7.15 Processes, Transport, Deposition, and Landforms: Flow

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Abstract

Flows on hillslopes are high gradient, free-surface mass movements of grain-in-fluid materials. They are generally initiated as slides by high pore-water pressures and rapidly transform into non-Newtonian, unsteady, and nonuniform (surging) flows that commonly form their own channels by constructing levees. Deposition or entrainment of material during flow may be very significant. Flows are characteristically nonturbulent in nature, but grain-in-fluid motion is difficult to analyze and numerical simulation appears to hold the best prospect of runout prediction if the flow volume and material characteristics can be estimated; however, extreme sensitivity to water content is a problem.

Debris flows consist of large clasts moving in a slurry of fine material in water; they can be very destructive, with large surges carrying boulders at the front of the surge. Their deposits are generally lobate, with large surface boulders indicating the ability of debris flows to transport everything available.

Earth flows are generally large, fine-grained, long-lasting features that move slowly in response to rainfall and increased pore-water pressure. They commonly form extensive complexes. A low-gradient, rapid, and very dangerous variety forms because of instability in sensitive clays causing regressive collapse; earth-flow-like features have also been recorded in submarine environments.

Peat flows follow the detachment of peat bodies wholly or partly from the underlying substrate. The distinctive properties and rheology of peat result in activities quite different from that of normal hillslope materials and can generate significant hazards both downslope and down channel.

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    Hummocks are mounds, blocks and ridges that characterize large landslides and debris/rock avalanches (Paguican et al., 2014; Shea and van Wyk de Vries, 2008; Siebert, 1984; Ui, 1983; Yoshida et al., 2012). Hummocks result from the formation of horsts and grabens during transport and spreading or by stretching around blocks by faults (Davies et al., 2013; Glicken, 1996; Glicken et al., 1981; Shea et al., 2008; Voight et al., 1981), and their shapes can be used to determine the kinematics of a landslide (Shea and van Wyk de Vries, 2008). Hummocks in debris/rock-avalanche deposits are characterised by pervasive shattering or jigsaw fracturing as result of brittle deformation associated with the transport of large rock masses (e.g., Calvari et al., 1998; Shreve, 1968; Ui et al., 1986; Yarnold and Lombard, 1989).

Tim Davies is presently an associate professor of geological sciences at the University of Canterbury, New Zealand. His PhD in civil engineering was awarded by the University of Southampton, UK in 1973. In his career, he has specialized in river mechanics, debris flows, rock avalanches, and rock fracture processes, and he now leads the Hazard and Disaster Management postgraduate programs at the University of Canterbury.

Chris Phillips is a senior scientist in soils and landscape processes at Landcare Research, Christchurch, New Zealand. He has 30 years of research experience in the fields of erosion processes, how vegetation mitigates erosion, and, more recently, in integrated catchment management. He now describes himself as a generalist. He obtained his PhD in agricultural engineering from the University of Canterbury in 1989 and earlier degrees from Otago and Waikato universities. In the early part of his career, he worked for the New Zealand Forestry Research Institute studying the relationship between geology and geomorphology and the implications for forest management in the East Coast region of New Zealand. Latterly, he has been involved in a 10-year interdisciplinary study that recently ended, focused on the Motueka River catchment and its connection to Tasman Bay, in the northern part of South Island, New Zealand.

Jeff Warburton's research is concerned primarily with understanding the geomorphology and sediment-transfer processes operating in upland and mountain catchments. Particular emphasis is placed on upland peat erosion, peat mass movements, debris flows/shallow landslides, glacio-fluvial sediment transfer, and the geomorphology of mountain streams. This work is underpinned by intensive field monitoring programs and geomorphological laboratory experiments.

Jeff has served on the Executive Committee of the British Geomorphological Research Group and together with Dave Higgitt was joint-chair of the BGRG Working Group on Upland Sediment Budgets. In 2000, he was made a Millennium fellow for his work on ‘Understanding the landscape of the North Pennines’.

Davies, T., Phillips, C., Warburton, J., 2013. Processes, transport, deposition, and landforms: flow In: Shroder, J. (Editor in Chief), Marston, R.A., Stoffel, M. (Eds.), Treatise on Geomorphology. Academic Press, San Diego, CA, vol. 7, Mountain and Hillslope Geomorphology, pp. 158–170.

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