The interpretation of the extent of late Wisconsin glaciation in southeastern Alaska has varied between geologists and biologists. Maps and reports of the region prepared by geologists commonly indicated that late Wisconsin ice extended as a large uniform front west to the edge of the continental shelf. However, the distribution of plants and animals in the region has led many biologists to suggest that there may have been ice-free areas that served as refugia during the late Wisconsin. Based on analyses of aerial photographs, topographic maps, and bathymetric charts, in conjunction with a review of previous literature and reconnaissance fieldwork throughout the region, this study presents data supporting a limited ice extent in the Alexander Archipelago during the late Wisconsin and identifies possible ice-free areas that may have served as refugia. These areas include (1) the Fairweather Ground, (2) the Herbert Graves Island area, (3) the western coast of southern Baranof Island and adjacent continental shelf, (4) Coronation Island and the adjacent continental shelf, (5) the Warren Island area, (6) the continental shelf from west of Heceta Island to Forrester Island in the south, (7) parts of the west coast of southern Dall Island, and (8) lowland areas in southern Prince of Wales Island. The identification of these possible refugia has bearing on the recolonization of the Alexander Archipelago, as they could have served as centers of biotic dispersal upon regional deglaciation and as stepping stones for early humans with a maritime tradition entering the western hemisphere from Asia.

SUMMARYTree roots, exposed by hillslope erosion in the Piceance basin of Colorado, were inspected to determine average net erosion rates during the last four centuries. Twenty pinyon pine and juniper root sections were obtained from each of five sites in this region. The date when a root was first exposed by erosion was determined, for 83 of the sections collected, by one of three methods: 1. time of initial cambium dieback; 2. interpretation of annual ring growth pattern; and 3. the earliest occurrence of reaction wood.Analysis indicated no significant difference in erosion rates between the five study sites. However, a strong difference in erosion rates was noted between north-facing (0.56 mm/yr) and south-facing (1.18 mm/yr) slopes. No significant difference in erosion rates were found between various south-facing aspects and local steepness of slopes. Significant differences were noted between erosion rate and the length of time the root was exposed t o erosion. Rates of erosion on south-facing slopes in the pinyon-juniper community during the last four centuries are as follows:period (years ago) 0-99 100-199 200-299 300-399 erosion rate (mm/yr)

Keuhn, S.C., Froese, D.G., Carrara, P.E., Foit Jr, F.F., Pearce, N.J.G., Rotheisler, P. (2009). Major- and trace-element characterization, expanded distribution, and a new chronology for the latest Pleistocene Glacier Peak tephras in western North America. Quaternary Research, 71 (2), 201-216 Sponsorship: NSERC Discovery grant; Alberta Ingenuity New Faculty Award to Duane FroeseThe Glacier Peak tephra beds are among the most widespread and arguably some of the most important late Pleistocene chronostratigraphic markers in western North America. These beds represent a series of closely-spaced Plinian and sub-Plinian eruptions from Glacier Peak, Washington. The two most widespread beds, Glacier Peak ?G? and ?B?, are reliably distinguished by their glass major and trace element abundances. These beds are also more broadly distributed than previously considered, covering at least 550,000 and 260,000 km2, respectively. A third bed, the Irvine bed, known only from southern Alberta, is similar in its major-element composition to the Glacier Peak G bed, but it shows considerable differences in trace element concentrations. The Irvine bed is likely considerably older than the G and B tephras and probably records an additional Plinian eruption, perhaps also from Glacier Peak but from a different magma than G through B. A review of the published radiocarbon ages, new ages in this study, and consideration in a Bayesian framework suggest that the widespread G and B beds are several hundred years older than widely assumed. Our revised age is about 11,600 14C yr BP or a calibrated age (at 2 sigma) of 13,710?13,410 cal yr BP.Peer reviewe

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