Alpine Debris Flows in Northern Scandinavia. Morphology and Dating by Lichenometry

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. ABSTRACT. The effects of an extreme rainfall triggering debris flows (mudflows) in the mountains S of Abisko, N Sweden, in 1979, are evaluated with regard to geomorphological impact. Several older events of debris flows in the same area during postglacial time are evident in the morphology of the slopes. Where such flows have occurred repeatedly, debris accumulations superficially similar to alluvial cones and referred to as debris flow cones are built. An attempt at dating old flows by means of lichenometry indicated at least four earlier events within the last 2700 years in Nissunvagge. A map of the spatial pattern of known rainfall-triggered mass movements in northern Lappland is presented to support the hypothesis of geomorphic impact of extreme rainfall in three area size classes called regions, cells and spots. in Nissunvagge area, N. Sweden. Key: I = Mountain ridge and summit with altitude in meters. 2 = Stream. 3 = Glacier. 4 = Sediment plume in Lake Tornetrask. 5 = Lake. 6 = Railway. 7 = Each arrow shows one large debris flow or a group of smaller ones. 8 = Alluvial fan in valley bottom affected by debris flow flood. Note difference between debris flows deposited as colluvium on U-valley slopes, and those removed by stream flood, at the base of V-valley slopes. The latter arrows reach the streams. ALPINE DEBRIS FLOWS IN NORTHERN SCANDINAVIA Fig. 2. Photograph of section C, Nissunvagge, one month after the debris flows in 1979. Fresh debris flows C20 (left) to C42 (right) appear as white tracks on dark talus slopes and colluvial fans. Valley bottom at 900 m altitude with tundra polygons. Mountain top at 1640 m altitude. Photo N. A. Andersson, 25.7.1979.

Effects of the Little Ice Age on avalanche boulder tongues in the French Alps (Massif des Ecrins)

“…A very large range of processes and slope deposits have been studied. Previous works on this topic were mostly on debris flows (Rapp and Nyberg, 1981;Innes, 1985b;Van Steijn, 1996), rock glaciers (Evin and de Beaulieu, 1985;Haeberli, 1985;Evin, 1987;Hamilton and Whalley, 1995;Humlum, 1996Humlum, , 1999Haeberli and Beniston, 1998;Francou et al, 1999), and rock avalanches (Grove, 1972(Grove, , 1988Porter and Orombelli, 1980). Lichenometric measurements (Gray, 1973;Innes, 1985b;Luckman and Fisk, 1995;McCarroll et al, 1998), dendrochronological observations (Hétu, 1990;Lafortune et al, 1997) or sedimentation rates (Kotarba et al, 1987;André, 1997;Blikra and Selvik, 1998) show that climatic changes, which occurred since the Little Ice Age, induce diachronous variations in slope processes.…”

Distribution of debris flows in Glacier National Park, Montana, U.S.A.

“…Many investigations in mountainous areas concern mass-wasting events initiated by intense rainfall; these studies suggest that these events are responsible for a majority of the geomorphic work in steep terrain (e.g. Caine 1980, Rapp and Nyberg 1981, Luckman 1992, Krautblatter 2003. Summer thunderstorms have been documented as initiating debris flows in individual drainage basins within Glacier National Park (Butler and Malanson 1996).…”

Catastrophic middle Pleistocene jökulhlaups in the upper Susquehanna River: Distinctive landforms from breakout floods in the central Appalachians

“…This situation, combined with a likely high volume of ice in both the lake water and ice incorporated along the flow route from the catastrophically disintegrating glacial dam, may have provided a mechanism for rapid emplacement of these sediment-charged, slushy flows on these low gradients. It is also possible that warming during the glacial disintegration may have triggered widespread hillslope water and sediment additions to the lakes in the form of flows similar to the slush avalanches described in high latitude periglacial regions (Rapp and Nyberg, 1981;Nyberg, 1989). In any case, the jökulhlaup flows appear to have been similar to viscous debris flows but moving on an extraordinarily low gradient.…”