Cooling rate of an active Hawaiian lava flow from nighttime spectroradiometer measurements

A narrow‐band spectroradiometer has been used to make nighttime measurements of the Phase 50 eruption of Pu'u O'o, on the East Rift Zone of Kilauea Volcano, Hawaii. On February 19, 1992, a GER spectroradiometer was used to determine the cooling rate of an active lava flow. This instrument collects 12‐bit data between 0.35 to 3.0 μm at a spectral resolution of 1 – 5 nm. Thirteen spectra of a single area on a pahoehoe flow field were collected over a 59 minute period (21:27 – 22:26 HST) from which the cooling of the lava surface has been investigated. A two‐component thermal mixing model [Flynn, 1992] applied to data for the flow immediately on emplacement gave a best‐fit crustal temperature of 768°C, a hot component at 1150°C, and a hot radiating area of 3.6% of the total area. Over a 52‐minute period (within the time interval between flow resurfacings) the lava flow crust cooled by 358°C to 410°C at a rate that was as high as 15°C min −1 . Our observations have significance both for satellite observations of active volcanoes and for numerical models of the cooling of lava flows during their emplacement.