Satellite thermal analysis of the 1986 Izu-Oshima lava flows

Surface temperatures of the eruption products and fumaroles associated with the 1986 eruption of Izu-Oshima volcano, Japan, were analysed using Landsat Thematic Mapper (TM) imagery acquired between about one and eight months after eruption cessation. Field observations and video footage of the eruption assisted the analysis. Throughout the post-eruptive period studied, the eruptive products showed elevated radiance in the TM thermal infrared channel (band 6; 10.4–12.5 μm), equating to pixel-integrated temperatures of 6–48 °C. The TM shortwave infrared channels (band 5; 1.55–1.75 μm and band 7; 2.08–2.35 μm) are sensitive just to higher temperature objects, and thermal signatures were found only at the fumarolic areas where temperatures estimated with the ‘dual band’ method were a maximum of 700–800 °C. In TM band 6, a systematic surface temperature difference (which decreased with time after the eruption) was observed between two clastogenic lava flows (LB I and LB III) that erupted at shortly spaced intervals on 21 November 1986 (16:20–22:00 h local time). Potential reasons for this temperature difference are explored, with the conclusion that the cause is a difference in the explosivity (which relates to fountaining height and degrees of magma fragmentation) of the two fire fountains, rather than differences in magmatic flow temperature, surface structure or any non-volcanic factor. Explosivity was greater for the fire-fountain feeding LB III than LB I, thereby causing a more extensive heat loss during the airborne passage of the LB III fragments due to their, on average, more fragmented nature and longer flight times. Thus the temperature of the hot core of the LB I flow remained higher than that of LB III, and this was reflected in the surface temperature of the upper clinker of the flow when imaged by Landsat TM.