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The development of fluid instabilities and preferred pathways in lava flow interiors: Insights from analog experiments and fractal analysis

By
S.W. Anderson
S.W. Anderson
1
Department of Science, Black Hills State University, Spearfish, South Dakota 57799-9102, USA, and Planetary Science Institute, Tucson, Arizona 85719, USA
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S.M. McColley
S.M. McColley
2
Department of Science, Black Hills State University, Spearfish, South Dakota 57799-9102, USA
5
Present address: Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA.
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J.H. Fink
J.H. Fink
3
Department of Geology, Arizona State University, Tempe, Arizona 85287-1404, USA
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R.K. Hudson
R.K. Hudson
4
Department of Science, Black Hills State University, Spearfish, South Dakota 57799-9102, USA
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Published:
January 01, 2005

We examined the formation and evolution of preferred pathways in flow interiors by sequentially extruding different colors of polyethylene glycol wax (PEG) from a point source into a cold sucrose solution. The setup was videotaped from the top and side to show time-lapse views of the developing surface morphology, and from the bottom to capture the interaction of the different PEG colors in the flow interior. We conducted 18 experimental runs that clearly show the development of interior flow pathways as a function of emplacement variables, which include effusion rate, cooling rate, and time. High effusion rate combined with slow cooling produced extrusions with little or no surface crust, and flow interiors that displayed a breakdown of radial flow into smaller broad fronts as the experiment proceeded. Where crusts formed near the margins of some of these flows late in the run, narrower pathways formed beneath the solidified surface. Lower effusion rates and more rapid cooling produced completely crusted flows with a highly complex interior pathway network. Flow surface morphology was affected by interior pathway development. Broad interior pathways capable of applying stress over large areas resulted in widespread flow surface disruption and the formation of rifts and levees, whereas narrow finger-like pathways capable of applying stress over much smaller areas resulted in many local surface disruptions such as pillows. Pillows typically consisted of fluid that had been residing in the interior for some time, rather than the freshest, hottest liquid to emanate from the point source. We suggest that the development of Saffman-Taylor fluid instabilities in lava flow interiors leads to viscous fingering and the formation of preferred pathways. Fractal analysis suggests that these instabilities affect the tortuosity of both the exterior flow margins and the interior flow pathways. We also find many similarities between these analog flows and lava flows, and suggest that viscous fingering is an important mechanism in the emplacement of some lavas.

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Contents

GSA Special Papers

Kinematics and dynamics of lava flows

Michael Manga
Michael Manga
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Guido Ventura
Guido Ventura
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Geological Society of America
Volume
396
ISBN print:
9780813723969
Publication date:
January 01, 2005

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