Dr. Neil Balmforth

Skinny currents, tremor and dambreaks:

Gravity currents occasionally develop solid skins. For example, cooling freezes the surface of lava flows to create a surface crust that can oppose the flow of the underlying fluid. We have been exploring models of such currents with a view towards understanding the wrinkling and buckling of the surface skin. As part of this, we have also looked into some solid mechanics problems of buckling sheets without a fluid.
Volcanic tremor has been suggested to arise from the interaction between the magma flowing through a sub-surface conduit, and the surrounding, deformable rock walls. We have elabourated on this mechanism, due to Bruce Julian, to explore whether it can indeed provide a plausible mechanism.
Certain sudden and hazardous floods have been hypothesized to result from the failure of moraine-dammed glacial lakes. A popular explanation of this failure is that an ice or rock fall into the lake generates a wave that overtops the dams and incises a small channel through which lake water can flow. The flow causes erosion, which deepens the channel, allowing more flow and more erosion. The resulting runaway cuts a deep incision into the dam and empties a good fraction of the lake in a matter of hours. We have built fluid models (both experimental and theoretical) of the process.

Click to enlarge
An elastic-plated gravity current
An elastic-plated gravity current
(experiment performed by Anja Slim in the CRS Lab at WHOI showing a current of corn syrip flowing beneath a wrinkled "elastic skin" of clingfilm)
Solution of a model of volcanic tremor
(shown is a space-time plot of the thickness of a periodic conduit containing flowing viscous fluid and bounded by elastic walls)
Dambreak experiment
(a rectangular tank holds a reservoir dammed by a mixture of sand and grit; a wave is generated that sets up a seiche in the reservoir which repeatedly washes over the dam, eventually cutting a channel that instigates a catastrophic incision)
Shear-induced buckling
Buckling atop a channel flow
Elastic-plated gravity currents

Instability in flow down elastic conduits and volcanic tremor
More volcanic tremor Interfacial instability

More Dambreaking
Thixotropic gravity currents

Department of Mathematics / Fluid Labs / Neil Balmforth / Research Interests