Discrimination of Hydrovolcanic Tephras from Volcanic and Non-volcanic Backgrounds in Hyperspectral Data of Pavant Butte and Tabernacle

Introduction: Water-magma, or ice-magma, interactions have long been theorized as an important process in the Martian geologic record [1-3]. The ability to unambiguously recognize tephra deposits and volcanic edifices produced by H 2 O-magma interactions is important for understanding the geologic history of Mars and for understanding the genesis of the major components of the Martian surface layer. Recognizing volcanic edifices produced by H 2 O-magma interactions on the basis of morphology alone is difficult. Analysis of Viking imagery led to the tentative identification of numerous tuyas, moberg hills and ridges [1]. Likewise, rootless cones have been identified in MOC Narrow Angle camera imagery [4,5]. However, the identification of tuyas, moberg hills and tuff cones is not definitive and supporting evidence will be requird before these features can be definitively identified as such. One means of providing supporting evidence for the identification of hydrovolcanic landforms and tephra deposits is through spectroscopy. Tephras produced by hydrovolcanic activity range from fresh basaltic glass (sideromelane) to glasses that have been completely altered to palagonite. A study of the visible through shortwave infrared (Vis-IR) reflec-tance of tephras composing tuff rings and tuff cones showed that the different stages of this alteration sequence have recognizable reflectance signatures [6,7]. However, the ability to recognize these different types of tephras against volcanic and non-volcanic background materials has yet to be fully demonstrated. In this research, hyperspectral Vis-IR data over volcanic and hydrovolcanic terrains in the Black Rock Desert of Utah were analyzed in order to determine the separability of the component materials from volcanic and non-volcanic backgrounds. Study Area. Pavant Butte is a tuff cone erupted into Pleistocene Lake Bonneville in west-central Utah approximately 15,600 years ago [8]. It consists of a highly palagonitized tuff cone which lies atop fresh to poorly palagonitized ash beds. South of Pavant Butte lies the younger moderately palagoni-tized Tabernacle Hill tuff ring and between them lies a more recent basalt flow. Laboratory reflectance spectra of the principal hydrovolcanic tephras are presented in Figure 1. The reflectance of the Tabernacle hill tuffs is approximately the same as that of the gray, moderately palagonitized tuff shown in