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Abrupt transitions in gravity currents

Abrupt transitions in gravity currents
Abrupt transitions in gravity currents
Pyroclastic flows and snow avalanches sometimes exhibit a rapid deceleration of their dense flow fronts and detachment of their dilute clouds. This behavior is also inferred for submarine flows and could explain stepped thickness patterns in their deposits. A similar “abrupt transition” process occurs in particle-laden, lock release laboratory currents with relatively high concentrations. New experiments on nonparticulate, solute-driven density currents were run to investigate the cause of abrupt transitions. Abrupt transitions occur in laboratory currents with Reynolds numbers (Re) less than 1000 and are interpreted, supported by theoretical scaling analysis, to signify a change in dynamic regime. Currents with high Re, which do not show abrupt transitions, undergo a downstream change in dynamic regime from (1) inertial slumping to (2) inertial-buoyancy spreading to (3) viscous-buoyancy spreading. In low Re currents that undergo abrupt transitions, however, the duration of the second regime is very short, and hence they appear to pass directly from the quickly moving slumping phase into the slowly moving viscous phase. Scaling analysis indicates that an abrupt transition should occur in currents below a critical value of Re of ?10–5000 for currents with different initial aspect ratios. Given that natural flows typically have greater Reynolds numbers, we suggest that abrupt transitions in laboratory and natural currents are likely to be dynamically different. This work has important implications for the physical modeling of gravity flows.
gravity currents, flow transformation, turbidity currents, debris flows, pyroclastic flows, snow avalanches
0148-0227
F03001
Amy, L.A.
ef602b7f-ef4e-4cba-96e7-e34096eb3066
Hogg, A.
affd474d-4b53-49cc-a57f-54b2a1e5c02d
Peakall, J.
2351dbf6-2c4f-4250-bacf-fe1b69870f26
Talling, P.T.
1cbac5ec-a9f8-4868-94fe-6203f30b47cf
Amy, L.A.
ef602b7f-ef4e-4cba-96e7-e34096eb3066
Hogg, A.
affd474d-4b53-49cc-a57f-54b2a1e5c02d
Peakall, J.
2351dbf6-2c4f-4250-bacf-fe1b69870f26
Talling, P.T.
1cbac5ec-a9f8-4868-94fe-6203f30b47cf

Amy, L.A., Hogg, A., Peakall, J. and Talling, P.T. (2005) Abrupt transitions in gravity currents. Journal of Geophysical Research, 110, F03001. (doi:10.1029/2004JF000197).

Record type: Article

Abstract

Pyroclastic flows and snow avalanches sometimes exhibit a rapid deceleration of their dense flow fronts and detachment of their dilute clouds. This behavior is also inferred for submarine flows and could explain stepped thickness patterns in their deposits. A similar “abrupt transition” process occurs in particle-laden, lock release laboratory currents with relatively high concentrations. New experiments on nonparticulate, solute-driven density currents were run to investigate the cause of abrupt transitions. Abrupt transitions occur in laboratory currents with Reynolds numbers (Re) less than 1000 and are interpreted, supported by theoretical scaling analysis, to signify a change in dynamic regime. Currents with high Re, which do not show abrupt transitions, undergo a downstream change in dynamic regime from (1) inertial slumping to (2) inertial-buoyancy spreading to (3) viscous-buoyancy spreading. In low Re currents that undergo abrupt transitions, however, the duration of the second regime is very short, and hence they appear to pass directly from the quickly moving slumping phase into the slowly moving viscous phase. Scaling analysis indicates that an abrupt transition should occur in currents below a critical value of Re of ?10–5000 for currents with different initial aspect ratios. Given that natural flows typically have greater Reynolds numbers, we suggest that abrupt transitions in laboratory and natural currents are likely to be dynamically different. This work has important implications for the physical modeling of gravity flows.

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More information

Published date: 2005
Keywords: gravity currents, flow transformation, turbidity currents, debris flows, pyroclastic flows, snow avalanches

Identifiers

Local EPrints ID: 54755
URI: http://eprints.soton.ac.uk/id/eprint/54755
ISSN: 0148-0227
PURE UUID: 9fbaf5f7-d0d2-4da1-99f5-10598c2d4645

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Date deposited: 18 Jul 2008
Last modified: 13 Mar 2019 20:38

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Contributors

Author: L.A. Amy
Author: A. Hogg
Author: J. Peakall
Author: P.T. Talling

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