Implications of using broadband photometry for compositional remote sensing of icy objects

Water ice has such a low absorption coefficient at visual wavelengths (～0.01 cm^?1) that a very small amount of particulate material can significantly darken an icy surface. A variety of ice plus particle mixtures were studied to show that particulate contaminations of ～1% by weight (even 0.1% or less in some cases) in ice or frosts result in reflectance levels close to that of the contaminants. In a very clear ice (no bubbles) it is plausible to have a reflectance < 0.05 for particulate contaminations ～10^?7 by weight for submicron dark particles, such as carbon lampblack. Scattering conditions compete for domination with contaminants for control of visual reflectance, implying that the apparent reflectivity level and color of a surface is a poor indicator of ice content. A dark surface (e.g., albedo 0.05) does not necessarily imply that there us very little water ice present. Infrared JHK colors of water ice and other minerals, including ice-mineral mixtures, show that some orthopyroxenes can have JHK colors very similar to fine-grained water frosts. In general, it is possible that the JHK colors of an ice plus particulate mixture can fall anywhere in the classical J-H versus H-K diagram, thus the diagram cannot be used to distinguish a predominately “rock” surface from one which is predominantely ice for one specific case. An important exception is the case where both the J-H and H-K colors are ??0.2. It appears that such colors indicate a relatively pure icy surface. In some cases, the diagram might be used as a statistical tool to distinguish between the compositions of surfaces within a class of objects, but the validity of such comparisons decreases for different classes, such as the main-belt asteroids when compared to outer solar system satellites, where water ice is more stable.     

TERRESTRIAL HEAT FLOW IN THE SWISS ALPS

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Terrestrial heat flow has been measured in three Alpine railroad tunnels. The geothermal gradients were calculated from temperatures measured during the construction of the tunnels, and corrections for topographic irregularities were made. The thermal conductivity of 113 rock specimens from the vicinity of the tunnels was measured. The heat flow in the Gotthard tunnel was found to be 1.6 10^-6 cal/cm² sec, in the Simplon 2.2 10^-6 cal/cm² sec, and in the Loetschberg 1.9 10^-6 cal/cm² sec. Most of the flux at the surface can be attributed to radioactive decay in a thickened crust, but a non-uniform distribution of radioactive elements may be required to explain the relatively high heat flow in the Simplon and Loetschberg tunnels.     

Holocene landscape evolution and the development of models for human interaction with the environment: An example from the mississippi headwaters region

Integration of a record of Holocene landscape evolution with the cultural record from a multicomponent archaeological site in northern Minnesota has fostered the development of a regional model of human interaction with the changing physical environment. Excavation of 21-CA-169 near Nushka Lake revealed two components, an aceramic Archaic zone where processing of large mammals was the major activity and an upper zone with artifacts suggestive of wild rice processing. Seasonal occupation of the lower zone occurred during a period of falling regional lake levels resulting from natural stream network evolution. The upper zone represents human occupation in a physical and biological setting that was quite different than during earlier occupation. Integration of the geomorphic history of the region along with an interpretation of the types of cultural activities occurring on the changing landscape have provided a model to understand land use and to predict the location of other sites. © 1993 John Wiley & Sons, Inc.     

Cave bears and paleolithic artifacts in Yarimburgaz Cave,Turkey: Dissecting a palimpsest

This article addresses the taphonomic issues surrounding artifact-bear associations in Yarimburgaz Cave, northwestern Turkey. Our purpose is to evaluate the circumstances of bone assemblage formation in the Middle Pleistocene deposits of the cave, identifying the agencies responsible for the accumulations and the causes of bone damage before and following deposition. Pleistocene species representation, bone damage, body part representation, and mortality data indicate that cave bear remains in Yarimburgaz are unrelated to hominid use of the same site. None of the observations on the cave bear remains contradicts the expectations developed from modern wildlife accounts of modern bear behavior; these accumulations resulted from mortality normally associated with hibernation over many generations of den use. Nonursid carnivores also played roles in bone collection and/or modification. We conclude that at least three distinct biological processes contributed to the formation of the Middle Pleistocene faunas: hibernating bears, bone-collecting carnivores such as wolves, and hominids in descending order of importance. The Yarimburgaz faunas represent palimpsests or overlays of many short-term depositional events, the close spatial associations of which are explained by slow or uneven sedimentation rates inside the cave. Although occupations by hominids appear to have been ephemeral in nature, hominids ultimately discarded nearly 1700 stone artifacts in Yarimburgaz Cave. The hominids did not discard many ungulate bones in the same circumstances. These observations suggest that hominid foraging efforts focused on resources other than large game while at the cave. © 1996 John Wiley & Sons, Inc.