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At least 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Polar wandering on Mars.

Discussion of the possible wandering of the Martian spin axis during the past 100 million years suggested by the unique quasi circular structures in the polar regions of Mars. Polar wandering on Mars is likely if deep convection is involved in the origin of the very large constructional volcanic features located near the equator. The magnitude of the nonhydrostatic low order components of the gravity field and their correlation with the equatorial volcanic features may be additional evidence of deep convection and associated polar wandering.-

Murray, B. C.↗
NASA NTRS1973

Mars - Evidence for dynamic processes from Mariners 6 and 7.

Detailed study of the evolution of the Martian surface on the basis of an analysis of Mariner 6 and 7 photographs of certain features of the equatorial region of Mars. It is concluded that the planet Mars is characterized by an internal dynamic activity on the scale of the interior of the African plate. Cited as evidence are scarps resembling fault scarps in Meridiani Sinus and on the Hellas-Hellespontus border. Ridges associated with craters on the boundary of Hellas and Hellespontus are most easily explained by volcanic activity, and at least some of the associated craters may themselves be of volcanic origin. Ridges on the Hellas-Hellespontus border and part of the wall of Edom seem to bulge out into cratered swellings or domes. A sequence of events is worked out for different parts of Mars, and an attempt is made to develop a crude threefold geologic time scale. The sequence suggests that dynamic activity was confined neither to the earliest nor the latest periods of Martian history.

Elston, W. E.↗
NASA NTRS1973

Satellite geological and geophysical remote sensing of Iceland

The author has identified the following significant results. Under a binational, multidisciplinary experiment ERTS-1 imagery is being used to measure and map dynamic natural phenomena in Iceland. A few of the initial results from the project are: (1) a large variety of geological and volcanic features can be studied, particularly on imagery acquired at low sun angle ( 10 deg), which have not been previously recognized; (2) under optimum snow cover conditions, geothermal areas can be discerned by their snowmelt pattern or by warm spring discharge into frozen lakes; (3) a variety of map types at scale of 1:1,000,000 and 1:500,000, can be compiled, made more accurate, or updated (changes in coastline, glaciers, lakes, etc.); (4) the persistence of snow in the highland areas, during the summer months, has important ramifications to rangeland management; (5) false color composites (MSS) permitted the mapping of four types of vegetation; forested, reclaimed, cultivated areas and grasslands, and the mapping of the seasonal change of the vegetation, all of high value to rangeland management when complete, repetitive coverage of Iceland becomes a reality with an operational satellite; and (6) the volcanic eruption on Heimaey was recorded.

Williams, R. S., Jr.↗
NASA NTRS1973

Glaciological and volcanological studies in the Wrangell Mountains, Alaska

The author has identified the following significant results. A field trip was made to the summit of Mt. Wrangell to verify conclusions reached by study of ERTS-1 imagery and aerial photographs. Twelve points were surveyed on the snow surface of the north crater from two primary control points established in 1961-1965 on the rim. The snow surface has dropped by about 20m in the western half of the crater since 1965. In the eastern half the settling is much greater. The total amount of ice which has melted by volcanic heat appears close to 18 x 10 to the 9th power Kg. The heat flux calculated from this estimate over the 500,000 sq m area of the crater is slightly more than 1000 microcal/sq cm/sec. It is now clear that the increase in rock area observed on ERTS-1 images is due entirely to volcanic heat.

Benson, C. S.↗
NASA NTRS1973

Satellite geological and geophysical remote sensing of Iceland: Preliminary results of geologic, hydrologic, oceanographic, and agricultural studies with ERTS-1 imagery

The author has identified the following significant results. The wide variety of geological and geophysical phenomena which can be observed in Iceland, and particularly their very direct relation to the management of the country's natural resources, has provided great impetus to the use of ERTS-1 imagery to measure and map the dynamic natural phenomena in Iceland. MSS imagery is being used to study a large variety of geological and geophysical eruptive products, geologic structure, volcanic geomorphology, hydrologic, oceanographic, and agricultural phenomena of Iceland. Some of the preliminary results from this research projects are: (1) a large number of geological and volcanic features can be studied from ERTS-1 imagery, particularly imagery acquired at low sun angle, which had not previously been recognized; (2) under optimum conditions the ERTS-1 satellite can discern geothermal areas by their snow melt pattern or warm spring discharge into frozen lakes; (3) various maps at scales of 1:1 million and 1:500,000 can be updated and made more accurate with ERTS-1 imagery; (4) the correlation of water reserves with snowcover can improve the basis for planning electrical production in the management of water resources; (5) false-color composites (MSS) permitted the mapping of four types of vegetation: forested; grasslands, reclaimed, and cultivated areas, and the seasonal change of the vegetation, all of high value to rangeland management.

Williams, R. S., Jr.↗
NASA NTRS1974

Geology of the island of Hawaii

The account of the geology of the individual Hawaiian islands is only a progress report based very largely on the uppermost, visible parts of the Hawaiian volcanic range. The island of Hawaii today consists of five volcanic mountains. All of them are very young, and three of the volcanoes have been active in historic times. At least two other volcanoes which helped to build the island have been buried by more recent ones. Rocks exposed in the cliffs on the northeastern side of Kohala Mountain have been shown by the potassium-argon method to be about 700,000 years old.

Macdonald, G. A.↗
NASA NTRS1974

Mauna Iki and the Kaju Desert: Kilauea Volcano, Hawaii

The Ka'u Desert lies southwest of Kilauea Volcano. The region contains some of the most interesting and best preserved volcanic features found in the islands. The structural setting and synopsis of recent volcanic activity on the Ka'u Desert are discussed here, and a field guide to Mauna Iki is provided.

Cruikshank, D. P.↗
NASA NTRS1974

Mauna Kea

Mauna Kea, the highest of Hawaii's five volcanoes, is the only high landmass in the central Pacific Ocean basin to bear unmistakable signs of Pleistocene glaciation. The stratigraphic record indicates that a summit ice cap formed and disappeared at least four times in the last 250,000 years, and that volcanic eruptions characterized not only the interglacial intervals, but also two of the glacial periods as well. Exposed rock units on the upper slopes of Mauna Kea have been divided into two major groups based on gross lithologic character. The Hamakua Group comprises the bulk of the subaerial shield of the volcano and consists largely of thin-bedded pahoehoe flows of olivine basalt. The overlying Laupahoehoe Group consists of a thin cap of alkalic lavas and pyroclastic layers confined largely to the upper slopes of the mountain. Interstratified with the volcanic units are sedimentary formations that provide evidence of four episodes of ice cap glaciation.

Porter, S. C.↗
NASA NTRS1974

East Puna

This field trip mostly involves volcanic features that can be seen from roads in the east Puna District. Most of the features are associated with the eruptions of 1750(?), 1790(?), 1840, 1955, 1960, and the recent flows from Mauna Ulu on the Keauhou Lava Plains during the years 1969 to 1973. Particular emphasis is given to the 1955 and 1960 volcanic activity that occurred near the village of Kapoho.

Macdonald, G. A.↗
NASA NTRS1973

Geologic setting of Apollo 16

Prior to the Apollo 16 mission, the materials of the Cayley Plains and the Descartes Mountains were thought to be mostly of volcanic origin. Rock and soil samples from these regions strongly suggest, however, that they may be products of multiring basin forming impacts, although minor local volcanism is not precluded. The smooth planar surfaces may have been formed initially by Imbrium ejecta which flowed into topographic lows at the distal margins of the lineated Fra Mauro ejecta. It is emphasized, however, that the rocks and soils returned from the Apollo 16 site cannot necessarily be considered representative of the lunar crust in the Descartes region from which they were collected.

Hodges, C. A.↗
NASA NTRS1973

Analysis of lunar mare geology from Apollo photography

Panoramic and metric photography of the lunar surface from Apollo missions 15, 16, and 17 is the basis for descriptions and interpretations of mare surface features. It is suggested that the formation of mare ridges occurred over an extended period of time rather than in single short episodes of activity through faulting, flexuring, volcanism, and plutonism. Spatial relationships between rilles and ridges suggest they were formed both simultaneously and sequentially. The sinuous rilles may have developed as open lava channels or collapsed lava tubes, while the straight rilles may have been formed by fracturing. It is inferred that small scale volcanism and tectonism have occurred between major flooding episodes.

Young, R. A.↗
NASA NTRS1974

Excess europium content in Precambrian sedimentary rocks and continental evolution

It is proposed that the europium excess in Precambrian sedimentary rocks, relative to those of younger age, is derived from volcanic rocks of ancient island arcs, which were the source materials for the sediments. Precambrian sedimentary rocks and present-day volcanic rocks of island arcs have similar REE patterns, total REE abundances, and excess Eu, relative to the North American shale composite. The present upper crustal REE pattern, as exemplified by that of sediments, is depleted in Eu, relative to chondrites. This depletion is considered to be a consequence of development of a granodioritic upper crust by partial melting in the lower crust, which selectively retains europium.

Jakes, P.↗
NASA NTRS1974

Possible lunar ring dikes

A search for lunar features that showed characteristics of terrestrial ring dikes was conducted, using the Lunar Orbiter series of photographs. Features exhibiting one or more of the following four criteria were included as lunar analogs to terrestrial ring dikes: (1) inner ridges approximately concentric with the crater wall, (2) inner rills approximately concentric with the crater wall, (3) outer ridges and/or rills approximately concentric with the crater wall, and (4) interior and exterior slopes of the crater wall approximately equal. Features exhibiting each of the four criteria were found, and some had combinations of two or more including rills merging into ridges - e.g., in Taruntius and Posidonius. Gambart is an example of equal inner and outer slopes, while Hesiodus A and Marth are two of the best examples of complete inner rings concentric with the outer rings. Ten per cent of the candidates were probable impact craters but had subsequent volcanic activity of a ring dike nature. The initial search showed a distribution of the possible lunar ring dikes that was nonrandom and strongly associated with the margins of the maria, further implying that they are volcanic features.

Cameron, W. S.↗
NASA NTRS1974

Multivariate analyses of crater parameters and the classification of craters

Multivariate analyses were performed on certain linear dimensions of six genetic types of craters. A total of 320 craters, consisting of laboratory fluidization craters, craters formed by chemical and nuclear explosives, terrestrial maars and other volcanic craters, and terrestrial meteorite impact craters, authenticated and probable, were analyzed in the first data set in terms of their mean rim crest diameter, mean interior relief, rim height, and mean exterior rim width. The second data set contained an additional 91 terrestrial craters of which 19 were of experimental percussive impact and 28 of volcanic collapse origin, and which was analyzed in terms of mean rim crest diameter, mean interior relief, and rim height. Principal component analyses were performed on the six genetic types of craters. Ninety per cent of the variation in the variables can be accounted for by two components. Ninety-nine per cent of the variation in the craters formed by chemical and nuclear explosives is explained by the first component alone.

Siegal, B. S.↗
NASA NTRS1974

On the age of the Onverwacht Group, Swaziland sequence, South Africa

Some rocks of the Onverwacht Group, South Africa, have been analyzed for Rb and Sr concentrations and Sr isotopic composition. These rocks include volcanic rocks, layered ultramafic differentiates and cherty sediments. Whole rock data indicate that the Rb-Sr isotopic systems in many samples were open and yield no reasonable isochron relationships. However, the data of mineral separates from a basaltic komatiite define a good isochron of 3.50 (plus or minus .2) b.y. with an initial Sr-87/Sr-86 ratio of 0.70048 plus or minus 5. The orthodox interpretation of this age is the time of the low grade metamorphism. It is reasonable to assume that the age of 3.50 b.y. might also represent the time of initial Onverwacht volcanism and deposition. The initial Sr-87/Sr-86 ratio obtained above is important to an understanding of the Sr isotopic composition of the Archean upper mantle.

Jahn, B.-M.↗
NASA NTRS1974

Pyramidal structures on Mars

Triangular and polygonal pyramid like structures have been observed on the Martian surface. Located in the east central portion of Elysium Quadrangle (MC-15), these features are visible on the Mariner 9 photographs. B frames MTVS 4205-3 DAS 07794853 and MTVS 4296-24 DAS 12985882. The structures cast triangular and polygonal shadows. Steep-sided volcanic cones and impact craters occur only a few kilometers away. The mean diameter of the triangular pyramidal structures at the base is approximately 3.0 km, and the mean diameter of the polygonal structures is approximately 6.0 km. The observed Martian structures tend to line up suggesting joint or fault control. However, they do not appear to be controlled by the visible faults. The structures appear to be either wind-faceted volcanic cones and blocks or solidified blocks which have been rotated in semiconsolidated lava.

Gipson, M., Jr.↗
NASA NTRS1973

Surface configuration as an explanation for lithology-related cross-polarized radar image anomalies

One problem that has persisted since the development of multipolarized radar is the cause or causes of differential depolarization which is expressed as tonal reversals between like- and cross-polarized images of certain outcrops. Rocks producing anomalously low returns on the cross-polarized image could be classed into three general types: (1) certain geologically recent lava flows (late Pleistocene and Holocene), (2) some tertiary volcanics and (3) certain massive sandstones. Differential depolarization has been produced by volcanic rocks of various compositions including rhyolite, rhyodacite, dacite, andesite, and basalt. This has led to the conclusion that differential depolarization is not directly caused by any compositional factor. However, the study of aerial photos and subsequent field observation have led to the conclusion that the weathering and other surface characteristics of the outcrops are responsible for their appearance on multipolarized imagery.

Mccauley, J. R.↗