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Lava flows cover much of the Earth, the Moon, Mars, Venus,
and several satellites of the outer planets. They produce
surface morphology, hold important clues to planetary
evolution, host major ore deposits and pose serious hazards
to both people and property. Lavas vary greatly in their
viscosities and eruption rates, and form a wide range of
flow types from long channel flows to lava domes. On the
Earth, basaltic flows transport enormous volumes of melt in
flood basalt eruptions, comprise the upper seafloor at fast
spreading mid-ocean ridges, and build up volcanic ‘hotspot’
islands such as Hawaii.
The dynamics of lava flows are characterized by a complex set
of thermal and mechanical interactions between the flow and its
environment, and also between properties of the lava and
processes such as solidification, shearing and stirring within
the flow. The evolution and final state of the lava flow will be
strongly influenced by the nature and timing of cooling and
solidification of the multiple mineral phases within the fluid,
as well as the internal rheology and the thermal structure of the
flow itself.
In recent research in the GFD Laboratory at RSES, novel
laboratory experiments and theoretical analysis have been
used to understand surface crust formation, channel
formation and flow morphology in Newtonian fluids subject to
surface cooling (Griffiths, Kerr and Cashman, 2003; Cashman,
Kerr and Griffiths, 2006; Kerr, Griffiths and Cashman,
2006). This work predicts the behavior of crystal-poor
lavas that behave as Newtonian fluids, such as some proximal
basaltic flows on Kilauea Volcano, Hawaii and submarine lava
flows on the East Pacific Rise. However, many lavas contain
sufficient crystals that the lava has a non-Newtonian
rheology with a substantial yield strength, including those
typical of distal Hawaiian channels and most Mt. Etna
flows. The yield strength can have a significant effect on
the velocity distribution in a channel flow, and hence
should have a major impact on the very complex interaction
between convection and surface solidification seen in
solidifying channel flows.
I aim to develop a quantitative understanding of
solidification, cooling mechanisms, channel formation and
tube formation in lava flows with a Bingham yield strength
rheology. My PhD experiments can be broken into two broad sets:
Surface solidification and flow morphology in channeled yield strength flows.
In these experiments, slurries of polyethylene glycol (PEG)
and kaolin flow down a long sloping channel under cold
salty water. I determine the roles of yield
strength, flow rate, cooling rate, aspect ratio, and slope
in governing surface crust distribution, the critical
conditions for transition from open channel to lava tube
flow, and the thermal efficiency of the flow. The results
will be scaled to highly crystalline lavas typical of distal
Hawaiian channels and most Mt. Etna flows, to interpret and
understand the observed flow morphologies, cooling rates and
surface crust distributions.
Self-organized, solidifying yield strength flows on a slope.
Following the above study of solidifying yield strength flows
in prescribed channels, I will tackle the more complex
problem of channel formation and evolution. For these
experiments on self-organized, solidifying flows, PEG-kaolin
slurries with different yield strengths and viscosities will
flow down a wide uniform slope at a constant flow rate and
temperature, under cold salty water. I will determine the
dependence of channel or tube width, channel aspect ratio
and rate of flow front advance on the yield strength and
viscosity of the PEG-kaolin slurries, the slope, the volume
flux and the thermal conditions. I will also determine the
conditions for channel flows to remain ‘open’ or to become
insulated tubes.
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