Entry_ID: (required) Entry_Title: Map of glacial limits and possible refugia in the southern Alexander Archipelago, Alaska, during the late Wisconsin glaciation Group: Data_Set_Citation Originator(s): P.E. Carrara; T.A. Ager; J.F. Baichtal; D. Paco VanSistine Title: Map of glacial limits and possible refugia in the southern Alexander Archipelago, Alaska, during the late Wisconsin glaciation Publication: U.S. Geological Survey Miscellaneous Field Studies Map Publication_Date: 2003 Publication_Place: Denver, Colorado Publisher: U.S. Geological Survey Edition: version 1.0 Data_Presentation_Form: map URL: http://pubs.usgs.gov/mf/2003/mf-2424/ End_Group Keyword: Glacial limits Keyword: Bathymetry Keyword: Cordilleran ice sheet Group: Temporal_Coverage Start_date: 2003 Stop_date: 2003 End_Group Data_Set_Progress: complete Group: Spatial_Coverage Southernmost_Latitude: 54.21530596 Northernmost_Latitude: 57.29756559 Westernmost_Longitude: -136.27626612 Easternmost_Longitude: -131.1200724 End_Group Location: United States of America Location: Alaska Location: Southern Alexander Archipelago Group: Data_Resolution Latitude_Resolution: 112.65703125 Longitude_Resolution: 112.65703125 End_Group Access_Constraints: none Use_Constraints: none. Acknowledgment of the U.S. Geological Survey would be appreciated in products derived from these data. Originating_Center: (required) Group: Data_Center Data_Center_Name: U.S. Geological Survey Dataset_ID: USGS Miscellaneous Field Studies Map MF-2424 Group: Data_Center_Contact Last_name: U.S. Geological Survey First_name: N/A Phone: 303-236-5486 Group: Address Central Publications Group MS-902, Box 25046 Denver Federal Center Lakewood, CO 80225-0046 USA End_Group End_Group End_Group Storage_Medium: Windows_NT, 5.0, Intel ARC/INFO version 8.2 Group: Distribution Distribution_Media: online Distribution_Format : Shapefile Distribution_Size: 37 megabytes Fees: none End_Group Group: Distribution Distribution_Media: online Distribution_Format : ArcInfo export Distribution_Size: 37 megabytes Fees: none End_Group Group: Multimedia_Sample URL: http://pubs.usgs.gov/mf/2003/mf-2424/MF-2424_250_pixel_wide.gif Format: GIF Caption: Reduced-size image of the entire map sheet, 250x157 pixels, 13k bytes. End_Group Group: Multimedia_Sample URL: http://pubs.usgs.gov/mf/2003/mf-2424/mf-2424.pdf Format: PDF Caption: Printable representation of map layout, 27.5 megabytes End_Group Group: Reference End_Group Group: Summary This map, which shows bathymetric contours within the southern part of the Alexander Archipelago, Alaska, has been prepared to show the limits of the Cordilleran ice sheet in this region. Previous bathymetric data for this region showed only individual water depth data (NOAA nautical charts). By producing a bathymetric contour map of this region large geomorphic features are apparent and provide information regarding the glacial history of the region. For instance, large, deep glacial troughs, such as the Chatham Strait trough, indicate that the glacier that occupied this trough flowed to the edge of the continental shelf. Previous studies suggested that during the late Wisconsin glaciation Cordilleran ice overwhelmed the Alexander Archipelago and terminated in one vast ice front at the edge of the continental shelf. Our interpretation, based on the bathymetric contours, indicates that ice reached the continental shelf at only several locations, Chatham Strait and Dixon Entrance, while large areas of the exposed continental shelf and parts of the outer islands may have been ice free. During the late Wisconsin glaciation (circa 26,000-13,000 carbon-14 yr BP) the Cordilleran glacier complex formed vast ice fields and large glaciers along the crest of the Coast Mountains. As these glaciers flowed west to the Pacific Ocean, they were joined by local glaciers originating on the higher reaches of the Alexander Archipelago (Mann and Hamiltion, 1995). This extensive volume of ice was channeled into deep troughs (present-day fiords) that formed major outlet glaciers, such as the glaciers that occupied Chatham Strait and Dixon Entrance. In several places along the coast, deep glacially scoured submarine troughs indicate that glaciers reached to the edge of the continental shelf. For instance, the glacier that extended into the Dixon Entrance trough is known to have extended to the edge of the continental shelf. Its retreat began sometime after 16,000-15,000 carbon-14 yr BP (Barrie and Conway, 1999). The exact extent of late Wisconsin cordilleran ice in southeastern Alaska is poorly known. Small-scale maps and reports of the region commonly show or imply ice extending west to the edge of the continental shelf (Capps, 1931; Coulter and others, 1965; Flint, 1971; Pewe, 1975; Denton and Hughes, 1981; and Prest, 1984). These maps relied heavily on earlier work, much of it of a reconnaissance nature. The map shows our interpretation of the limit of the Cordilleran ice sheet, which is more restricted than previous estimates, and possible refugium (an area that escaped the extensive glaciation of the late Wisconsin and so provided a suitable habitat for relict species) in the southern Alexander Archipelago during the late Wisconsin glaciation. In addition to the analysis of the bathymetric map, the limits of the Cordilleran ice sheet and possible refugia were also identified by analyses of aerial photographs, USGS topographic maps (1:63,360 and 1:250,000 scales), NOAA bathymetric charts (1:20,000 and 1:40,000 scales), previous literature, and reconnaissance fieldwork throughout the region. Ice-free areas that may have served as refugia include (1) high mountain nunataks (too small to show at map scale), (2) unglaciated ocean-facing slopes and forelands (Dahl, 1946), (3) the outer islands of the Alexander Archipelago (Worley, 1980), and (4) parts of the inner continental shelf exposed by the lowering of sea level during the late Wisconsin by an estimated 125 m (Bard and others, 1990). Arc/Info coverages and shapefiles included in this dataset: extents(.shp)--probable Cordilleran ice extents >100m_cont(.shp)--bathymetric contours below -300 meters >25m_cont(.shp)--bathymetric contours above -300 meters Map political location: Southern Alexander Archipelago, Alaska Compilation scale: 1:500,000 Geology mapped in 2001-2003 End_Group Group: DIF_Author Last_name: VanSistine First_name: Paco Email: dsistine@usgs.gov Phone: 303-236-5452 Group: Address USGS, Denver Federal Center, MS-980, Box 25046 Denver, CO 80225-0046 USA End_Group End_Group DIF_Revision_Date: 2003 Science_Review_Date: