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Colluvium on foot slopes in parts of North America and Europe has been attributed to a major mass-wasting episode during the last glacial period. Stratigraphic evidence and 14C ages support this hypothesis for the northern part of the Upper Mississippi Valley. Colluvium in this region grades laterally into, or interfingers with, fluvial sediment beneath the late Wisconsinan Savanna terrace. Colluvial foot slopes are truncated by fluvial surfaces postdating the incision that created the Savanna terrace between 13 and 11 ka. Samples from within the colluvium have Inc ages between 18.6 and 12 ka. Ages of 28.9 and 20.3 ka have been obtained from beneath colluvium, and fluvial sediment inset into colluvial foot slopes has yielded ages between 12.5 and 9.8 ka. Widespread permafrost during the late Wisconsinan glacial maximum may explain the onset of accelerated mass wasting that produced the colluvium, although mass wasting apparently continued for some time during subsequent climatic warming. The results described here imply major, long-term, climatically driven fluctuations in sediment supply from hillslopes to the fluvial system in this region.

The magnitude of flooding can be affected by small changes in climate, as shown by the past 7,000 years of the Upper Mississippi River tributaries. Analysis of the geological record shows that larger floods occurred as climate cooled, such as at times preceding the Little Ice Age. Flood sizes increased from standard 50-year floods to 500-year floods or greater, while temperature only changed one to two degrees centigrade on average and rainfall increased from 10% to 20% annually.

Fixed-bed adsorption is widely used in industrial gas separation and is the primary method for atmosphere revitalization in space. This paper analyzes the uncertainty of a one-dimensional, fixed-bed adsorption model due to uncertainty in several model inputs, namely, the linear-driving-force (LDF) mass transfer coefficient, axial dispersion, heat transfer coefficients, and adsorbent properties. The input parameter uncertainties are determined from a comprehensive survey of experimental data in the literature. The model is first calibrated against experimental data from intra-bed centerline concentration measurements to find the LDF coefficient. We then use this LDF coefficient to extract axial dispersion coefficients from mixed, downstream concentration measurements for both a small-diameter bed (dominated by wall-channeling) and a large-diameter bed (dominated by pellet-driven dispersion). The predicted effluent concentration and temperature profiles are most strongly affected by uncertainty in LDF coefficient, adsorbent density, and void fraction. The uncertainty analysis further reveals that ignoring the effect of wall-channeling on apparent axial dispersion can cause significant error in the predicted breakthrough times of small-diameter beds. [ABSTRACT FROM AUTHOR]