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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Planetary geomorphology field studies: Iceland and Antarctica

Field studies of terrestrial landforms and the processes that shape them provide new directions to the study of planetary features. These studies, conducted in Iceland and in Antarctica, investigated physical and chemical weathering mechanisms and rates, eolitan processes, mudflow phenomena, drainage development, and catastrophic fluvial and volcanic phenomena. Continuing investigations in Iceland fall in three main catagories: (1) catastrophic floods of the Jokulsa a Fjollum, (2) lahars associated with explosive volcanic eruptions of Askja caldera, and (3) rates of eolian abrasion in cold, volcanic deserts. The ice-free valleys of Antarctica, in particular those in South Victoria Land, have much is common with the surface of Mars. In addition to providing independent support for the application of the Iceland findings to consideration of the martian erosional system, the Antarctic observations also provide analogies to other martian phenomena. For example, a family of sand dunes in Victoria Valley are stabilized by the incorporation of snow as beds.

Malin, M. C.↗
NASA NTRS1984

Thermal infrared analysis of volcanic surfaces: Mars and Hawaii

High spatial resolution data from the Viking infrared thermal mapper (IRTM) are used to examine the Tharsis volcanoes which are situated within a vast area of low thermal inertia material very fine particle size or very high porosity, with the volcanoes having the lowest thermal inertias. Thermal infrared images of the 1823 flow on Kilauea's southwest rift zone show lower thermal inertias near the vent area where shelly pahoehoe is common while individual channelized aa flows with abundant broken pahoehoe slabs are higher thermal inertia. The increase in aa flows to the southeast leads to a general trend of increasing thermal inertias from near vent to distal areas. Martian shield volcanoes have thermal inertias equal to or higher than their surrounding plans when atmospheric effects are removed from the data. The general increase in thermal inertias away from the summit calderas is consistent with the trend of the Hawaiian 1823 flow and may be related to changing lava properties away from the summit.

Zimbelman, J. R.↗
NASA NTRS1983

Io

A report on the continuing investigation of Io is presented. Gravitational resonance is discussed as the cause of Io's volcanism, and the volcanic activity is explained in terms of sulfur chemistry. Theories concerning the reasons for the two main types of volcanic eruptions on Io are advanced and correlated with geographical features of the satellite. The sulfur and silicate models of the calderas are presented, citing the strengths and weaknesses of each. Problems of the gravitational resonance theory of Io's heat source are then described. Finally, observations of Io planned for the Galileo mission are summarized.

Johnson, T. V.↗
NASA NTRS1984

Topography of the shield volcano, Olympus Mons on Mars

Olympus Mons, one of the largest known shield volcanoes in the solar system, covers an area of more than 3.2 x 10 to the 5th sq km and has a diameter of more than 600 km, excluding its vast aureole deposits. The structure is five times larger than the largest shield volcano on the earth. It is situated on the north-west flank of the Tharsis volcanic region, a broad topographic rise on the Martian surface. The volcano has three physical subdivisions: the summit caldera, the terraced upper flanks, and the lower flanks, which terminate in a scarp 2-10 km high that nearly surrounds the structure. A large block of images of the Tharsis region, including Olympus Mons, was obtained by the Viking mission. A topographic map of Olympus Mons is presented here, which has been compiled using various combinations of stereo pairs of these images, together with stereoscopic perspective views generated by image processing techniques.

Wu, S. S. C.↗
NASA NTRS1985

Geologic Interpretation of Remote Sensing Data for the Martian Volcano, Ascraeus Mons

Results of an investigation to relate remotely determined physical properties on Ascraeus Mons to the geologic history of the volcano are summarized. Products include a 1:2,000,000-scale photogeologic map of Ascraeus Mons and its environs; a 1:250,000-scale corrected thermal-inertia map of the summit caldera complex; four corrected thermal-inertia profiles across the volcano from high-resolution thermal data; fourteen low-resolution thermal sequences providing corrected thermal inertias for the volcano throughout half a Martian year; and a calibrated three-color photograph of the volcano. These data were combined with published spectral-reflectance, radar, and atmospheric water-vapor data relating to Acraeus Mons. Photogeologic mapping indicates that the sequence of events at Acraeus Mons is more complex than previously described. The plains surrounding the volcano include numerous flows, some of which can be traced to the flank of the volcano and some to different locations along the Tharsis Ridge. Surface morphology in the summit area is very distinct for features 100 m in scale, but the surface relief and tonal contrast steadily decrease toward the base of the shield, indicating modification by deposition or erosion.

Zimbelman, J.↗
NASA NTRS1986

A study of tectonic activity in the Basin-Range Province and on the San Andreas Fault. No. 2: Lithospheric structure, seismicity, and contemporary deformation of the United States Cordillera

The structural evolution of the U.S. Cordillera has been influenced by a variety of tectonic mechanisms including passive margin rifting and sedimentation; arc volcanism; accretion of exotic terranes; intraplate magmatism; and folding and faulting associated with compression and extension processes that have profoundly influenced the lithospheric structure. As a result the Cordilleran crust is laterally inhomogeneous across its 2000 km east-west breadth. It is thin along the West Coast where it has close oceanic affinities. The crust thickens eastward beneath the Sierra Nevada, then thins beneath the Basin-Range. Crustal thickening continues eastward beneath the Colorado Plateau, the Rocky Mountains, and the Great Plains. The total lithospheric thickness attains 65 km in the Basin-Range and increases eastward beneath the Colorado Plateau. The upper-crust, including the crystalline basement of the Cordillera, has P sub G velocities of 6 km/s in the Basin-Range and Rio Grande Rift. Lower P sub G velocities of 5.4 to 5.7 km/s are associated with the youthful Yellowstone, Valles and Long Valley calderas and the Franciscan assemblage of the western coastal margin. Averaged crustal velocity reflects integrated tectonic evolution of the crust-thick silicic bodies, velocity reversals, and a thin crust produce low averaged velocities that are characteristic of a highly attenuated and thermally deformed crust.

Smith, R. B.↗
NASA NTRS1986

Geophysical characteristics and crustal structure of greenstone terranes: Canadian Shield

Geophysical studies in the Canadian Shield have provided some insights into the tectonic setting of greenstone belts. Greenstone belts are not rooted in deep crustal structures. Geophysical techniques consistently indicate that greenstones are restricted to the uppermost 10 km or so of crust and are underlain by geophysically normal crust. Gravity models suggest that granitic elements are similarly restricted, although magnetic modelling suggests possible downward extension to the intermediate discontinuity around approx. 18 km. Seismic evidence demonstrates that steeply-dipping structure, which can be associated with the belts in the upper crust, is not present in the lower crust. Horizontal intermediate discontinuities mapped under adjacent greenstone and granitic components are not noticeably disrupted in the boundary zone. Geophysical evidence points to the presence of discontinuities between greenhouse-granite and adjacent metasedimentary erranes. Measured stratigraphic thicknesses of greenstone belts are often twice or more the vertical thicknesses determined from gravity modelling. Explantations advanced for the discrepancy include stratigraphy repeated by thrust faulting and/or listric normal faulting, mechanisms which are consistent with certain aspects of conceptual models of greenstone development. Where repetition is not a factor the gravity evidence points to removal of the root zones of greenstone belts. For one region, this has been attributed to magmatic stopping during resurgent caldera activity.

Thomas, M. D.↗
NASA NTRS1986

The March 1985 demonstration of the fiducial network concept for GPS geodesy: A preliminary report

The first field tests in preparation for the NASA Global Positioning System (GPS) Caribbean Initiative were conducted in late March and Early April of 1985. The GPS receivers were located at the POLARIS Very Long Base Interferometry (VLBI) stations at Westford, Massachusetts; Richmond, Florida; and Ft. Davis, Texas; and at the Mojave, Owens Valley, and Hat Creek VLBI stations in California. Other mobile receivers were placed near Mammoth Lakes, California; Pt. Mugu, California; Austin, Texas; and Dahlgren, Virginia. These sites were equipped with a combination of GPS receiver types, including SERIES-X, TI-4100 and AFGL dual frequency receivers. The principal objectives of these tests were the demonstration of the fiducial network concept for precise GPS geodesy, the performance assessment of the participating GPS receiver types, and to conduct the first in a series of experiments to monitor ground deformation in the Mammoth Lakes-Long Valley caldera region in California. Other objectives included the testing of the water vapor radiometers for the calibration of GPS data, the development of efficient procedures for planning and coordinating GPS field exercise, the establishment of institutional interfaces for future cooperating ventures, the testing of the GPS Data Analysis Software (GIPSY, for GPS Inferred Positioning SYstem), and the establishment of a set of calibration baselines in California. Preliminary reports of the success of the field tests, including receiver performance and data quality, and on the status of the data analysis software are given.

Davidson, J. M.↗
NASA NTRS1987

Nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain, and Kane Springs, Wash volcanic centers, Southern Nevada

LANDSAT Thematic Mapper imagery was evaluated over 3 Tertiary calderas in southern Nevada. Each volcanic center derived from a highly evolved silici magmatic system represented today by well exposed diverse lithologies. Distinctive imagery contrast between some of the late ash flows and earlier units follows from the high relative reflectance in longer wavelength bands (bands 5 and 7) of the former. Enhancement techniques provide color composite images which highlight some of the units in remarkable color contrast. Inasmuch as coatings on the tuffs are incompletely developed and apparently largely dependent spectrally on rock properties independent of petrochemistry, it is felt that the distinctive imagery characteristics are more a function of primary lithologic or petrochemical properties. Any given outcrop is backdrop for a variety of cover types, of which coatings, at various stages of maturity, are one. Petrographic and X-ray diffraction analysis of the outer air-interface zone of coatings reveal they are composed chiefly of amorphous compounds, probably with varying proportions of iron and manganese. Observations support an origin for some outer (air-interface) coating constituents exogenous to the underlying host.

Taranik, James V.↗
NASA NTRS1986

Topographic evidence for shield volcanism on Io

Similarities between terrestrial shield volcanoes and a volcano on Io observed in Voyager I imagery of the satellite at 30 deg S, 246 deg W are delineated. A photoclinometry model was used to numerically estimate the slope based on the Minnaert photometric function. The slope values are accurate to within 10 deg on the sun-facing slope and 1 deg on the shadow side. As found with shield volcanoes, the feature has a central edifice, 40-50 km in diameter, and a broad, elliptical base, 77 x 90 km across. The summit of the Io volcano is 2.2-2.8 km above the surrounding plane and contains a caldera about 5 km in diameter. The similarity in shape between basaltic terrestrial shield volcanoes and the Io volcano indicates that the Io feature may also be composed of basalt. The composition could be sulfur if the heat flow was under 0.05 W/sq m, as it might have been in later stages of formation.

Moore, J. M.↗
NASA NTRS1987

Cleopatra Patera on Venus - Venera 15/16 evidence for a volcanic origin

The nonconcentric nature, anomalous depth, and terraced morphology of the nested craters that compose Cleopatra Patera are more closely analogous to volcanic craters (calderas) than multiring impact structures. Associated deposits northeast and downslope of the Patera first recognized on Venera 15/16 radar images are interpreted as volcanic plains related to, and perhaps cogenetic with, Cleopatra. The plains lavas probably originated as effusions from a radial rift zone or ring fissures. Rim deposits surrounding Cleopatra are asymmetric along the structural fabric of the region, also indicating fissure-type eruptions. Finally, a volcanic origin not only is easily reconciled with the tectonic setting of the Patera, it is almost required by the correlation between the Patera and regional structural trend.

Schaber, Gerald G.↗
NASA NTRS1987

Radar characteristics of small craters - Implications for Venus

Shuttle radar images (SIR-A) of volcanic and impact craters were examined to assess their appearance on radar images. Radar characteristics were determined for (1) nine maarlikie craters in the Pinacate volcanic field, Sonora, Mexico; (2) the caldera of Cerro Volcan Quemado, in the Bolivian Andes; (3) Talemzane impact crater, Algeria; and (4) Al Umchaimin, a possible impact structure in Iraq. SIR-A images were compared with conventional photographs and with results from field studies. Consideration was then given to radar images available for Venus, or anticipated from the Magellan mission. Of the criteria ordinarily used to identify impact craters, some can be assessed with radar images and others cannot be used; planimetric form, expressed as circularity, and ejecta-block distribution can be assessed on radar images, but rim and floor elevations relative to the surrounding plain and disposition of rim strata are difficult or impossible to determine. It is concluded that it will be difficult to separate small impact craters from small volcanic craters on Venus using radar images and is suggested that it will be necessary to understand the geological setting of the areas containing the craters in order to determine their origin.

Greeley, Ronald↗
NASA NTRS1987

On the evolution and activity of cometary nuclei

The thermal evolution of a spherical cometary nucleus, composed initially of very cold amorphous ice and moving in comet Halley's orbit, is simulated numerically for 280 revolutions. It is found that the phase transition from amorphous to crystalline ice constitutes a major internal heat source. The transitions occur in five distinct rounds, with the phase transition front advancing into the nucleus to progressively greater depths. At the time of crystallization, the temperature of the transformed ice rises to 180 K. It is argued that gas tends to accumulate in pockets that eventually explode, forming 'volcanic calderas' and exposing gas-laden amorphous ice which may be a major source of gas and dust jets into the coma. The activity of new comets and, possibly, cometary outbursts and splits may also be explained in terms of explosive gas release following the transition from amorphous to crystalline ice.

Prialnik, Dina↗
NASA NTRS1988

Nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain, and Kane Springs Wash volcanic centers, Southern Nevada

Comparative lab spectra and Thematic Mapper imagery investigations at 3 Tertiary calderas in southern Nevada indicate that desert varnish is absorbant relative to underlying host rocks below about 0.7 to 1.3 microns, depending on mafic affinity of the sample, but less absorbant than mafic host rocks at higher wavelengths. Desert varnish occurs chiefly as thin impregnating films. Distribution of significant varnish accumulations is sparse and localized, occurring chiefly in surface recesses. These relationships result in the longer wavelength bands and high 5/2 values over felsic units with extensive desert varnish coatings. These lithologic, petrochemical, and desert varnish controlled spectral responses lead to characteristic TM band relationships which tend to correlate with conventionally mappable geologic formations. The concept of a Rock-Varnish Index (RVI) is introduced to help distinguish rocks with a potentially detectable varnish. Felsic rocks have a high RVI, and those with extensive desert varnish behave differently, spectrally, from those without extensive varnish. The spectrally distinctive volcanic formations at Stonewall Mountain provide excellent statistical class segregation on supervised classification images. A binary decision rule flow-diagram is presented to aid TM imagery analysis over volcanic terrane in semi-arid environments.

Taranik, James V.↗
NASA NTRS1987

Variability in spectral signatures of terrestrial volcanic rocks and implications for volcanology on Mars

The LANDSAT Thematic Mapper (TM) studies of 2.2 my old ignimbrites in a test area around the Cerro Galan Caldera, N. W. Argentina, show that the ignimbrites exhibit a remarkable range of spectral characteristics dependent both on intrinsic and extrinsic properties resulting from aeolian weathering processes. Spectral profiles of the ignimbrite in four contrasted environments were constructed using 6 TM bands. The textural and structural characteristics of ignimbrites on Mars were evaluated.

Francis, P. W.↗
NASA NTRS1988

Mid to late proterozoic magmatism within Northeastern North America and its iplications for the growth of the continental crust

Recent studies of the mangerite-charnockite-alaskite suite exposed in the Adirondack Highlands strongly suggest that these rocks were emplaced under anorogenic, or mildly extensional, conditions. The characteristic signatures of the rocks are high (FeO/FeO+MgO) and (FeO/Fe2O3); mildly alkaline to subalkaline and metaluminous trends; high Ga/Al2O3; and within plate concentrations of Nb vs Y, Ta vs Yb, Rb vs (Y+Nb), and Rb vs (Yb+Ta). Evolved members of the series are low in CaO and MgO and high in alkalies and halogens. All of these properties are consistent with anorogenic magmatism comprising acidic crustal melts and mantle derived mafic additions to the crust. Major and minor element trends, as well as field evidence, strongly suggest that the anorogenic acidic suite is coeval, but not comagmatic, with closely associated anorthositic massifs. Present outcrop configurations are consistent with the evolution of the acidic and anorthositic rocks in zoned, bimodal magma chambers cored by the mafic constituents and overlain by explosive, caldera-type volcanism. Age determinations indicate that the emplacement of the anorthosite-charnockite suite extended over approximately 500 Ma in the Grenville and adjacent Nain, Provinces.

Mclelland, J. M.↗
NASA NTRS1988

Rifts of deeply eroded Hawaiian basaltic shields: A structural analog for large Martian volcanoes

Recently derived morphologic evidence suggests that intrusive events have not only influenced the growth of young shield volcanoes on Mars but also the distribution of volatiles surrounding these volcanoes: in addition to rift zones and flank eruptions on Arsia Mons and Pavonis Mons, melt water channels were identified to the northwest of Hecates Tholus, to the south of Hadriaca Patera, and to the SE of Olympus Mons. Melt water release could be the surface expression of tectonic deformation of the region or, potentially, intrusive events associated with dike emplacement from each of these volcanoes. In this study the structural properties of Hawaiian shield volcanoes were studied where subaerial erosion has removed a sufficient amount of the surface to enable a direct investigation of the internal structure of the volcanoes. The field investigation of dike morphology and magma flow characteristics for several volcanoes in Hawaii is reported. A comprehensive investigation was made of the Koolau dike complex that passes through the summit caldera. A study of two other dissected Hawaiian volcanoes, namely Waianae and East Molokai, was commenced. The goal is not only to understand the emplacement process and magma flow within these terrestrial dikes, but also to explore the possible role that intrusive events may have played in volcano growth and the distribution of melt water release on Mars.

Knight, Michael D.↗
NASA NTRS1989

Lithospheric buckling and intra-arc stresses: A mechanism for arc segmentation

Comparison of segment development of a number of arcs has shown that consistent relationships between segmentation, volcanism and variable stresses exists. Researchers successfully modeled these relationships using the conceptual model of lithospheric buckling of Yamaoka et al. (1986; 1987). Lithosphere buckling (deformation) provides the needed mechanism to explain segmentation phenomenon; offsets in volcanic fronts, distribution of calderas within segments, variable segment stresses and the chemical diversity seen between segment boundary and segment interior magmas.

Nelson, Kerri L.↗