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The influence of slope breaks on lava flow surface disruption
Author(s) -
Glaze Lori S.,
Baloga Stephen M.,
Fagents Sarah A.,
Wright Robert
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2013jb010696
Subject(s) - lava , mechanics , eddy , dissipation , vortex , radius , flow (mathematics) , turbulence , geology , geophysics , physics , volcano , thermodynamics , seismology , computer security , computer science
Changes in the underlying slope of a lava flow impart a significant fraction of rotational energy beyond the slope break. The eddies, circulation, and vortices caused by this rotational energy can disrupt the flow surface, having a significant impact on heat loss and thus the distance the flow can travel. A basic mechanics model is used to compute the rotational energy caused by a slope change. The gain in rotational energy is deposited into an eddy of radius R whose energy is dissipated as it travels downstream. A model of eddy friction with the ambient lava is used to compute the time‐rate of energy dissipation. The key parameter of the dissipation rate is shown to be ρR 2 / μ , where ρ is the lava density and μ is the viscosity, which can vary by orders of magnitude for different flows. The potential spatial disruption of the lava flow surface is investigated by introducing steady state models for the main flow beyond the steepening slope break. One model applies to slow‐moving flows with both gravity and pressure as the driving forces. The other model applies to fast‐moving, low‐viscosity, turbulent flows. These models provide the flow velocity that establishes the downstream transport distance of disrupting eddies before they dissipate. The potential influence of slope breaks is discussed in connection with field studies of lava flows from the 1801 Hualalai and 1823 Keaiwa Kilauea, Hawaii, and 2004 Etna eruptions.