Thermal infrared spectra from both laboratory and remote sensing instruments were used to distinguish different age lava flows with varying amounts of surficial modification at Cima and Lunar Crater volcanic fields. The modification processes affecting the lava flows cause spectral differences that can be seen in remotely sensed emittance spectra from the thermal infrared multispectral scanner. Important influences on the thermal infrared spectra include aeolian mantling, vegetation, lava flow, roughness, and rock varnish. Laboratory thermal infrared reflectance spectra of the subaerially exposed surfaces of 1--15 cm basalt fragments at Cima volcanic field show a feature attributable to rock varnish on the younger flows (0.14--0.75 m.y.), that is lacking on the older flows (≥0.8 m.y.). This suggests that rock varnish is thinner on the older flows at Cima volcanic field. Scanning electron microscope images and thin sections of the different age flows at Cima volcanic field support the conclusion that rock varnish is thinner and may be eroding on the older flow surfaces. ¿ American Geophysical Union 1992