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At least 415 records · Page 23

Geologic Provinces Beneath the Greenland Ice Sheet Constrained by Geophysical Data Synthesis

Present understanding of Greenland's subglacial geology is derived mostly from interpolation of geologic mapping of its ice-free margins and unconstrained by geophysical data. Here we refine the extent of its geologic provinces by synthesizing geophysical constraints on subglacial geology from seismic, gravity, magnetic and topographic data. North of 72°N, no province clearly extends across the whole island, leaving three distinct subglacial regions yet to be reconciled with margin geology. Geophysically coherent anomalies and apparent province boundaries are adjacent to the onset of faster ice flow at both Petermann Glacier and the Northeast Greenland Ice Stream. Separately, based on their subaerial expression, dozens of unusually long, straight and sub-parallel subglacial valleys cross Greenland's interior and are not yet resolved by current syntheses of its subglacial topography.

Joseph A. MacGregor↗

Documenting volcano-tectonic episodes in Mars' stratigraphic record

Global geologic maps of Mars at 1:15,000,000 scales were digitized to obtain accurate measurements of the areal extent of 90 geologic units. These data were used to determine the resurfacing history of Mars by volcanic, eolian, fluvial, periglacial, and impact processes. This work is presently being extended to focus on the extent, magnitude, and duration of volcanism and tectonism (mainly faulting) throughout each of the three time-stratigraphic systems. This work involves detailed mapping to assess volcano-tectonic episodes in terms of their occurrence in eight epochs that represent subdivisions of Martian periods.

Scott, David H.↗

Mapping of lithologic and structural units using multispectral imagery

The author has identified the following significant results. ERTS-1 MSS imagery covering the Afar-Triangle/Ethiopia and adjacent regions (Ethiopian Plateau, Somali Plateau, and parts of Yemen and Saudi Arabi) was applied to the mapping of lithologic and structural units of the test area at a scale 1:1,000,000. Results of the geological evaluation of the ERTS-1 imagery of the Afar have proven the usefullness of this type of satellite data for regional geological mapping. Evaluation of the ERTS images also resulted in new aspects of the structural setting and tectonic development of the Afar-Triangle, where three large rift systems, the oceanic rifts of the Red Sea and Gulf of Aden and the continental East African rift system, seem to meet each other. Surface structures mapped by ERTS do not indicate that the oceanic rift of the Gulf of Aden (Sheba Ridge) continues into the area of continental crust west of the Gulf of Tadjura. ERTS data show that the Wonji fault belt of the African rift system does not enter or cut through the central Afar. The Aysha-Horst is not a Horst but an autochthonous spur of the Somali Plateau.

Kronberg, P.↗

Intercrater plains deposits and the origin of Martian valleys

Detailed geological mapping of portions of the Thaumasia Fossae and Aeolis Quandrangles has documented several interesting relationships between valley development and local geology. Formation of the valley development was discussed.

Brakenridge, G. R.↗

Exploitation of ERTS-1 imagery utilizing snow enhancement techniques

Photogeological analysis of ERTS-simulation and ERTS-1 imagery of snowcovered terrain within the ERAP Feather River site and within the New England (ERTS) test area provided new fracture detail which does not appear on available geological maps. Comparative analysis of snowfree ERTS-1 images has demonstrated that MSS Bands 5 and 7 supply the greatest amount of geological fracture detail. Interpretation of the first snow-covered ERTS-1 images in correlation with ground snow depth data indicates that a heavy blanket of snow (more than 9 inches) accentuates major structural features while a light "dusting", (less than 1 inch) accentuates more subtle topographic expressions. An effective mail-based method for acquiring timely ground-truth (snowdepth) information was established and provides a ready correlation of fracture detail with snow depth so as to establish the working limits of the technique. The method is both efficient and inexpensive compared with the cost of similarly scaled direct field observations.

Wobber, F. J.↗

Highland Valley Networks and Ephemeral Lake Basins, Libya Montes, SW Isidis Basin Margin

This summarizes the analysis of geology and surface engineering criteria for an area on the southwestern border of Isidis Planitia. In this area basin plains adjoin volcanic plains of Syrtis Major Planum and dissected ancient highlands of Libya Montes. Previously three general categories of landing site have been discussed for this area: scarp-like terrain along the western margin of Isidis Planitia, marginal ridged plains, and terminus of a significant valley network basin draining Libya Montes. On the basis of geologic mapping and reconnaissance around the southwest perimeter, the plains marginal slopes adjacent to Libya Montes appear to best satisfy the thematic, geologic, and engineering goals and constraints of the Mars Surveyor program.

Crumpler, L. S.↗

High resolution thermal infrared mapping of Martian channels

Viking Infrared Thermal Mapper (IRTM) high resolution (2 to 5 km) data were compiled and compared to Viking Visual Imaging Subsystem (VIS) data and available 1:5M geologic maps for several Martian channels including Dao, Harmakhis, Mangala, Shalbatana, and Simud Valles in an effort to determine the surface characteristics and the processes active during and after the formation of these channels. Results show a dominance of aeolian processes active in and around the channels. These processes have left materials thick enough to mask any genuine channel deposits. Results also indicate that very comparable Martian channels and their surrounding terrain are blanketed by deposits which are homogeneous in their thermal inertia values. However, optimum IRTM data does not cover the entire Martian surface and because local deposits of high thermal inertia material may not be large enough in areal extent or may be in an unfavorable location on the planet, a high resolution data track may not always occur over these deposits. Therefore, aeolian processes may be even more active than the IRTM data tracts can always show.

Craddock, R. A.↗

The Fredegonde (V-57) Quadrangle, Venus: Characterization of the Venus Midlands

The Fredegonde quadrangle (V-57, 50-75degS, 60-120degE) in the southern hemisphere of Venus represents a typical region of midlands (0-2 km above MPR). Midlands are the most widespread topographic province on Venus (approx.80%) and display the richest variety of features. Geological mapping in the V-57 quadrangle provides the possibility of defining and characterizing units that make up a region of midlands and to establish the general sequence of events there and thus address questions about the modes of formation and chronology of midlands on Venus. The map area is in contact with the uplands in the central portion of Lada Terra to the west and the lowlands of Aino Planitia to the northeast. This position also provides a transitional zone between the other two major topographic provinces, similar to that of the Meskhent Tessera (V-3) area. Here we report on the results of our mapping in the V-57 quadrangle, describe the major features, units, and structural assemblages exposed there, and outline the main episodes of geologic history.

Ivanov, M. A.↗

Multidisciplinary study on Wyoming test sites

The author has identified the following significant results. Ten EREP data passes over the Wyoming test site provided excellent S190A and S190B coverage and some useful S192 imagery. These data were employed in an evaluation of the EREP imaging sensors in several earth resources applications. Boysen Reservoir and Hyattsville were test areas for band to band comparison of the S190 and S192 sensors and for evaluation of the image data for geologic mapping. Contrast measurements were made from the S192 image data for typical sequence of sedimentary rocks. Histograms compiled from these measurements show that near infrared S192 bands provide the greatest amount of contrast between geologic units. Comparison was also made between LANDSAT imagery and S190B and aerial photography for regional land use mapping. The S190B photography was found far superior to the color composite LANDSAT imagery and was almost as effective as the 1:120,000 scale aerial photography. A map of linear elements prepared from LANDSAT and EREP imagery of the southwestern Bighorn Mountains provided an important aid in defining the relationship between fracture and ground water movement through the Madison aquifer.

Houston, R. S.↗

Erosional and depositional history of central Chryse Planitia

This map uses high resolution image data to assess the detailed depositional and erosional history of part of Chryse Planitia. This area is significant to the study of the global geology of Mars because it represents one of only two areas on the martian surface where planetary geologic mapping is assisted with 'ground truth.' In this case the ground truth was provided by Viking Lander 1. Additional questions addressed in this study are concerned with the following: the geologic context of the regional plains surface and the local surface of the Viking Lander 1 site; and the relative influence of volcanic, sedimentary, impact, aeolian, and tectonic processes at the regional and local scales.

Crumpler, L. S.↗

Effects of structure and volcanic stratigraphy on groundwater and surface water flow: Hat Creek basin, California, USA

Abstract Hydrogeologic systems in the southern Cascade Range in California (USA) develop in volcanic rocks where morphology, stratigraphy, extensional structures, and attendant basin geometry play a central role in groundwater flow paths, groundwater/surface-water interactions, and spring discharge locations. High-volume springs (greater than 3 m 3 /s) flow from basin-filling (<800 ka) volcanic rocks in the Hat Creek and Fall River tributaries and contribute approximately half of the average annual flow of the Pit River, the largest tributary to Shasta Lake. A hydrogeologic conceptual framework is constructed for the Hat Creek basin combining new geologic mapping, water-well lithologic logs, a database of active faults, LiDAR mapping of faults and volcanic landforms, streamflow measurements and airborne thermal infrared remote sensing of stream temperature. These data are used to integrate the geologic structure and the volcanic and volcaniclastic stratigraphy to create a three-dimensional interpretation of the hydrogeology in the basin. Two large streamflow gains from focused groundwater discharge near Big Spring and north of Sugarloaf Peak result from geologic barriers that restrict lateral groundwater flow and force water into Hat Creek. The inferred groundwater-flow barriers divide the aquifer system into at least three leaky compartments. The two downstream compartments lose streamflow in the upstream reaches (immediately downstream of the groundwater-flow barriers) and gain in downstream reaches with the greatest inflows immediately upstream of the barriers.

Geology↗

Utilization of ERTS-1 data in North Carolina

The author has identified the following significant results. Initial study and interpretation of ERTS-1 imagery indicates its usefulness for regional land use planning purposes in North Carolina. Quarries, many secondary roads, and the existence of urbanization as well as changes in urban areas may be mapped. Differences in spectral response for various parts of the major cities suggests that the type of activity in urbanized areas may be monitored. Geological mapping at a scale of 1:250,000 may be possible. The major unfavorable comment from various organizations and agencies who are potential users has been to the relatively small scale. The imagery is a powerful illustrative tool for the several state agencies cooperating in the investigation.

Welby, C. W.↗

Spectroscopic remote sensing for geological applications

Remote sensing is being used with increasing frequency in the development of geologic maps and in the exploration process. Spectral data from airborne and spaceborne multispectral scanners provide information on rock type and vegetation stress, important in geologic applications. Emphasis is now being placed on direct identification of materials rather than discrimination among geologic units. To do this, higher spectral resolution systems with wider spectral coverage than currently available are required. Imaging spectroscopy in the 0.4 - 14 microns region appears to be the answer.

Goetz, A. F. H.↗

First Use of an Airborne Thermal Infrared Hyperspectral Scanner for Compositional Mapping

In May 1999, the airborne thermal infrared hyperspectral imaging system, Spatially Enhanced Broadband Array Spectrograph System (SEBASS), was flown over Mon-non Mesa, NV, to provide the first test of such a system for geological mapping. Several types of carbonate deposits were identified using the 11.25 microns band. However, massive calcrete outcrops exhibited weak spectral contrast, which was confirmed by field and laboratory measurements. Because the weathered calcrete surface appeared relatively smooth in hand specimen, this weak spectral contrast was unexpected. Here we show that microscopic roughness not readily apparent to the eye has introduced both a cavity effect and volume scattering to reduce spectral contrast. The macroroughness of crevices and cobbles may also have a significant cavity effect. The diminished spectral contrast is important because it places higher signal-to-noise ratio (SNR) requirements for spectroscopic detection and identification. This effect should be factored into instrumentation planning and interpretations, especially interpretations without benefit of ground truth. SEBASS had the required high SNR and spectral resolution to allow us to demonstrate for the first time the ability of an airborne hyperspectral thermal infrared scanner to detect and identify spectrally subtle materials.

Kirkland, Laurel↗

The geologic evolution of Imdr Regio: a possible active hot spot on Venus

Imdr Regio is a large igneous rise that extends approximately from 35ºS-50ºS and 195ºE-225ºE between the plains of Helen, Nsomeka and Wawalag Planitiae. Imdr Regio was classified as a volcano-dominated igneous rise with a minimum-maximum diameter of 1200-1400 km and a swell height of 1.6 km. The major volcanic feature in Imdr Regio is Idunn Mons (46.5ºS/214.5ºE), a large volcano. Studies using the 1 mm (derived) surface emissivity from the Venus Express mission of the volcanic flows surrounding Idunn Mons suggest that high emissivity values in the volcano flanks are related to relatively unweathered basaltic rock and therefore indicative of a recent or even ongoing volcanic activity in Idunn Mons. Building on this previous work, here we present the first preliminary geologic map of Imdr Regio, characterize the different types of volcanism besides Idunn Mons, and their relationship with the rift and other regional structures, and discuss its geologic evolution.

I. López↗

Analysis of Selected Publicly Available Geothermal Exploration Data Gaps

As part of a United States Department of Energy (DOE) supported retrospective analysis of DOE's Play Fairway Analysis (PFA) projects, the National Renewable Energy Laboratory (NREL) compiled and analyzed publicly available geothermal exploration datasets to identify and highlight data gaps in areas prospective for hosting geothermal resources. The analysis was intended to understand the existing geographic coverage of selected datasets commonly utilized both by the PFA projects and geothermal developers during resource assessments including geologic mapping, temperature gradient drilling, and aeromagnetic, gravimetric, and lidar surveys. Results indicate that broad areas of the western United States estimated to have geothermal potential lack sufficient geologic and geophysical coverage necessary for even regional resource exploration. The study directly informed the recent Geoscience Data Acquisition for Western Nevada, or GeoDAWN - which united DOE's Geothermal Technologies Office (GTO) with the U.S. Geological Survey (USGS) of the U.S. Department of the Interior to assist U.S. needs for energy and critical minerals. The study also has the potential to inform public investment in further data acquisition for characterization of the Earth both for geothermal and other natural resource assessments.

data↗

Geologic applications of Space Shuttle photography

Space Shuttle astronauts have used handheld cameras to take about 30,000 photographs of the earth as seen from orbit. These pictures provide valuable, true-color depictions of many geologically significant areas. While the photographs have areal coverages and resolutions similar to the more familiar Landsat MSS and TM images, they differ from the latter in having a wide variety of solar illumination angles and look angles. Astronaut photographs can be used as very small scale aerial photographs for geologic mapping and planning logistical support for field work. Astronaut photography offers unique opportunities, because of the intelligence and training of the on-orbit observer, for documenting dynamic geologic activity such as volcanic eruptions, dust storms, etc. Astronauts have photographed more than 3 dozen volcanic eruption plumes, some of which were not reported otherwise. The stereographic capability of astronaut photography also permits three-dimensional interpretation of geologic landforms which is commonly useful in analysis of structural geology. Astronauts have also photographed about 20 known impact craters as part of project to discover presently unknown examples in Africa, South America, and Australia.

Wood, Charles A.↗