OKConeA5km_polyline approximate hazard zone for ballistics from Cone A OKContinuousGPS_point location of continuous GPS stations OKCraterCrFlood_polyline approximate limits of Crater Creek Flood hazard zone OKCreeks_polyline major creeks around Okmok Volcano OKDebrisArrows_polyline arrows showing the approximate location and direction of flow of debris avalanches that could occur on the steep flanks of Tulik Volcano and the inner caldera walls of Okmok Volcano OKDebrisTDA_polyline mapped boundary of a prehistoric debris avalanche from Tulik Volcano OKDebrisTulik_region approximate hazard zone for debris avalanches with source areas on the steep flanks of Tulik Volcano OKFlood_region approximate location of flood and lahar hazards OKFtGlennAir_point location of the Fort Glenn airstrip OKHazMapBdry_polyline outline of the basemap OKLatLines_polyline four 10-minute latitude lines in the map area OKLongLines_polyline four 20-minute longitude lines in the map area OKPFsurge_polyline approximate location of pyroclastic flow and surge hazard zone OKRim15km_polyline approximate limit of significant ashfall, located 15 kilometers from the caldera rim OKRim30km_polyline approximate maximum extent of pyroclastic flows, sures, and lateral blasts during a very large eruption, located 30 kilometers from the caldera rim OKroad_polyline unmaintained dirt roads OKSeisStat_point location of seismic stations OKtrail_polyline unmaintained trails
Beget, J.E., Larsen, J.F., Neal, C.A., Nye, C.J., and Schaefer, J.R., 2005, Preliminary volcano-hazard assessment for Okmok Volcano, Umnak Island, Alaska: Report of Investigation RI 2004-3, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, AK.Online Links:
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 0.01
Ordinates (y-coordinates) are specified to the nearest 0.01
Planar coordinates are specified in meters
The horizontal datum used is WGS 1984.
The ellipsoid used is WGS 1984.
The semi-major axis of the ellipsoid used is 6378137.0000.
The flattening of the ellipsoid used is 1/298.257224.
List of station names
longitude value
latitude value
elevation value
Not all line objects have creek names. Major creeks are named, others are unnamed.
values of latitude
values of longitude
List of station names
longitude value
latitude value
This dataset was compiled by the authors with funds from the Alaska Volcano Observatory, a joint program of the U.S. Geological Survey, the University of Alaska Fairbanks-Geophysical Institute, and the Alaska Division of Geological & Geophysical Surveys.
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This dataset was created to illustrate, at a scale of 1:150,000 the approximate location of volcanic hazard zones around Okmok Volcano.
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Attributes in this dataset consist of GPS and seismic station names and locations, latitude and longitude line labels, and creek names. The accuracy was checked by plotting the attributes as labels in a GIS, then checking the label against the source information. Seismic and GPS station locations and names were checked using the original source data. The latitude and longitude line labels were checked by displaying them in GIS and comparing the attribute value to the actual location. The creek labels were plotted then compared to the USGS 1:250,000-scale topographic map of Umnak Island. Creek names were also derived and visually checked from Byers, F.M., 1959, Geology of Umnak and Bogoslof Islands, Aleutian Islands, Alaska: U.S. Geological Survey Bulletin 1028-L, p. 167-369.
The accuracy of the estimated extent of any of the volcanic hazard zones should not be confused with the horizontal accuracy of the GIS data file. For example, the 5 kilometer circle drawn around cone A for ballistics hazards is positionally accurate to about 550 meters, based on the estimated "center" of cone A, however, ballistics could possibly travel much shorter or much longer distances, depending on the eruption magnitude (see text for details of each eruption hazard, DGGS RI2004-3). Most data layers were digitized on the shaded relief image OKhazbase.tiff, which has a horizontal accuracy of 60 meters (see metadata file RI2004-3_basemap_meta.txt) Each GIS layer is listed below with a brief description of its horizontal accuracy. OkmokConeA5km_polyline A 5 km circle was generated around the center point of Cone A. The center of cone A was approximated visually from the georeferenced shaded relief basemap image (OKhazbase.tiff). Accuracy is approximately 550 meters, which is the vent diameter. Cone A center (x,y)deg = (-168.2415, 53.3992); (x,y)meters = (683,393E, 5,920,230N). OKContinuousGPS_point Continuous GPS station locations are accurate to approximately 1 centimeter. OKCraterCrFlood_polyline This approximated hazard zone was sketched from the shaded relief image basemap and is based on field evidence of drainage patterns of lahars and floods down Crater Creek over the last approximately 2,000 years. OKCreeks_polyline Creeks were originally digitized from the USGS 1:250,000-scale georeferenced DRG topographic map of Umnak Island. The creeks were reprojected in MapInfo version 6.0 from the raster topo base of UTM NAD27 to UTM WGS84 to match the projection of the shaded relief basemap (OKhazbase.tiff). After reprojection the creeks were hand-edited in GIS and required adjustments up to 150 meters to fit the shaded relief basemap (OKhazbase.tiff). OKDebrisArrows_polyline Debris arrows are randomly placed on the steep flanks of Tulik Volcano and the inner caldera wall of Okmok Volcano. OKDebrisTDA_polyline This boundary is based on field geologic mapping at a scale of 1:63,360 and photo-interpretation resulting in a horizontal accuracy of about 500 meters. OKDebrisTulik_region This generalized boundary is based in part on the extent of the prehistoric debris avalanche at Tulik Volcano (file OKDebrisTDA). OKFlood_region Flood and lahar hazard zones were sketched from drainage patterns apparent on the Landsat7 GeoTIFF L72077023_023320000817_B80 of Umnak Island, acquired on 17 August 2000. The file was converted to red band 5, green band 4, and blue band 2 to enhance drainage patterns. Drainages with headwaters on the high flanks of the volcano are portrayed. OKFortGlennAir_point Location derived from USGS 1:250,000-scale Umnak Island quadrangle DRG topographic map. Accuracy approximately 150 meters. OKHazMapBdry_polyline Outline of OKhazbase.tiff, accurate to pixel size of OKhazbase.tiff (30 meters). OKLatLines_polyline Generated in GIS from decimal degree end points to an accuracy of 5 decimal points, or approximately 1 meter. OKLongLines_polyline Generated in GIS from decimal degree end points to an accuracy of 5 decimal points, or approximately 1 meter. OKPFsurge_polyline Centered 10 kilometers around cone A (cone A center accuracy about 550 meters) with an approximate 17 kilometer extension downslope out through the breach in the caldera. OKRim15km_polyline The approximate diameter of the somewhat circular caldera is 10 kilometers, therefore a 20-kilometer circle was generated in a GIS around the approximate center of the caldera. The center of the caldera was approximated visually in a GIS from the georeferenced shaded relief basemap (OKhazbase.tiff). Accuracy is approximately 1,500 meters. For this purpose, the caldera center was positioned at (x,y)deg = (-168.4372, 53.4348); (x,y)meters = (670,243E, 5,923,700N). OKRim30km_polyline The approximate diameter of the somewhat circular caldera is 10 kilometers, therefore a 35 kilometer circle was generated in a GIS around the approximate center of the caldera. The center of the caldera was approximated visually in a GIS from the georeferenced shaded relief basemap (OKhazbase.tiff). Accuracy is approximately 1,500 meters. For this purpose, the caldera center was positioned at (x,y)deg = (-168.4372, 53.4348); (x,y)meters = (670,243E, 5,923,700N) OKroad_polyline Roads were digitized from the USGS 1:250,000-scale Umnak Island quadrangle DRG topographic map, then reprojected from UTM NAD27 to UTM WGS84 in MapInfo version 7.0. Accuracy is approximately 150 meters. OKSeisStation_point Seismic stations were located with hand-held GPS units (accuracy less than 15 meters) except OKCD, OKFG, and OKCE, which were located with differentially corrected Trimble GPS units with an accuracy of less than 1 centimeter. OKtrail_polyline Trails were digitized from the USGS 1:250,000-scale Umnak Island quadrangle DRG topographic map, then reprojected from UTM NAD27 to UTM WGS84 in MapInfo version 7.0. Accuracy is approximately 150 meters.
This dataset includes preliminary information pertaining to the volcanic hazards at Okmok Volcano, Umnak Island, Alaska.
The latitude and longitude attributes of the seismic stations and GPS station files were reformatted so that the column labels were consistent and that both sets of data are reported in decimal degrees, WGS84 datum.
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Report of Investigation 2004-3
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