When a volcanic eruption occurs in a populated area, timely and accurate predictions of lava flows can save lives and reduce infrastructure and property losses. To ensure that current lava prediction models can provide outputs fast enough to be useful in practice, they unfortunately must incorporate physical simplifications that limit their accuracy.
To aid evacuation plans, forecast models should predict the speed, direction, and extent of a lava flow. These attributes are intimately related to the way lava solidifies as it cools. Yet, to achieve real-time velocity, most current models assume that a flow has a uniform temperature. This is a major simplification that directly influences the modeled cooling rates; generally, lava flows are much cooler at their boundaries, where they are in contact with the air or the ground, than they are inside.
In an effort to strike a better balance between speed and realism, David Hyman and a team developed a physics-based 2D lava flow model called Lava2d. They extended the traditional vertically averaged treatment of a lava packet by viewing it as three distinct regions: the portion near the lava-air boundary, the portion near the lava-soil boundary, and the central fluid core. The upper and lower regions of a modeled flow cool according to the physics of heat transfer to the air and ground, while the temperature in the center remains uniform, as in previous approaches. This configuration allows the model to take into account a temperature gradient without requiring a computationally expensive 3D approach.
To evaluate the technique, the authors applied Lava2d to three increasingly realistic scenarios: a hypothetical synthetic flow, a laboratory-created flow described in the literature, and a flow from an actual eruption. They found good agreement between the extent and velocity of the flow modeled and measured for the laboratory flow, although the modeled surface temperatures of the flow were colder than those measured, a discrepancy which the authors attribute to the difficulty of modeling the experimental setup.
For the real-world test, the researchers configured the model with inputs based on the first hours of Mauna Loa’s 1984 eruption. They then simulated 12 hours of flow, comparing the modeled extent to the measured positions of the real flow at the end of the eruption. The model correctly identified the general morphology of the actual stream, although the extents of various substreams were underestimated or overestimated.
The computational efficiency of the model, however, was clear. The 12 hours of simulated flow was achieved in just 4.5 minutes of computation time. In a real-world forecasting scenario, this speed would allow an ensemble of model runs to be run and averaged, the researchers note, which would help compensate for inaccuracies in individual runs. Their research is published in the Journal of Geophysical Research: Solid Earth.
Image: Italian Stromboli erupts
David M. R. Hyman et al, Towards next-generation lava flow prediction: development of a rapid, physics-based lava propagation model, Journal of Geophysical Research: Solid Earth (2022). DOI: 10.1029/2022JB024998
Provided by American Geophysical Union
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