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Hyperconcentrated flow in nature and in practical application
Published in Zhaohui Wan, Zhaoyin Wang, Hyperconcentrated Flow, 2020
Debris flow is a kind of hyperconcentrated flow. It carries large amounts of granular particles with wide size composition, from large stones to clay particles, and its density may reach 1.9–2.2 g/cm3. The velocity of debris flow can be rather high. The maximun recorded velocity in China is 13.4 m/s (Zhang & Yuan, 1980). Hence it is a powerful destructive force and threatens railways, highways, lives and the property of local citizens. Volcanic debris flows and other hypercon-centrated flows resulting from them have been observed and studied by Scott & Dinehart (1985). Volcanic debris flows are named as lahars. And the hypercon-centrated streamflow following lahar is named as lahar-runout flow. Lahars are formed in the following ways: By the bulking of lake-breakout flood surges with eroded alluvium;From flood surges produced from snowmelt by hot lithic pyroclastic;From material catastrophically ejected and mixed with water of hydrothermal and glacial or snowmelt origin.
Area sources
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
A dangerous side effect of the ash fall is that when wetted it can cause dangerous mud flows called lahars. Lahars are caused by the wetting of unstable ash and other debris. Once the mixture is saturated with water, it flows very fast down the flanks of the volcanoes. Lahars can be very destructive and on 19 May there was a lahar in the Svaðbælisheiði river (Jenkins, 2010). In fact, the main environmental effect of the ash cloud may end up being some cooling of the northern hemisphere. This effect is due to the sunlight being blocked out, not by the ash, but by the sulphur aerosols. This may have a knock-on effect of less biomass growth for a few years.
Volcanic activity
Published in F.G. Bell, Geological Hazards, 1999
A lahar is a flowing slurry of volcanic debris and water that originates on a volcano. Lahars in which 50% of the volcanic debris is of sand size or smaller are termed mudflows. Beverage and Cuthbertson (1964) regarded lahars as water—sediment mixtures in which the volcanic debris accounts for 40 to 80% by weight, and which may move by turbulent flow. As the proportion of debris increases, laminar flow replaces turbulent flow.
A review of lahars; past deposits, historic events and present-day simulations from Mt. Ruapehu and Mt. Taranaki, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Jonathan Procter, Anke Zernack, Stuart Mead, Michael Morgan, Shane Cronin
The Indonesian term ‘lahar’ is commonly used to describe a volcanic mudflow originating from the steep flanks of the volcanic edifice. Usually, the event is triggered by volcanic heat that melts snow and ice, a dam break from a crater lake or rainfall runoff remobilising or eroding deposited volcaniclastics (Scott 1988). Smith and Fritz (1989) define the term as ‘a rapidly flowing mixture of rock debris and water (other than normal streamflow) from a volcano’. Pierson and Costa (1987) recognise that water-sediment ratios in lahars are highly variable in various settings and that their rheological characteristics are furthermore strongly influenced by other factors such as grainsize, velocity, topography and temperature.