Landslides control the spatial and temporal variation of channel width in southern Taiwan: Implications for landscape evolution and cascading hazards in steep, tectonically active landscapes. Issue 9 (13th March 2018)

• Record Type: Journal Article
• Authors: Yanites, Brian J.; Mitchell, Nate A.; Bregy, Joshua C.; Carlson, Grace A.; Cataldo, Kirstyn; Holahan, Margaret; Johnston, Graham H.; Nelson, Amelia; Valenza, Jeffery; Wanker, Matthew
• Is Part Of: Earth surface processes and landforms. Volume 43:Issue 9(2018)
• Page Start: 1782
• Page End: 1797
• Publication Date: 2018-03-13
• Subjects: landslides -- fluvial geomorphology -- channel width -- tectonic geomorphology -- hazards; Geomorphology -- Periodicals; 551.4
• DOI: 10.1002/esp.4353
• Languages: English
• ISSNs: 0197-9337

Abstract

Abstract: Intense precipitation or seismic events can generate clustered mass movement processes across a landscape. These rare events have significant impacts on the landscape, however, the rarity of such events leads to uncertainty in how they impact the entire geomorphic system over a range of timescales. Taiwan is steep, tectonically active, and prone to landslide and debris flows, especially when exposed to heavy rainfall events. Typhoon Morakot made landfall in Taiwan in August of 2009, causing widespread landslides in southern Taiwan. The south to north trend in valley relief in southern Taiwan leads to spatial variability in landslide susceptibility providing an opportunity to infer the long‐term impact of such landslide events on channel morphology. We use pre‐ and post‐typhoon imagery to quantify the propagating impact of this event on channel width as the debris is routed through the landscape. The results show the importance of cascading hazards from landslides on landscape evolution based on patterns of channel width (both pre‐ and post‐typhoon) and hillslope gradients in 20 basins along strike in southern Taiwan. Prior to Typhoon Morakot, the river channels in the central part of the study area were about 3–10 times wider than the channels in the south. Following the typhoon, aggradation and widening was also a maximum in these central to northern basins where hillslope gradients and channel steepness is high, accentuating the pre‐typhoon pattern. The results further show that the narrowest channels are located where channel steepness is the lowest, an observation inconsistent with a detachment‐limited model for river evolution. We infer this pattern is indicative of a strong role of sediment supply, and associated landslide events, on long‐term channel evolution. These findings have implications across a range of spatial and temporal scales including understanding the cascade of hazards in steep landscapes and geomorphic interpretation of channel morphology. Copyright © 2018 John Wiley & Sons, Ltd. Abstract : A comparison of channel morphology before and after Typhoon Morakot shows that landslides influence channel morphology in southern Taiwan. Even prior to the typhoon, channels were widest where hillslopes and river slopes were greatest. This pattern of channel width was accentuated by aggradation and widening due to the propagation of landslide debris through the drainage basin.