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Can you stop a PDC? Assessing the impact of vertical topographic barriers on channelised, aerated, dense granular currents

Jordan Chenery1 , Rebecca Williams2, Natasha Dowey3, Pete Rowley4, Rob Thomas1

  • Affiliations: 1Energy and Environment Institute, University of Hull, Hull, UK; 2School of Environmental Sciences, University of Hull, Hull, UK; 3Department of the Natural and Built Environment, Sheffield Hallam University, Sheffield, UK; 4School of Earth Sciences, University of Bristol, Bristol, UK 

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 169

  • Programme No: 3.9.8

  • Theme 3 > Session 9

Abstract

Pyroclastic density currents (PDCs) are hazardous volcanic flows that have the potential to surmount topographic highs. Topography can deflect or reflect PDCs and topographic barriers are sometimes used to delineate inundation areas in hazard assessment. However, how PDCs interact with topography is not well understood. Past experimental studies have found that all (or part) of a dilute current can overtop topography, depending on the height of the barrier with respect to current thickness and the momentum of the flow. The effect of topography on the basal granular layer of a PDC has not previously been investigated. Here, we quantify the effects of different vertical topographic barriers (varying in height and barrier position relative to the current source) on flow velocity, runout length and the behaviour of aerated dense-granular currents (analogous to dense granular PDCs) in an experimental flume. Short lived (<3 s) currents are allowed to propagate downstream from source and impact the barriers. Our results show that the nature of current interaction with a barrier is dependent upon the ratio of barrier height to current thickness (hbarrier/hcurrent). For instance, values of hbarrier/hcurrent of <~2.7 result in the arriving current lifting off and following a ballistic trajectory as it overtops the barrier. Our results indicate a linear trend between normalised runout length and hbarrier/hcurrent, and suggest that a vertical barrier needs to be ~4.8 times higher than current thickness to block a channelised dense, granular current. Future analysis will focus on depositional processes and resultant analogue deposits.