THE INFLUENCE OF LAVA CHANNEL WIDTH VARIATIONS AND CHANNEL BENDS ON THE LENGTHS, DIMENSIONS, AND MORPHOLOGIES OF LAVA FLOWS

The dimensions and morphologies of channelized lava flows are controlled by a variety of factors that are important for understanding potential volcanic hazards for communities at risk. Two such factors are changes in channel width and lateral changes in flow path direction, which can disrupt the flow surface crust and cause enhanced cooling, significantly affecting the distance the flow can travel. Thermal models are developed and applied to examples of surface crust disruption observed in images and videos of active Hawaiian lava flows from the 2018 eruption of Kīlauea Volcano. The model estimates the evolution of core temperature of a flow along its length due to changes in surface crustal coverage caused by (i) channel width variations (narrowing and widening) and (ii) channel bends. For channel narrowing and widening, conservation of volume requires a combination of changes in flow depth and velocity to accommodate the increase or decrease in channel width. A width decrease is found to result in a velocity increase, which also increases the surface shear stresses. The primary result is that the narrowing channel increases the surface area of exposed incandescent lava along the channel walls, where shear stresses are greatest. The widening channel decreases the surface area of exposed lava. For channel bends, the fraction of exposed lava is related by a constant of proportionality to the angle through which the flow turns. The results from both cases are used in the thermal models to calculate changes in core temperature with distance, showing that even small changes in lava core exposure can have significant influences on flow rheology, and ultimately the final lengths and dimensions of the flow.