USGS Geoscience Data Catalog
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100m_cont(.shp)--bathymetric contours below -300 meters 25m_cont(.shp)--bathymetric contours above -300 metersMap political location: Southern Alexander Archipelago, Alaska Compilation scale: 1:500,000 Geology mapped in 2001-2003
Carrara, P.E., Ager, T.A., Baichtal, J.F., and VanSistine, D. Paco, 2003, Map of glacial limits and possible refugia in the southern Alexander Archipelago, Alaska, during the late Wisconsin glaciation: U.S. Geological Survey Miscellaneous Field Studies Map MF-2424, U.S. Geological Survey, Denver, Colorado.
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 112.65703125
Ordinates (y-coordinates) are specified to the nearest 112.65703125
Planar coordinates are specified in Feet
The horizontal datum used is North American Datum of 1927.
The ellipsoid used is Clarke 1866.
The semi-major axis of the ellipsoid used is 6378206.4.
The flattening of the ellipsoid used is 1/294.98.
EXTENTS (probable Cordilleran ice extents) 100M_CONT (bathymetric contours below -300 meters) 25M_CONT (bathymetric contours above -300 meters) <EXTENTS.AAT> item explanation: DESCRIPTION--short description of line feature COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 FNODE# 4 5 B - 5 TNODE# 4 5 B - 9 LPOLY# 4 5 B - 13 RPOLY# 4 5 B - 17 LENGTH 4 12 F 3 21 EXTENTS# 4 5 B - 25 EXTENTS-ID 4 5 B - 29 DESCRIPTION 100 100 C - DESCRIPTION Chatham Strait fault Fairweather/Queen Charlotte fault probable late Wisconsin Cordilleran ice marginal position probable pre-late Wisconsin Cordilleran ice marginal position submarine slide scarp <100M_CONT.AAT> item explanation: CONTOUR--bathymetric contour interval, in meters below sea level (100-meter increments) COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 FNODE# 4 5 B - 5 TNODE# 4 5 B - 9 LPOLY# 4 5 B - 13 RPOLY# 4 5 B - 17 LENGTH 4 12 F 3 21 100M_CONT# 4 5 B - 25 100M_CONT-ID 4 5 B - 29 CONTOUR 8 14 F 0 CONTOUR values between -300 and -3100 (100-meter increments) <25M_CONT.AAT> item explanation: CONTOUR - bathymetric contour interval, in meters below sea level (25-meter increments) COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 FNODE# 4 5 B - 5 TNODE# 4 5 B - 9 LPOLY# 4 5 B - 13 RPOLY# 4 5 B - 17 LENGTH 4 12 F 3 21 25M_CONT# 4 5 B - 25 25M_CONT-ID 4 5 B - 29 CONTOUR 8 14 F 0 CONTOUR values between 0 and -275 (25-meter increments)
Scientific Fishery Systems, Inc. for providing the digital data base of depth soundings.
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.
Scientific Fishery Systems, Inc, 2000, Alaska Bathymetric Data: Scientific Fishery Systems, Inc, Anchorage, AK.
Person who carried out this activity:
Data were checked by the geologist who made
the observations. To check attribute accuracy, a color check plot was
visually compared to the geologist's original compilation.
Discrepancies between the digital geospatial dataset and the original
analog compilation were corrected as needed. This map has been
thoroughly reviewed for conformity with U.S. Geological Survey
editorial standards and stratigraphic nomenclature.
Many points were determined originally by GPS and(or) Loran System.
All data used from published and unpublished digital sources are
limited by the accuracy of that data. All glacial extents were on-
screen digitized from hand-drafted scanned versions drawn on
bathymetric map at 1:500,000 scale.
Data are complete: no features were eliminated or
generalized at the scale of map compilation.
Map elements were visually checked by the author for overshoots,
undershoots, duplicate features, polygon attributes, and other errors.
Automated (ARC/INFO) routines were also used to check the databases for
polygon label errors, line or point attribution errors, sliver
polygons, dangling arcs, intersection errors, and projection
information. The map was reviewed by other geologists for consistency
with basic geologic principles and general conformity to USGS mapping
Are there legal restrictions on access or use of the data?
- Access_Constraints: none
- none. Acknowledgment of the U.S. Geological Survey would be appreciated in products derived from these data.
USGS Miscellaneous Field Studies Map MF-2424
Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data.
The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials.
|Data format:||Bathymetric contours and limits of the Cordilleran ice sheet in format Shapefile (version 1.0) Size: 37 megabytes|
|Data format:||Bathymetric contours and limits of the Cordilleran ice sheet in format ArcInfo export (version 8.2) Size: 37 megabytes|