Debris-flow deposition: Effects of pore-fluid pressure and friction concentrated at flow margins

Measurements of pore-fluid pressure and total bed-normal stress at the base of several similar to 10 m(3) experimental debris flows provide nem insigh t into the process of debris-now deposition. Pore-fluid pressures nearly su fficient to cause Liquefaction were developed and maintained during now mob ilization and acceleration, persisted in debris-flow interiors during flow deceleration and deposition, and dissipated significantly only during postd epositional sediment consolidation. In contrast, leading edges of debris fl ows exhibited little or no positive pore-fluid pressure. Deposition therefo re resulted from grain-contact friction and bed friction concentrated at fl ow margins. This finding contradicts models that invoke widespread decay of excess pore-fluid pressure, uniform viscoplastic yield strength, or pervas ive grain-collision stresses to explain debris-now deposition. Furthermore, the finding demonstrates that deposit thickness cannot be used to infer th e strength of flowing debris.