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SUMMARY:Frictional hysteresis in granular avalanches - Dr. Chris Johnson (
 University of Manchester)
DTSTART:20220318T123000Z
DTEND:20220318T133000Z
UID:TALK169139@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. Although the general mass and momentum balances that govern such g
 ranular flows have been understood for several decades\, there is still mu
 ch about their behaviour that is poorly understood. In particular\, predic
 ting how far a flow will travel is a significant challenge\, and one of co
 nsiderable practical importance to those living near mountainous regions. 
 In this talk I will use laboratory experiments and models based on the sha
 llow-water equations to demonstrate how flowing granular material can inte
 ract with grains that have already deposited. This interaction profoundly 
 changes the morphology and runout distance of an avalanche. I will show th
 at granular avalanches flowing over an\nerodible layer can flow indefinite
 ly\, by forming a soliton wave that erodes granular material at its front 
 and leaves a trail of deposited grains behind it. In the absence of an ero
 dible layer\, the deposition of grains at the edges of a debris flow or sn
 ow avalanche can confine the subsequent flow laterally\, allow it to flow 
 a much greater distance downslope. The physics underlying these phenomena 
 is the unique frictional rheology of granular materials: when a shear stre
 ss is applied to grains\, they may adopt either a static state or shearing
  state\, with a hysteretic transition between these two behaviours. Incorp
 orating this hysteresis into our model equations allows prediction of a re
 markable amount of the diverse and complex flow behaviour observed in natu
 re.
LOCATION:CUED\, LT6
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