map_files: Geodatabase and ArcMap document file used to generate the April 18, 2009, topographic map of Kasatochi Island. Attribute fields in the geodatabase feature classes are generally named and organized according to the NCGMP09 - Draft Standard Format for Digital Publication of Geologic Maps, Version 1.1 by the USGS National Cooperative Geologic Mapping Program (NCGMP). map_image: GeoTIFF export of the April 18, 2009, topographic map of Kasatochi Island. elevation_data: Digital elevation models (DEM) of Kasatochi Island derived from stereoscopic satellite images acquired on April 18, 2009. Files include: 1) the originating DEM, which is based on the WGS84 ellipsoid, and an adjusted version which uses Kasatochi Mean Sea Level (KMSL) as a vertical datum.
Nye, Chris, 2017, Kasatochi Island 2009 topography: Miscellaneous Publication MP 163, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.Online Links:
This is a point data set.
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest .00000001
Ordinates (y-coordinates) are specified to the nearest .00000001
Planar coordinates are specified in Meters
The horizontal datum used is World Geodetic System of 1984.
The ellipsoid used is WGS 84.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257223563000025.
The Kasatochi Mean Sea Level vertical datum was established with the assistance of Nicole Kinsman. Cartographic guidance provided by Patricia Gallagher. Satellite data credit: the DEM was derived from an orthorectified stereoscopic pair of April 18, 2009 WorldView-1 images; the 2004 shoreline was digitized from an orthorectified April 9, 2004 QuickBird-2 image; the 2012 shoreline was digitized from an orthorectified February 2, 2012 WorldView-2 image, and gullies were digitized from April 18, 2009 WorldView-1 images. Geographic place names are all informal, and are from, or derived from, place names customarily used by US Fish and Wildlife researchers, who are the primary visitors to the island.
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The purpose of this data release is to provide updated topographic data for Kasatochi Island subsequent to the August 6-8, 2008 explosive eruption of Kasatochi volcano. The eruption increased the area of the island by about 40 %; the crater by about 30 %; and the crater lake by nearly 70 % (Scott and others, 2010). The area of the island was increased by deposition of pyroclastic deposits which extended the preexisting shoreline seaward by up to four hundred meters. The area enclosed by the crater rim was increased primarily by explosive removal of preexisting rock and redeposition of that material in pyroclastic deposits on the flanks of the volcano. In addition, the entire island was blanketed by pyroclastic deposits, which are generally not thick enough to obscure pre-existing topography, but locally reach thicknesses of up to fifty meters (Nye and others, 2017). The eruption made all existing topographic data and maps obsolete. This report provides updated topography based on a stereo pair of satellite images acquired eight months after the eruption. There has been erosional modification of the island since these data were acquired. The western, northern, and eastern shores were progressively eroded (Nye and others 2017) and now consist either of pre-existing lava outcrops or boulder beaches back by near-vertical bluffs up to 25 m high cut into 2008 pyroclastic deposits. Between 2009 and 2012 the southernmost beach was extended seaward. An extensive system of gullies formed in the 2008 eruption deposits immediately after the eruption; these gullies have deepened and widened in subsequent years, but lateral shifts have been minimal. Post-2009 elevation data necessary for updating this map has not been acquired. Pertinent references: Scott, W.E., Nye, C.J., Waythomas, C.F., and Neal, C.A., 2010, August 2008 eruption of Kasatochi Volcano, Aleutian Islands, Alaska-Resetting an island landscape: Arctic, Antarctic, and Alpine Research, v. 42, no. 3, p. 250-259, <http://doi.org/10.1657/1938-4246-42.3.250> and Nye, C.J., Scott, W.E., Neill, O.K., Waythomas, C.F., Cameron, C.E., and Calvert, A.T., 2017, Geology of Kasatochi volcano, Aleutian Islands, Alaska: Alaska Division of Geological & Geophysical Surveys Professional Report 123, <http://doi.org/10.14509/29718>
Nye, C.J., Scott, W.E., Neill, O.K., Waythomas, C.F., Cameron, C.E., and Calvert, A.T., 2017, Geology of Kasatochi volcano, Aleutian Islands, Alaska: Professional Report PR 123, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.Online Links:
Certainty in attribute interpretation may vary throughout the map. Attribute fields within each geodatabase feature class record the author's degree of confidence in the existence or identity of applicable features. The information has been examined by several geologists familiar with the study area, but the data and accompanying report have not been formally reviewed for technical content or for conformity to the editorial standards of DGGS.
Locations of several features easily identifiable on the satellite images, such as shorelines, the crater rim, gully intersections, and distinctive outcrops were measured during the course of the study with hand-held GPS units. Features on gentle terrain were found to be displayed on the images within the resolution of the hand held GPS, and the topographic data match the images to within a meter or less. From this we conclude that horizontal precision in areas of gentle terrain is generally within 1 meter. In areas of steep or near-vertical terrain the topographic data diverge from the satellite images by up to tens of meters, but we are unable to independently determine if these differences are due to lack of accuracy of the elevation data or parallax in the images.
For display purposes, the vertical elevations on the topographic map are referenced to an estimated local tidal datum, Mean Sea Level at Kasatochi (KMSL). The local MSL datum is a linear correction defined by the 10:21 June 15, 2009 water level at AVO benchmark KAS4 and the tidal predictions at the Fenimore Pass subordinate tidal station (9461519). Conversion factors for this local datum and common ellipsoids are: add 8.3 meters to Kasatochi MSL (map datum) to obtain WGS84 or ITRF2008 elevations (m); add 7.3 m to Kasatochi MSL (map datum) to obtain NAD83(2011) elevations (m).
This data release is complete. Note: the presence of small clouds in the original satellite images make derived elevation data in the southeast crater wall unreliable.
All data are derived from a small number of satellite images, insuring a high level of internal consistency. Data from disparate sources were not combined.
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MP 163
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| Data format: | Raster data and ArcGIS map files |
|---|---|
| Network links: |
<http://doi.org/10.14509/29733> |
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