Peer-Reviewed Articles
1353 Revised Mapping of Lava Flows on Mount
Etna, Sicily
Michael Abrams, Remo Bianchi, and Dave Pieri
Abstract
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Reports a differing approach used to determine relative ages of Etnean
lava flows. Multispectral image data were acquired from aircraft overflights
of
Etna in 1991. The Thematic Mapper Simulator instrument obtained 12 channels
of data in the visible through thermal infrared wavelength regions. Supervised
classification of these data allowed the authors to group Etnean flows into
age groups based on their spectral properties. About 90% of the classification
agrees with the mapped lava flow ages. Results generally support the paleomagnetic
age determinations for flow ages that disagree with the mapped ages. In addition,
several areas were remapped, correcting errors on the published map.
1361 The Use of Satellite and Airborne Imagery to Inventory Outlet Glaciers
of the Southern Patagonia Icefield, South America
M. Aniya, H. Sato, R. Naruse, P. Skvarca, and G. Casassa
Abstract
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A Landsat TM mosaic of the Southern Patagonia Icefield (SPI), S America, was
utilized as an image base map to inventory its outlet glaciers. Employing a
supervised classification using Landsat TM bands 1, 4, and 5, glacier drainage
basins were divided into accumulation and ablation areas, thereby determining
the position of the transient snow line (TSL). After comparing with existing
data, it was found that the TSL could be taken, for practical purposes, as
the equilibrium line (EL). The position of the TSL was then compared with topographic
maps, where available, to determine the equilibrium line altitude (ELA). Altogether,
11 parameters relating primarily to glacier morphology were inventoried. Pio
XI Glacier (1265 km"SUP 2" ) is found to be the largest outlet glacier
in S America, and may also be its longest. The average accumulation area ratio
of 0.75 is larger than those of the Northern Patagonia Icefield and European
glaciers. All but two outlet glaciers calve into fjords or pro-glacial lakes.
1371 Applications of Spectral Stratigraphy to Upper Cretaceous
and Tertiary Rocks in Southern Mexico: Tertiary Graben Control on Volcanism
Pamela E. Jansma and Harold R. Lang
Abstract
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Seven spectral stratigraphic units, each of which corresponds to a distinct
lithostratigraphic unit, were delineated. Five consist of terrestrial Upper
Cretaceous and Tertiary siliciclastic, volcanic, and volcaniclastic rocks;
one contains Mesozoic marine rocks; and one corresponds to Quaternary alluvium.
A previously undocumented NNW-trending Tertiary graben was identified in
which 2000 m of lower Tertiary volcanic rocks accumulated, suggesting volcanism
coeval with graben subsidence during WSW-ENE regional extension in the early
Tertiary. Overlap of the western-graben bounding fault by slightly younger
lower Tertiary rocks suggests subsidence ended by the close of the early
Tertiary. Continued volcanism within the graben during the late Tertiary
indicates a long-lived volcanic source region within the sub- surface of
the NNW-trending structure and localization of younger magmatic activity
within a pre- existing zone of crustal weakness.
1379 Remote Mineralogic and Lithologic Mapping of the Ice River Alkaline
Complex, British Columbia, Canada, Using AVIRIS Data
Timothy L. Bowers and Lawrence C. Rowan
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The authors examined the alkaline complex and adjacent country rocks using
Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) data. This technique
models each pixel spectrum in an AVIRIS image as a linear combination of unique
endmember spectra. Endmember spectra were selected from well-exposed and spectrally
distinct mineralogic units, vegetation, and snow. Four of the endmembers reflect
mineralogic variations within the McKay group in the study area, and may represent
lateral and vertical variations of sedimentary or metamorphic facies. Otherwise,
the resultant spatial distribution of endmembers shows generally close agreement
with the published geologic map, although, in several places, the image-map
is more accurate than the published map.
1387 Waste Site Characterization through Digital Analysis of Historical
Aerial Photographs
Paul Pope, Ed Van Eeckhout, and Cheryl Rover
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Historical aerial photographs have been used to provide a physical history
and preliminary mapping information for characterizing a Department of Energy
waste burial site at Los Alamos National Laboratory, New Mexico. The coregistered
images were studied individually (and in comparison with each other) to identify
features which were indicative of human activity at the site and to provide
a physical history of natural and human induced changes. The coregistered images
were imported to a geographic information system and geographically coded to
a common coordinate system. The geographic information system was used to extract
the boundaries of features such as suspected trenches and disturbed soil. This
preliminary analysis forms a basis for planning and comparing the results from
other remote sensing and geophysical surveys which will be used to improve
the characterization of the waste site.
1397 Use of Digital Image Analysis and GIS to Assess Regional Soil
Compaction Risk
M.L. Bober, D. Wood, and R.A. McBride
Abstract
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A soil compaction risk study was undertaken in an agricultural region of southern
Ontario, Canada. The objective was to identify land areas that are highly
susceptible to traffic- and tillage- induced soil compaction given their
soil mechanical properties and their use for intensive row crop production
(including continuous corn monoculturing) under local climatic conditions.
Spatial information on the distribution of various agricultural crops in
relation to the major soil associations was acquired using an integrated
approach involving digital image analysis and GIS. Error matrices showed
that the user's accuracy of the crop over classification at the field level
was better than 80% for all major crop types, and the correspondence to census
information was equally good. The soil associations most vulnerable to compaction
in three local municipalities where row crops dominate included about 75
km"SUP 2" of medium-textured soils. The silty clay loam tills were
identified as being particularly at risk due to observed cropping practices.