STRUCTURAL AND MORPHOLOGIC ZONES OF CHANNEL-LEVEE SYSTEMS IN LABORATORY SIMULATED FLOWS

Simulated channeled flows, using polyethylene glycol wax (PEG) extruded on slopes of 10º, 20º, and 30º at effusion rates of 0.6-6.5 mL/s, form morphologies and structures strikingly similar to the 4 zones described in the 1984 Mauna Loa (ML), Hawaii, channeled a’a flow [Lipman and Banks, 1987]: stabilized channel zone, transitional channel, zone of dispersed flow, and flow toe. The stabilized channel zone in PEG flows develops soon after extrusion. This zone exhibits an uncrusted to thinly crusted channel bounded by well established levees whose widths remain fairly constant for the duration of the eruption. Similarly, the stabilized channel zone for Flow 1 in the 1984 ML eruption formed over only 2 days and exhibited a constant geometry near the vent with the dominant movement of lava occurring within a central channel bounded by levees. A mobile solid PEG crust covers most of the distinct channel in the transition zone. Here, levee widths fluctuate by accretion of new material or destruction by shear forces, as well as slow lateral movement. The transition zone in the 1984 ML flow was also characterized by a well defined channel, and likewise the levee margins were partially mobile and modified by shear stresses. The zone of dispersed flow in laboratory simulations is characterized by marked breakdown in the levee system, resulting in an indistinct channel and the absence of discernable levees. Solid PEG crust piles up, increasing flow thickness, which is typically greater in this zone than elsewhere in the flow. In the zone of dispersed flow on the 1984 ML flow, a defined channel was absent as lava advanced across the entire flow width with slower movement occurring at the margins; these characteristics are also observed in PEG flows. Liquid wax advancing at the front margin of the zone of dispersed flow is classified as the flow toe. Quantitative analysis of channeled flow morphologies in the laboratory reveal important information to the evolution these flow systems that can be applied to subaerial, submarine, or extraterrestrial lava flows.