Field observations of debris-flow initiation processes on sediment deposits in a previous deep-seated landslide site

Imaizumi, Fumitoshi; Tsuchiya, Satoshi; Ohsaka, Okihiro

doi:10.1007/s11629-015-3345-9

Cited by 23 publications

(25 citation statements)

References 19 publications

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“…2) [Imaizumi et al, 2006]. Sediment infilling of the channels is dominated by a freeze-thaw process that promotes dry ravel and rockfall because of the steep hillslopes [Imaizumi et al, 2006].…”

Section: Study Areamentioning

confidence: 99%

“…1), where the channel bed is alternatively composed of deposited sediments and bedrock. Sediment infilling of the channels is dominated by a freeze-thaw process that promotes dry ravel and rockfall because of the steep hillslopes [Imaizumi et al, 2006].…”

Section: Study Areamentioning

confidence: 99%

“…However, we could not analyze the image from 4:21 to 4:33 because of dark conditions before sunrise. Imaizumi et al [2006] classified the flow phase during debris flow events into two primary types: flows that consist mainly of muddy water (type 1) and flows comprising mainly cobbles and boulders (type 2). Type 1 flows are turbulent and are characterized by black surfaces due to high concentrations of silty sediment sourced from shale.…”

Section: General Characteristics Of Debris Flowsmentioning

confidence: 99%

“…In terms of debris flows caused by transportation of loose sediment on the bottom of valley, both the volume and grain size of debris flow material (e.g., channel deposits, talus slope) change over time and are associated with sediment supply from hillslopes as well as evacuation of the sediment by debris flows and fluvial processes [Bovis and Jakob, 1999;Imaizumi et al, 2006;Berger et al, 2011]. These temporal changes in the debris flow material play important roles in the initiation of the next debris flow [Bovis and Jakob, 1999;Jakob et al, 2005;Chen et al, 2012].…”

Section: Introductionmentioning

confidence: 99%

“…In the debris-flow initiation zone within the Ohya landslide, central Japan, debris flow monitoring has been conducted since 1998 [Imaizumi et al, 2005;Imaizumi et al, 2006]. This area is suitable for debris-flow monitoring because of the high frequency of debris flows (about three or four events per year).…”

Section: Introductionmentioning

confidence: 99%

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Behavior of Boulders within a Debris Flow Initiation Zone

Imaizumi

Tsuchiya

Ohsaka

2016

IJECE

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Although it is important to understand the behavior of debris flows in the initiation zone for the development of mitigative measures, data are scarce due to difficulties in field monitoring. To clarify debris flow behavior within the initiation zone, we established a monitoring system in the upper Ichinosawa catchment within the Ohya landslide, central Japan. In the Ohya landslide, loose sediments, previously deposited on steep channel bed, is the main source of debris flow material. Video image analysis of six debris flows revealed that the largest boulders in the debris flows were usually smaller than those in the channel deposits. Thus, debris flows appear to facilitate the selective transport of channel deposits in the upper Ichinosawa catchment. Flows that occur during debris flow surges can be classified as either i) flows comprising mainly cobbles and boulders, or ii) flows comprising mainly muddy water. The duration of each flow type is different amongst debris flow events. Flows mainly composed of cobbles and boulders accounted for most of the surges when channel deposits, which were the main source of debris flow material, were abundant. In contrast, flows were mainly composed of muddy water in surges when channel deposits were scarce. The particle size of the boulders had no clear relationship with flow height, with the size of the largest boulders generally ranging from 15 to 40 cm regardless of flow heights (ranging 0-5 m). The particle size of the material entrained by the debris flow differed among debris flow events. Coarse particles were frequently found on the flow surface when the particle size of the channel deposits was larger. Therefore, the characteristics of boulders in debris flows within the debris-flow initiation zone were affected by the volume and the size of sediment at the source of the debris flow material.

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Section: Study Areamentioning

confidence: 99%

Section: Study Areamentioning

confidence: 99%

Section: General Characteristics Of Debris Flowsmentioning

confidence: 99%