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SUMMARY:Frictional hysteresis in granular avalanches - Dr. Chris Johnson (
 University of Manchester)
DTSTART:20220128T123000Z
DTEND:20220128T133000Z
UID:TALK166918@talks.cam.ac.uk
CONTACT:99736
DESCRIPTION:Debris flows and snow avalanches are typical of a wide range o
 f natural hazards in which grains of rock\, ice or snow are eroded from a 
 mountain slope and flow rapidly downhill\, eventually stopping to form a d
 eposit.\nAlthough the general mass and momentum balances that govern such 
 granular flows have been understood for several decades\, there is still m
 uch about their behaviour that is poorly understood. In particular\,\npred
 icting how far a flow will travel is a significant challenge\, and one of 
 considerable practical importance to those living near mountainous regions
 . In this talk I will use laboratory experiments and models based on the s
 hallow-water equations to demonstrate how flowing\ngranular material can i
 nteract with grains that have already deposited. This interaction profound
 ly changes the morphology and runout distance of an avalanche. I will show
  that granular avalanches flowing over an\nerodible layer can flow indefin
 itely\, by forming a soliton wave that erodes granular material at its fro
 nt and leaves a trail of deposited grains behind it. In the absence of an 
 erodible layer\, the deposition of grains at the edges of a debris flow or
  snow avalanche can confine the subsequent flow laterally\, allow it to fl
 ow a much greater distance downslope. The physics underlying these phenome
 na is the unique frictional rheology of granular materials: when a shear s
 tress is\napplied to grains\, they may adopt either a static state or shea
 ring state\, with a hysteretic transition between these two behaviours. In
 corporating this hysteresis into our model equations allows prediction of 
 a remarkable amount of the diverse and complex flow behaviour\nobserved in
  nature.
LOCATION:CUED\, LR3A
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