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.