Van Den Eeckhaut et al, 2009).…”

Mass movements and tree rings: A guide to dendrogeomorphic field sampling and dating

“…(Image: Google Earth) and fairly accurate date for the production of the minor topographic features a date determined by much counting of annual rings to lie between seventy-five and eighty-five or ninety years ago… More recently, landslide reconstructions started to include GD in annual growth-ring series of trees. The first dendrogeomorphic study of a landslide body dates back to Alestalo (1971), and similar field and laboratory approaches have been used ever since in North America (Shroder, 1978;Butler, 1979b;Reeder, 1979;Hupp, 1983;Jensen, 1983;Osterkamp et al, 1986;Bégin and Filion, 1988;Williams et al, 1992;Carrara and O'Neill, 2003). In Europe, dendrogeomorphic tools were introduced much later to assess the frequency and reactivation of landslides in the French Alps (Braam et al, 1987;Astrade et al, 1998;Lopez Saez et al, 2012a,b), the Italian Apennines (Fantucci and McCord, 1995;Fantucci and Sorriso-Valvo, 1999;Stefanini, 2004), the Spanish Pyrenees (Corominas and Moya, 1999), or the Ardennes (Belgium; Van Den Eeckhaut et al, 2009).…”