Role of Rheology Testing in Submarine Debris Flow Simulation-Paper

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The paper presents a systematic method for measuring seabed-soil flow properties and applying them to submarine debris-flow simulations. Because runout, velocity, and flow thickness depend strongly on soil rheology, the authors argue that mapped deposits and estimates of failed volume alone may not reliably describe past events.<br /><br />The method tests field samples with a Brookfield vane-in-cup rheometer, using procedures tailored to potential clay-rich debris flows. Samples are characterized for moisture, density, salinity, plasticity, and shear strength, then tested at in-situ and increased moisture contents. Herschel–Bulkley parameters are fitted to the resulting flow curves. These parameters are incorporated into a depth-averaged, finite-volume model that accounts for the reduced gravity of debris moving underwater.<br /><br />The approach is demonstrated on a relic failure in plastic clay on a steep escarpment at about 600 m water depth. Simulations using measured properties for the soil below the seabed crust reproduced the proximal, blocky deposit reasonably well, with a maximum velocity of about 10 m/s and a duration of under two minutes. A more mobile parameter set produced almost twice the runout and was treated as a conservative upper bound.<br /><br />The simulations did not support the initial interpretation that one large event produced the entire elongated, westward-extending deposit. Matching the distal deposits required unrealistic Bingham-model parameters and resulted in prolonged, very slow movement. The authors therefore interpret the distal lobe as more likely related to separate events, turbidity surges, or post-event sediment reworking.<br /><br />The study concludes that dedicated rheology testing is essential for credible debris-flow risk assessment and that deposit interpretation should account for the possibility of multiple events or flow transformations.

Keywords

submarine debris flow

seabed soil rheology

Brookfield vane rheometer

Herschel-Bulkley model

depth-averaged simulation

clay-rich sediments

runout distance

flow thickness

submarine landslide

debris-flow risk assessment