Rainfall-induced lahars in the Belham Valley, Montserrat, West Indies
J. Barclay, J. Alexander, and J. Susnik 2007 Journal of the Geological Society, London v. 164, n. 4, pp. 815-827.
Rain falling on loose volcanic debris over the Soufriere Hills Volcano, Montserrat generates hazardous floods in the Belham Valley. These rainfall-induced lahars vary greatly in discharge and sediment concentration in space and time. They differ from examples documented on other volcanoes in that: (1) the eruption has been continuing since July 1995, generating repeated pulses of excess sediment; (2) rainfall is the only significant trigger; (3) the system is small, with short distance to the sea and relatively low altitude at the catchment top. Repeat mapping and comparison with pre-eruption data demonstrate significant geomorphological change, with c. 120 m shoreline progradation and c. 0.4 m/year mean aggradation rate in the middle to lower valley. The nature of the hazard and area of risk have changed as the valley has aggraded, the channel widened and the runoff efficiency increased (as a result of rilling and vegetation removal). Lahars in the Belham Valley correlate with days when more than 10 mm of rain fell in 24 hours, with more events triggered in the late rainy season. The flows are mainly Newtonian but one non-Newtonian flow event has been demonstrated and is described in detail (20 March 2000). This flow is explained by direct volcanic ash input to the runoff.
Subject: Geoscience:Geology:Geomorphology:Landscape Evolution, Geomorphology as applied to other disciplines, Environmental Science:Natural Hazards, Geoscience:Geology:Geomorphology:Landforms/Processes:Volcanoes, Geoscience:Geology:Sedimentary Geology:Sediment Transport and Deposition, Geoscience:Geology:Igneous and Metamorphic Petrology:Volcanology, Geoscience:Geology:Sedimentary Geology:Sediments and Sedimentary Rocks Resource Type: Scientific Resources:Research Results, Journal Article Special Interest: Hazards
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