The Pavant Butte tuff cone in Millard County, Utah was erupted into the waters of glacial Lake Bonneville. The basaltic tephras that compose Pavant Butte are in various states of alteration; from nearly pristine to fully palagonitized. Their level of alteration is detectable by visible and near infrared reflectance spectrometry. Unaltered sideromelane has a very low reflectance and is characterized by Fe2+ crystal-field bands near 1 and 2 &mgr;m. With hydration the reflectance of the tephra increases; water and hydroxyl absorption bands at 1.4 and 1.9 &mgr;m also become prominent. The most highly altered tephras are palagonite tuffs which are characterized by a relatively high reflectance, deep H2O and OH absorptions, and a steep Fe3+ absorption edge in the visible. Such altered basaltic tephras may also be good models for altered soils and dust on Mars, for which remote sensing is the primary source of data. The geologic origin of these near ubiquitous martian surface materials is still undetermined; hydrovolcanism is one possible source. The palagonite tuff deposits at Pavant Butte were remotely observed by two airborne imaging spectrometers, and the data used for compositional mapping.

The palagonite tuff was used as an endmember in a linear spectral mixing model analysis. This method was also used to calibrate the remotely sensed data to reflectance. Reflectance spectra from the airborne systems validated the laboratory sample spectra and indicated the presence of both di- and trioctahedral clay minerals within the palagonite tuff.