Biographical sketch of a giant: Deciphering recent debris-flow dynamics from the Ohya landslide body (Japanese Alps)

Imaizumi, Fumitoshi; Trappmann, Daniel; Matsuoka, Norikazu; Tsuchiya, Satoshi; Ohsaka, Okihiro; Stoffel, Markus

doi:10.1016/j.geomorph.2015.11.008

Cited by 25 publications

(22 citation statements)

References 59 publications

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“…Examples of the transition from channelized to searching phases on (a–c) the Ohya debris‐flow fan in Japan (images modified from Imaizumi et al. , ; De Haas et al. , ) and (d–f) experimental debris‐flow fan 01.…”

Section: Discussionsupporting

confidence: 92%

“…; Imaizumi et al. ; De Haas et al. ) and in the experiments, the average locus of debris‐flow deposition shifts towards the topographically lower parts of a fan (Figure ).…”

Section: Discussionmentioning

confidence: 99%

“…; Imaizumi et al. ). By way of comparison, avulsions on fluvial fans are often triggered during high flood discharges (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…One outstanding issue is that the spatio‐temporal patterns of deposition on debris‐flow fans have been monitored (Suwa and Okuda, ; Wasklewicz and Scheinert, ; Imaizumi et al. ) or reconstructed (e.g. Helsen et al.…”

Section: Introductionmentioning

confidence: 99%

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Effects of debris‐flow magnitude–frequency distribution on avulsions and fan development

Haas

Kruijt

Densmore

2018

Earth Surf Processes Landf

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Shifts in the active channel on a debris-flow fan, termed avulsions, pose a large threat because new channels can bypass mitigation measures and cause damage to settlements and infrastructure. Recent, but limited, field evidence suggests that avulsion processes and tendency may depend on the flow-size distribution, which is difficult to constrain in the field. Here, we investigate how the flow magnitude-frequency distribution and the associated flow-magnitude sequences affect avulsion on debris-flow fans. We created three experimental fans with contrasting flow-size distributions: (1) a uniform distribution; (2) a steep double-Pareto distribution with many flows around the mean and a limited number of large flows; and (3) a shallow double-Pareto distribution with fewer flows around the mean and more abundant large flows. The fan formed by uniform flows developed through regular sequences of stepwise channelization, backstepping of deposition toward the fan apex, and avulsion over multiple flows. In contrast, the wide range of sizes in the double-Pareto distributions led to distinct avulsion mechanisms and fan evolution. Here, large flows could overtop channels, creating levee breaches that could initiate avulsion immediately or in subsequent events. Moreover, sequences of small-to moderate-sized flows could deposit channel plugs, triggering avulsion in the next large flow. This mechanism was most common on the fan formed by a steep double-Pareto distribution but was rare on the fan formed by a shallow double-Pareto distribution, where large flows were more frequent. We infer that some flow-size distributions are more likely to cause avulsions -especially those that produce abundant sequences of small flows followed by a large flow. Critically, avulsions in our experiments could occur by either large single events or over multiple flows. This observation has important implications for hazard assessment on debris-flow fans, suggesting that attention should be paid to flow history as well as flow size.

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Section: Discussionsupporting

confidence: 92%

“…; Imaizumi et al. ; De Haas et al. ) and in the experiments, the average locus of debris‐flow deposition shifts towards the topographically lower parts of a fan (Figure ).…”

Section: Discussionmentioning

confidence: 99%

“…; Imaizumi et al. ). By way of comparison, avulsions on fluvial fans are often triggered during high flood discharges (e.g.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of debris‐flow magnitude–frequency distribution on avulsions and fan development

Haas

Kruijt

Densmore

2018

Earth Surf Processes Landf

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“…De Haas, Densmore, et al () analyzed the spatiotemporal patterns of debris‐flow fan evolution based on direct field observations (Imaizumi et al, ; Suwa & Okuda, ; Wasklewicz & Scheinert, ) and reconstructions of debris‐flow deposition (e.g., Bollschweiler et al, ; Dühnforth et al, ; Helsen et al, ; Stoffel et al, ; Schürch et al, ; Zaginaev et al, ). They identified two important controls on debris‐flow avulsion that operate over separate time scales.…”

Section: Introductionmentioning

confidence: 99%

Fan‐Surface Evidence for Debris‐Flow Avulsion Controls and Probabilities, Saline Valley, California

et al. 2019

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Debris‐flow fans form by shifts of the active channel, termed avulsions. Field and experimental evidence suggest that debris‐flow avulsions may be induced by depositional lobes that locally plug a channel or superelevation of the channel bed above the surrounding fan surface, by analogy to fluvial fans. To understand debris‐flow avulsion processes, we differentiate between these controls by quantifying the spatial distribution of debris‐flow lobe and channel dimensions, along with channel‐bed superelevation, on nine debris‐flow fans in Saline Valley, California, USA. Channel beds are generally superelevated by 2–5 channel depths above the fan surface, and locally by more than 7 channel depths, thereby substantially exceeding superelevation on fluvial fans. Depositional‐lobe thickness and channel depth decrease with distance from the fan apex, although both are highly variable across the fans. Median channel depths roughly correspond to the 50th–75th percentiles of lobe thicknesses, while minimum channel depths roughly correspond to the 10th–25th percentiles. In contrast, the thicknesses of lobes that have triggered avulsions roughly equal local channel depths and are on average twice as thick as the local median lobe thickness. The spatial correspondence between avulsion locations and thick lobe deposits, and the lack of correlation with channel‐bed superelevation, leads us to infer that avulsions on these fans are mostly caused by thick lobes forming channel plugs. Although results may vary with climatic and tectonic setting, our findings indicate that avulsion hazard assessment on populated fans should include mapping and monitoring of channel depths relative to typical deposit thicknesses on a given fan.

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Debris‐flow fan channel avulsions: An important secondary erosional process along the Ichino‐sawa torrent, Japan

Tsunetaka,

Hotta,

Imaizumi

et al. 2024

Earth Surf Processes Landf

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Sediment transported from debris‐flow initiation zones is typically stored in a topographic feature called a debris‐flow fan, the formation process of which governs secondary sediment transport further downstream. Although sediment transport from debris‐flow fans can impact sediment regimes and change landforms, the determinants of progressive fan formation are not well constrained. To identify such determinants, this study monitored debris flows and performed topographic surveys of debris‐flow fans in the Ichino‐sawa torrent (Japan) during 2016–2017. In this period, eight debris flows occurred, two of which eroded the existing fan and formed a new channel with a short recurrence interval (~40 days). Consequently, these two cases induced substantial sediment transport further downstream from the fan. The examined rainfall indices did not provide a threshold for diagnosing the occurrence of such sediment transport. Debris flows with a large flow depth and a long duration led to changes in the runout direction and subsequently formed new channels. Before these processes, the existing channel was backfilled and plugged by previous debris flows, forming a steep fan surface around the fan apex. The results suggest that increasing the magnitude and the duration of debris flows potentially triggers sediment transport from fans coupled with channel plugging. The annual sediment transport from the fan exceeded almost all sediment yields of the world rivers and was found comparable with that linked with volcanic eruptions and their aftermath. Thus, the fan‐formation process can induce substantial sediment transport, independent of volcanic perturbations and extreme climatic events, and is dependent on the sediment supply from repeated occurrence of debris flows in the initiation zones.

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Biographical sketch of a giant: Deciphering recent debris-flow dynamics from the Ohya landslide body (Japanese Alps)

Cited by 25 publications

References 59 publications

Effects of debris‐flow magnitude–frequency distribution on avulsions and fan development

Effects of debris‐flow magnitude–frequency distribution on avulsions and fan development

Fan‐Surface Evidence for Debris‐Flow Avulsion Controls and Probabilities, Saline Valley, California

Debris‐flow fan channel avulsions: An important secondary erosional process along the Ichino‐sawa torrent, Japan

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