An empirical function to estimate the depths of linear hot sources: Laboratory modeling and field measurements of lava tubes |
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| Authors: | Antony R Berthelote Anupma Prakash Jonathan Dehn |
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| Institution: | (1) University of Alaska Fairbanks Geophysical Institute, 903 Koyukuk Dr, P.O. Box 757320, Fairbanks, AK 99775-7320, USA |
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| Abstract: | Estimating depths of buried lava tubes is important for determining the thermal budgets and effusion rates of basaltic volcanic
systems. This research used a laboratory experiment scaled to a lava tube system to measure the 3D temperature field surrounding
a hot viscous fluid flowing through a buried glass tube while varying conditions such as flow rate and temperature. The depth
of the glass tube was changed for different experimental runs. Numerical techniques were applied to model the laboratory experiment.
The surface thermal distributions from 166 thermal traverses, constrained to a depth to width ratio of 0.6 to 1.6, were analyzed
to empirically derive a depth estimation function using regression techniques. This “Linear Anomaly Surface Transect (LAST)”
depth function is a scaleable depth estimation technique which can be solved with thermal imaging data alone. The minimum
temperature, maximum temperature and width of a Lorentzian distribution fit to a surface thermal transect, are the only inputs
required for the LAST function to estimate the depths of the hot source. The input parameters were then applied to non-laboratory
situations including the Kuhio lava tube system in Hawai’i. The LAST function produced depth estimates of ∼ 0.3 m for the
Kuhio lava tube in Hawai’i, which did not agree with observations on the ground. This is the result of the complex composition
and geometry of an actual lava tube where heat transfer is controlled by more than a simple fluid filling a tube, but also
by convection of gasses and fluids in a partially filled passage. Though not effective for lava tubes at this time, the model
provides promising results for simple cases applied to engineering and underground coal fires. |
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| Keywords: | Depth Modeling Kuhio lava tube Thermal infrared Finite element modeling Remote sensing |
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