Vegetative and geologic mapping of the Western Seward Peninsula, Alaska, based on ERTS-1 imagery
Vegetative and geologic mapping of Western Seward Peninsula, Alaska, based on ERTS-1 imagery
Anderson, J. H.↗
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Vegetative and geologic mapping of the western Seward Peninsula, Alaska, based on ERTS-1 imagery
ERTS-1 scene 1009-22095 (Western Seward Peninsula, Alaska) has been studied, partly as a training exercise, to evaluate whether direct visual examination of individual and custom color-composite prints can provide new information on the vegetation and geology of this relatively well known area of Alaska. The vegetation analysis reveals seven major vegetation types, only four of which are described on existing vegetation maps. In addition, the ERTS analysis provides greater detail than the existing maps on the areal distribution of vegetation types. The geologic analysis demonstrates that most of the major rock units and geomorphic boundaries shown on the available geologic maps could also be identified on the ERTS data. Several major high-angle faults were observed, but the zones of thrust faults which are much less obvious.
Anderson, J. H.↗
A new vegetation map of the western Seward Peninsula, Alaska, based on ERTS-1 imagery
The author has identified the following significant results. A reconstituted, simulated color-infrared ERTS-1 image covering the western Seward Peninsula was prepared and it is used for identifying and mapping vegetation types by direct visual examination. The image, NASA ERTS E-1009-22095, was obtained approximately at 1110 hours, 165 degrees WMT on August 1, 1972. Seven major colors are identified. Four of these are matched with units on existing vegetation maps: bright red - shrub thicket; light gray-red - upland tundra; medium gray-red - coastal coastal wet tundra; gray - alpine barrens. The three colors having no map equivalents are tentatively interpreted as follows: pink - grassland tundra; dark gray-red - burn scars; light orange-red - senescent vegetation. A vegetation map, drawn by tracing on an acetate overlay of the image is presented. Significantly more information is depicted than on existing maps with regards to vegetation types and their areal distribution. Furthermore the preparation of the new map from ERTS-1 imagery required little time relative to conventional methods and extent of areal coverage.
Anderson, J. H.↗
Calderas produced by hydromagmatic eruptions through permafrost in northwest Alaska
Most hydromagmatic eruptions on Earth are generated by interactions of lava and ground or surface water. This eruptive process typically produces craters 0.1-1 km in diameter, although a few as large as 1-2 km were described. In contrast, a series of Pleistocene hydromagmatic eruptions through 80-100-m-thick permafrost on the Seward Peninsula of Alaska produced four craters 3-8 km in diameter. These craters, called the Espenberg maars, are the four largest maars known on Earth. The thermodynamic properties of ground ice influence the rate and amount of water melted during the course of the eruption. Large quantities of water are present, but only small amounts can be melted at any time to interact with magma. This would tend to produce sustained and highly explosive low water/magma (fuel-coolant) ratios during the eruptions. An area of 400 km(sub 2) around the Alaskan maars shows strong reductions in the density of thaw lakes, ground ice, and other surface manifestations of permafrost because of deep burial by coeval tephra falls. The unusually large Espenberg maars are the first examples of calderas produced by hydromagmatic eruptions. These distinctive landforms can apparently be used as an indicator of the presence of permafrost at the time of eruption.
Beget, J. E.↗
ERTS-A data as a teaching and research tool in the Department of Geology
The author has identified the following significant results. ERTS-1 prints have been used extensively in a geology of Alaska class to give a basic framework of the geology of the state. In addition, they have been intermittantly used in such diverse classes as: (1) Economic Geology (e.g. the Sn-bearing granites of the Seward Peninsula are particularly noticeable due to their wide contact metamorphic aureoles.) (2) A canned geology of Alaska lecture which has been given to two different introductory geology courses. (3) Structural Geology (e.g. the Fairweather and Denali faults are striking obvious). It was found most convenient for larger classes to prepare 35mm slides of the ERTS-1 prints that are used in conjunction with slides of the topographic and geologic maps at about the same scale. Thus the emphasis has been in integration of the ERTS-1 material into existing courses. As such, the ERTS-1 data has provided a unique and striking viewpoint that never fails to initiate favorable comment. In addition, prints have been examined by numerous researchers to develop a regional, integrated overview of such varied topics as regional geology to a background for local geologic mapping to studies of ore deposits and to the definition of a formation to be studied in detail at its type locality.
Grybeck, D.↗
Uplift of the Kenai Peninsula, Alaska, since the 1964 Prince William Sound earthquake
Using Global Positioning System (GPS) receivers, we reoccupied several leveling benchmarks on the Kenai Peninsula of Alaska which had been surveyed by conventional leveling immediately following the March 27, 1964, Prince William Sound earthquake (M(sub w) = 9.3). By combining the two sets of measurements with a new, high-resolution model of the geoid in the region, we were able to determine the cumulative 1993-1964 postseismic vertical displacement. We find uplift at all of our benchmarks, relative to Seward, Alaska, a point that is stable according to tide gauge data. The maximum uplift of about 1 m occurs near the middle of the peninsula. The region of maximum uplift appears to be shifted northwest relative to the point of maximum coseismic subsidence. If we use tide gauge data at Nikishka and Seward to constrain the vertical motion, then the observed uplift has a trenchward tilt (down to the southeast) as well as an arching component. To explain the observations, we use creep-at-depth models. Most acceptable models require a fault slip of about 2.75 m, although this result is not unique. If the slip has been continuous since the 1964 earthquake, then the average slip rate is nearly 100 mm/yr, twice the plate convergence rate. Comparing the net uplift achieved in 29 years with that observed over 11 years in an adjacent region southeast of Anchorage, Alaska, we conclude that the rate of uplift is decreasing. A further decrease in the uplift rate is expected as the 29-year averaged displacement rate is about twice the plate convergence rate and therefore cannot be sustained over the entire earthquake cycle.
Cohen, Steven↗
Identification, definition and mapping of terrestrial ecosystems in interior Alaska
The author has identified the following significant results. A reconstituted color infrared image covering the western Seward Peninsula was used for identifying vegetation types by simple visual examination. The image was taken by ERTS-1 approximately 1120 hours on August 1, 1972. Seven major colors were identified. Four of these were matched with four units on existing vegetation maps: bright red - shrub thicket; light gray-red - upland tundra; medium gray-red - coastal wet tundra; gray - alpine barrens. In the bright red color, two phases, violet and orange, were recognized and tentatively ascribed to differences in species composition in the shrub thicket type. The three colors which had no map unit equivalents were interpreted as follows: pink - grassland tundra; dark gray-red - burn scars; light orange-red - senescent vegetation. It was concluded that the image provides a considerable amount of information regarding the distribution of vegetation types, even at so simple a leval of analysis. It was also concluded that sequential imagery of this type could provide useful information on vegetation fires and phenologic events.
Anderson, J. H.↗
Reindeer ranges inventory in western Alaska
The use of LANDSAT data as a tool for reindeer range inventory on the tundra of northwestern Alaska is addressed. The specific goal is to map the range resource and estimate plant productivity of the Seward Peninsula. Information derived from these surveys is needed to develop range management plans for reindeer herding and to evaluate potential conflicting use between reindeer and caribou. The development of computer image classification techniques is discussed.
George, T. H.↗
On vegetation mapping in Alaska using LANDSAT imagery with primary concerns for method and purpose in satellite image-based vegetation and land-use mapping and the visual interpretation of imagery in photographic format
The author has identified the following significant results. A simulated color infrared LANDSAT image covering the western Seward Peninsula was used for identifying and mapping vegetation by direct visual examination. The 1:1,083,400 scale print used was prepared by a color additive process using positive transparencies from MSS bands 4, 5, and 7. Seven color classes were recognized. A vegetation map of 3200 sq km area just west of Fairbanks, Alaska was made. Five colors were recognized on the image and identified to vegetation types roughly equivalent to formations in the UNESCO classification: orange - broadleaf deciduous forest; gray - needleleaf evergreen forest; light violet - subarctic alpine tundra vegetation; violet - broadleaf deciduous shrub thicket; and dull violet - bog vegetation.
Anderson, J. H.↗
Postseismic Deformation after the 1964 Great Alaskan Earthquake: Collaborative Research with Goddard Space Flight Center
The purpose of this project was to carry out GPS observations on the Kenai Peninsula, southern Alaska, in order to study the postseismic and contemporary deformation following the 1964 Alaska earthquake. All of the research supported in this grant was carried out in collaboration with Dr. Steven Cohen of Goddard Space Flight Center. The research funding from this grant primarily supported GPS fieldwork, along with the acquisition of computer equipment to allow analysis and modeling of the GPS data. A minor amount of salary support was provided by the PI, but the great majority of the salary support was provided by the Geophysical Institute. After the expiration of this grant, additional funding was obtained from the National Science Foundation to continue the work. This grant supported GPS field campaigns in August 1995, June 1996, May-June and September 1997, and May-June 1998. We initially began the work by surveying leveling benchmarks on the Kenai peninsula that had been surveyed after the 1964 earthquake. Changes in height from the 1964 leveling data to the 1995+ GPS data, corrected for the geoid-ellipsoid separation, give the total elevation change since the earthquake. Beginning in 1995, we also identified or established sites that were suitable for long-term surveying using GPS. In the subsequent annual GPS campaigns, we made regular measurements at these GPS marks, and steadily enhanced our set of points for which cumulative postseismic uplift data were available. From 4 years of Global Positioning System (GPS) measurements, we find significant spatial variations in present-day deformation between the eastern and western Kenai peninsula, Alaska. Sites in the eastern Kenai peninsula and Prince William Sound move to the NNW relative to North America, in the direction of Pacific-North America relative plate motion. Velocities decrease in magnitude from nearly the full plate rate in southern Prince William Sound to about 30 mm/yr at Seward and to about 5 mm/yr near Anchorage. In contrast, sites in the western Kenai peninsula move to the SW, in a nearly trenchward direction, with a velocity of about 20 mm/yr. The data are consistent with the shallow plate interface offshore and beneath the eastern Kenai and Prince William Sound being completely locked or nearly so, with elastic strain accumulation resulting in rapid motion in the direction of relative plate motion of sites in the overriding plate. The velocities of sites in the western Kenai, along strike to the southwest, are opposite in sign with those predicted from elastic strain accumulation. These data are incompatible with a significant locked region in this segment of the plate boundary. Trenchward velocities are found also for some sites in the Anchorage area. We interpret the trenchward velocities as being caused by a continuing postseismic transient from the 1964 great Alaska earthquake.
Freymueller, Jeffrey T.↗
Crustal Uplift in the Southcentral Alaska Subduction Zones: A New Analysis and Interpretation of Tide Gauge Observations
We have examined the sea level height tide records at seven tide gauge sites in the region of southcentral Alaska that were affected by the 1964 Prince William Sound earthquake to determine the history of crustal uplift subsequent to the earthquake. There is considerable variation in the behavior depending on the location of the site relative to the 1964 rupture. At Seward, on the eastern side of the Kenai Peninsula we find a slow uplift that is consistent with elastic strain accumulation while at Seldovia and Nikiski on the western side of the Kenai we find a persistent rapid uplift of about 1 cm/yr that most likely represents a long term transient response to the earthquake, but which cannot be sustained over the expected recurrence interval for a great earthquake of several hundred years. Further to the southwest, at Kodiak, we find evidence that the rate of uplift, which is still several mm/yr, has slowed significantly over the past three and a half decades. To the east of the Kenai Peninsula we find subsidence at Cordova and an uncertain behavior at Valdez. At both of these sites there is a mathematically significant time-dependence to the uplift behavior, but the data confirming this time dependence are not as convincing as at Kodiak. At Anchorage, to the north there is little evidence of vertical motion since the earthquake. We compare these long term tide gauge records to recent GPS observations. In general there is reasonable consistency except at Anchorage and Cordova where the GPS measurement indicate somewhat more rapid uplift and subsidence, respectively.
Cohen, Steven C.↗