Runout Characteristics and Grain Size Distribution of Large-scale Debris Flows Triggered by Deep Catastrophic Landslides

The deep Middle Pleistocene subglacial incisions of the Southern North Sea (SNS) are commonly infilled by northward gently dipping clinoforms oriented toward the former ice-sheet core. We have focused on the terminal sector of the largest tunnel valley (TV) of the SNS and offer the first high-resolution reconstruction of the geomorphology and stratigraphy of the infill of the glacial incision, as well as the detailed geomorphology of the incision to better understand the genetic mechanisms of these uncommon but peculiar large-scale (up to 13 km in length) bedforms. For this study, high-resolution 3D seismic data, the grain-size distribution from ditch cutting samples, and the gamma-ray wireline log of borehole K14-12 are used. The TV formed in the subglacial environment by steady state flows in a time-transgressive fashion. Meltwater flow transports the eroded material southward and eventually deposits it at the ice-sheet margin, in the lightly grounded ice-sheet environment where the adverse slope forces the flow to wane. The process results in an elongated ice-margin fan made of clinoforms, whose grain-size distribution fines progressively southward, in the downstream direction. The formation and filling of the TV occurred during the retreat of the ice-sheet margin and cyclic fluctuations of the meltwater mass flow rate, which affected the internal stratigraphy and created an undulated top of the clinoforms’ unit. Sparsely distributed, horizontally layered units interpreted as distal proglacial lacustrine deposits filled depressions on the top of the clinoforms-bearing unit. The sequence was then sealed by a chaotic seismic-stratigraphic unit that probably belongs to postglacial times. The ice-sheet-oriented clinoforms were thus formed by sustained meltwater flow resulting from large-size Scandinavian and British convergent ice sheet flows in the freshwater environment of SNS developed between the complex ice margins and the topographic highs inherited from continental Europe.

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Grain size distribution and topology in 3D grain growth simulation with large-scale Monte Carlo method

International Journal of Minerals Metallurgy and Materials ◽

10.1016/s1674-4799(09)60007-8 ◽

2009 ◽

Vol 16 (1) ◽

pp. 37-42 ◽

Cited By ~ 8

Author(s):

H WANG

Keyword(s):

Grain Size ◽

Monte Carlo ◽

Monte Carlo Method ◽

Size Distribution ◽

Grain Growth ◽

Grain Size Distribution ◽

Large Scale ◽

Growth Simulation ◽

And Topology

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Effects of coarse grain size distribution and fine particle content on pore fluid pressure and shear behavior in experimental debris flows

Journal of Geophysical Research Earth Surface ◽

10.1002/2015jf003725 ◽

2016 ◽

Vol 121 (2) ◽

pp. 415-441 ◽

Cited By ~ 36

Author(s):

Roland Kaitna ◽

Marisa C. Palucis ◽

Bereket Yohannes ◽

Kimberly M. Hill ◽

William E. Dietrich

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Size Distribution ◽

Debris Flows ◽

Fine Particle ◽

Fluid Pressure ◽

Pore Fluid ◽

Coarse Grain ◽

Pore Fluid Pressure ◽

Particle Content

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Downstream evolution of grain size in extremely mobile post-earthquake debris flows, China

10.5194/egusphere-egu21-7389 ◽

2021 ◽

Author(s):

Erin L. Harvey ◽

Tristram C. Hales ◽

Daniel E. J. Hobley ◽

Xuanmei Fan ◽

Jie Liu ◽

...

Keyword(s):

Grain Size ◽

Debris Flow ◽

Size Distribution ◽

Grain Size Distribution ◽

Debris Flows ◽

Fine Fraction ◽

Excess Pore Pressure ◽

Extreme Rainfall Event ◽

2008 Wenchuan Earthquake ◽

Grain Sizes

Large, catchment transitioning debris flows are an important mechanism for transporting sediment from hillslopes into higher order channels. Extremely large flows can exceed volumes of 109 m3, however even flows with volumes of&#160; ~103 m3 can lead to fatalities and extensive damage. Few processes transport a wider range of grain sizes than debris flows, which can transport grains from clays to 10 m boulders. While the structure of debris flows can often be inferred by their deposits, the range of grain sizes presents a challenge for their interpretation. Debris flow grain size distributions can be used to constrain debris flow runout due to their effect on excess pore pressure dissipation. Currently, there is limited data available for the entire grain size distribution of debris flow deposits in the field.We constrained the entire grain size distribution for two extremely large (>1 km in length) post-earthquake debris flows in Sichuan Province, China. These debris flows were triggered in August 2019 after an extreme rainfall event occurred close to the epicentre of the 2008 Wenchuan earthquake. We sampled the debris flows in November 2019 at intervals of 200 m and 500 m, respectively. At each site, we used a combination of field and laboratory sieving to obtain the coarse and fine fraction for both the surface and subsurface. We dug 1 m x 1 m x 0.5 m pits, excavating each layer at 10 cm depth increments. We sieved these increments into five size fractions in the field, including < 1 cm. We sieved 1 kg of the <1 cm fraction in the laboratory to estimate the distribution of the finest grains. The coarse surface fraction was then independently constrained using photogrammetry. Preliminary results for one debris flow show that the distribution of fine grains (~<4 mm) is consistent both laterally and vertically across the runout. This suggests that the processes occurring vertically and laterally during deposition result in the consistent distribution of fines.

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