Radiative temperature measurements at Kupaianaha Lava Lake, Kilauea Volcano, Hawaii

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Abstract
Field spectroradiometer data in the wavelength range of 0.4–2.5 μm and spectral resolution of 1–5 nm have been used to compute the radiative temperature of the surface of Kupaianaha lava lake, Kilauea Volcano, Hawaii. Two sets of observations (a total of 120 spectra) were made on October 12, 1987, and January 23, 1988, when the lava lake was in a period of active overturning. The area of the surface for which temperatures were measured was ∼0.23–0.55 m2. Two numerical models of two and three components have been used to match the measured radiant flux ratios and to describe the surface of the lava pond in terms of radiant area and temperature. Three stages of activity on the lake surface are identified: Stage 1, characterized by magma fountaining and overturning events exhibited the hottest crustal temperatures (180–572°C) and the largest fractional hot areas (> 10−3). Stage 1 average flux densities were ∼2.2 × 104 W/m2, the highest recorded for the three stages of activity on either day. The largest radiative area of fresh magma was 29% at 1100°C, while cooling from magmatic temperatures to newly formed crust at 790°C took place in a matter of seconds. Stage 2, marked by rifting events between plates of crust, exhibited crustal temperatures between 100 and 340°C with fractional hot areas at least an order of magnitude lower than those found for stage 1. Average flux densities calculated for three examples of stage 2 activity were 5.3 × 103 W/m2. Stage 3, which was quiescent periods when the lake was covered by a thick crust, dominated the activity of the lake both temporally and spatially over 90% of the time. The characteristic crustal temperature of stage 3 was 80–345°C with most solutions near 200–300°C and fractional hot areas of ≤ 10−5 of the viewing area. Average flux densities for stage 3 were 4.9 × 103 W/m2. For many stage 3 examples, a two‐component model was sufficient to describe the spectral data; however, for almost all of the stage 1 and 2 examples and the remainder of the stage 3 examples a three‐component model was required. These determinations of lava temperature and radiant area have relevance for satellite and airborne measurements of the thermal characteristics of active volcanoes and indicate that temporal variability of the thermal output of lava lakes occurs on the time scale of seconds to minutes.