RADIATIVE TEMPERATURE-MEASUREMENTS AT KUPAIANAHA LAVA LAKE, KILAUEA VOLCANO, HAWAII

Field spectroradiometer data in the wavelength range of 0.4-2.5 mum an d spectral resolution Of 1-5 nm have been used to compute the radiativ e temperature of the surface of Kupaianaha lava lake, Kilauea Volcano, Hawaii. Two sets of observations (a total of 120 spectra) were made o n 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 temper atures were measured was approximately 0.23-0.55 m2. Two numerical mod els of two and three components have been used to match the measured r adiant flux ratios and to describe the surface of the lava pond in ter ms of radiant area and temperature. Three stages of activity on the la ke surface are identified: Stage 1, characterized by magma fountaining and overturning events exhibited the hottest crustal temperatures (18 0-572-degrees-C) and the largest fractional hot areas (> 10(-3)). Stag e 1 average flux densities were approximately 2.2 x 10(4) W/m2, the hi ghest recorded for the three stages of activity on either day. The lar gest radiative area of fresh magma was 29% at 1100-degrees-C, while co oling from magmatic temperatures to newly formed crust at 790-degrees- C took place in a matter of seconds. Stage 2, marked by rifting events between plates of crust, exhibited crustal temperatures between 100 a nd 340-degrees-C with fractional hot areas at least an order of magnit ude lower than those found for stage 1. Average flux densities calcula ted for three examples of stage 2 activity were 5.3 x 10(3) W/m2. Stag e 3, which was quiescent periods when the lake was covered by a thick crust, dominated the activity of the lake both temporally and spatiall y over 90% of the time. The characteristic crustal temperature of stag e 3 was 80-345-degrees-C with most solutions near 200-300-degrees-C an d fractional hot areas of less-than-or-equal-to 10(-5) of the viewing area. Average flux densities for stage 3 were 4.9 X 10(3) W/m2. For ma ny stage 3 examples, a two-component model was sufficient to describe the spectral data; however, for almost all of the stage 1 and 2 exampl es and the remainder Of the stage 3 examples a three-component model w as 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 variab ility of the thermal output of lava lakes occurs on the time scale of seconds to minutes.