Skip Navigation | ANU Home | Search ANU | Directories
The Australian National University
Research School of Earth Sciences
Printer Friendly Version of this Document
RSES SITE SEARCH
Untitled Document

The dynamics of solidifying lava flows with a Bingham yield strength rheology

Jesse Robertson, Ross Kerr and Ross Griffiths

Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia

Overhead photograph of a slurry of polyethylene glycol and kaolin, flowing from right to left down a 8 cm wide sloping rectangular channel.  The flow is overlain by cold water, and freezes to form a central raft of smooth solidified crust, separated from the walls by two shear layers.

 

Lava flows cover much of the Earth, the Moon, Mars, Venus, and several satellites of the outer planets. They vary greatly in their viscosities and eruption rates and form a wide range of flow types from long channel and tube flows to lava domes. Recent research in the GFD Laboratory has focused on surface crust formation, channel formation and flow morphology in Newtonian fluids subject to surface cooling (Griffiths et al. 2003; Kerr et al. 2006). This work predicts the behaviour of crystal-poor lava flows with a Newtonian rheology, such as some proximal basaltic flows on Kilauea Volcano, Hawaii and submarine lava flows near submarine spreading ridges. However, many lava flows contain sufficient crystals for the lava to have a viscoplastic 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.

Experiments carried out this year have aimed to develop a quantitative understanding of solidification, cooling mechanisms, and tube formation in lava flows with a Bingham viscoplastic rheology. In these experiments, slurries of polyethylene glycol and kaolin flowed down a long sloping channel under water. We systematically varied flow rate, slope and channel width for flows with no cooling, flows with cooling but no solidification, and flows with cooling and solidification (Figure 1). This data set will allow us to determine the roles of yield strength, flow rate, cooling rate, slope and aspect ratio in governing surface crust distribution, the critical conditions for transition from open channel to lava tube flow, and the thermal efficiency of the flows.

 


Griffiths RW, Kerr RC, Cashman KV (2003) Patterns of solidification in channel flows with surface cooling. Journal of Fluid Mechanics 496: 33-62
Kerr RC, Griffiths RW, Cashman, KV (2006) The formation of channelized lava flows on a slope. Journal of Geophysical Research 111: B10206, doi:10.1029/2005JB00422