Thermal infrared spectral character of Hawaiian basaltic glasses

Multispectral thermal infrared remote sensing of Hawaiian basalts younger than a few hundred years old can be used to discriminate basalt lava flows that are difficult to map with visible and near-infrared images. Laboratory thermal infrared reflectance spectra of the exposed surfaces of Mauna Loa and Kilauea basalts show systematic changes with age. Fresh glass collected from active lava flows shows a broad reflectance feature between 8 and 12 μm, indicative of a strong degree of disorder. After a few weeks of exposure to the environment the spectra of the top surfaces of samples begin to exhibit spectral features suggestive of ordering into silicate chainlike and sheetlike units. With progressive aging, features of apparent sheetlike structures become the preferred mode. As soon as 3 years after emplacement, a silica-rich coating can begin to develop on the surfaces, adding another spectral feature to the laboratory reflectance measurements. The Thermal Infrared Multispectral Scanner (TIMS) with six channels between 8 and 12 μm has been used to take advantage of these spectral differences in basalts to map flows in Hawaii. Remote sensing instruments with increased spectral resolution in the thermal infrared would aid in further discrimination of basalts with more subtle differences in age, quenching, and weathering histories.