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At least 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Martian cratering V - Toward an empirical Martian chronology, and its implications

This paper estimates ages of Martian features by dividing least-square-fitted crater densities by an estimated Martian crater production rate. This method is more rigorous than methods based purely on assumptions about correspondence of lunar and Martian cratering rates. Results are interpreted as supporting the conclusion of Burns et al (in press) that Mars shifted climatic states due to a change in obliguity caused by buildup of massive volcanics. Prior to a few gy. ago, conditions favored erosion, deposition, and fluvial channel formation. Recent volcanics postdate this era, and the surfaces of the major shields are fairly well constrained in age to a few hundred my, in agreement with Masursky et al.

Hartmann, W. K.↗
NASA NTRS1977

Pre-Imbrian history of the Fra Mauro region and Apollo 14 sample provenance

Pre-Imbrian impact structures in a large area surrounding the Apollo 14 site were identified in a study of the pre-Imbrian history of the Fra Mauro region. Calculations suggest that a total ejecta thickness of over 1700 m could have accumulated during Phase I (time prior to the Imbrium event) in the area of the ridge on which the Cone crater later formed. The majority (53%) of the ejecta at the site just prior to the Imbrium event was contributed by the numerous large Phase IB and IC craters in the vicinity and not by the lunar basins. Evidence exists for extensive pre-Imbrian volcanic activity in the Fra Mauro region. Early KREEP volcanic deposits may have existed in the target sites of many Phase IB and IC craters and would have been incorporated into their ejecta.

Hawke, B. R.↗
NASA NTRS1979

Application of a coupled aerosol formation: Radiative transfer model to climatic studies of aerosols

A sophisticated one dimensional physical-chemical model of the formation and evolution of stratospheric aerosols was used to predict the size and number concentration of the stratospheric aerosols as functions of time and altitude following: a large volcanic eruption; increased addition of carbonyl sulfide (OCS) or sulfur dioxide (SO2) to the troposphere; increased supersonic aircraft (SST) flights in the stratosphere; and, large numbers of space shuttle (SS) flights through the stratosphere. A radiative-convective one dimensional climate sensitivity study, using the results of the aerosol formation model, was performed to assess the ground level climatic significance of these perturbations to the stratospheric aerosol layer. Volcanic eruptions and large OCS or SO2 increases could cause significant climatic changes. Currently projected SS launches and moderate fleets of SST's are unlikely to upset the stratospheric aerosol layer enough to significantly impact climate.

Toon, O. B.↗
NASA NTRS1978

Imaging radar observations of Askja Caldera, Iceland

A 'blind' test involving interpretation of computer-enhanced like- and cross-polarized radar images is used to evaluate the surface roughness of Askja Caldera, a large volcanic complex in central Iceland. The 'blind' test differs from earlier analyses of radar observations in that computer-processes images and both qualitative and quantitative analyses are used. Attention is given to photogeologic examination and subsequent survey-type field observations, along with aerial photography during the field trip. The results indicate that the 'blind' test of radar interpretation of the Askja volcanic area can be considered suitable within the framework of limitations of radar data considered explicitly from the onset. The limitations of the radar techniques can be eliminated by using oblique-viewing conditions to remove geometric distortions and slope effects.

Malin, M. C.↗
NASA NTRS1978

Stratospheric aerosols and climatic change

Stratospht1ic sulfuric acid particles scatter and absorb sunlight and they scatter, absorb and emit terrestrial thermal radiation. These interactions play a role in the earth's radiation balance and therefore affect climate. The stratospheric aerosols are perturbed by volcanic injection of SO2 and ash, by aircraft injection of SO2, by rocket exhaust of Al2O3 and by tropospheric mixing of particles and pollutant SO2 and COS. In order to assess the effects of these perturbations on climate, the effects of the aerosols on the radiation balance must be understood and in order to understand the radiation effects the properties of the aerosols must be known. The discussion covers the aerosols' effect on the radiation balance. It is shown that the aerosol size distribution controls whether the aerosols will tend to warm or cool the earth's surface. Calculations of aerosol properties, including size distribution, for various perturbation sources are carried out on the basis of an aerosol model. Calculations are also presented of the climatic impact of perturbed aerosols due to volcanic eruptions and Space Shuttle flights.

Toon, O. B.↗
NASA NTRS1978

Floor-fractured craters on the moon and Mars

Impact craters on the moon provided primary pathways for volcanic eruptions through shock-induced fractures that immediately or subsequently tap magma reservoirs. Evidence for this process includes unbreached lava-filled craters and fractured crater floors with associated eruptives. Over 200 craters with floor fractures have been identified on the moon. They commonly occur along the margins of irregular maria, thereby suggesting a link to this important phase of lunar volcanism. Topographic data reveal small elevation differences between the summit of the remnant central peaks and crater rim, and in many cases suggest that floor fracturing resulted from a tabular intrusion localized beneath the crater with uplift of the crater floor. A comparison of lunar and Martian crater photographs shows that some Martian craters also exhibit similar highly localized endogenic modifications.

Schultz, P. H.↗
NASA NTRS1979

Tharsis Province of Mars - Geologic sequence, geometry, and a deformation mechanism

Tharsis development apparently involved two stages: (1) an initial rapid topographic rise accompanied by the development of a vast radial fault system and (2) an extremely long-lived volcanic stage apparently continuing to the geological present. A deformation model is proposed in which a first-order mantle convection cell caused early subcrustal erosion and foundering of the low third of the planet. Underplating and deep intrusion by the eroded materials beneath Tharsis caused isostatic doming. Minor radial gravity motions of surficial layers off the dome produced the radial fault system. The hot underplate eventually affected the surface to cause the very long-lived volcanic second stage.

Wise, D. U.↗
NASA NTRS1979

Venus - Preliminary topographic and surface imaging results from the Pioneer Orbiter

Three large Venus surface features, identified previously in images obtained from earth-based radar observations, are shown by the Pioneer Venus radar mapper to be elevated 5 to 10 km above the surrounding terrain. Two of these features, one bright and the other dark, lie adjacent to each other astride the 65 N parallel between longitudes 310 E and 10 E. The combined region forms a huge tectonically uplifted plateau, surmounted by radar-bright ridges that may have either a volcanic or tectonic origin. The third feature, located at 30 N, 283 E, is radar-bright and may consist of volcanic material extruded along a fault zone. A first radar-scattering image, compiled from data obtained by the mapper in its imaging mode, shows a region north of the equator; several circular depressions seen in this area may result from meteoritic impact.

Pettengill, G. H.↗
NASA NTRS1979

Preliminary geological mapping of Io

A preliminary summary of information gained by Voyager 1 on the colored, terrain and landform surface units of Io and their global distribution is presented. Colored units are classified as white to bluish-white regions which may be sulfur or sulfur dioxide deposits, red, orange, or yellow regions thought to contain various sublimates or alterations of sulfur, brownish regions limited to the polar areas and dark brown areas surrounding some vents. Terrain features observed include plains broken by scarps, isolated mountainous regions and volcanic vents resembling terrestrial caldera or pit craters. Maps of the distribution of these features, compiled by photogeological mapping techniques developed for terrestrial volcanic mapping, are presented, and the implications of the surface unit distributions for the volcanology, crustal composition, internal convection patterns and surface age of Io are discussed.

Masursky, H.↗
NASA NTRS1979

The stability of an SO2 atmosphere on Io

Active volcanism observed on Io could provide a continuous source of gases from Io's interior. Only a small fraction of what is coming out of Io's volcanoes is escaping; the bulk of it is being recycled. There must be an atmospheric reservoir which maintains the gases until they have had a chance to recycle. Such an atmosphere must be protected from Jupiter's corotating plasma in order to be stable. Only the dayside atmosphere is subject to escape, while the cold nightside and poles would serve as a sink for atmospheric gases. However, the scavenging of atmospheric gases is maximum at the eastern elongation and minimum at the western elongation. A stable SO2 atmosphere on Io shows promise if the volcanic activity is continuous. If the volcanoes stop erupting, the atmosphere will be depleted.

Kumar, S.↗
NASA NTRS1980

Research on lunar Mare emplacement and impact cratering experiments

A model was derived enabling the interpretation of lunar styles of volcanism through the analysis of various surface features. The model was applied to several areas on the Moon, including the Orientale Basin, the Smythii Basin, the Herigonious region, and several highland areas. Concurrent with the application of the model, several topical studies of various aspects of lunar volcanism were completed. A series of impact crater experiments was conducted at NASA Ames in order to determine the effect that viscous targets would have on cratering mechanics and morphology for application in studies of Martian ejecta flow craters. The results of the experiments led to a model that can account for the formation of multiple flow lobes and the general morphology of some aspects of Martian craters.

Greeley, R.↗
NASA NTRS1979

Lunar and Planetary Science Conference, 10th, Houston, Tex., March 19-23, 1979, Proceedings. Volume 3 - Planetary interiors and surfaces

The areas covered on the present symposium include geophysical investigations based on laboratory and planetary measurements; impact and volcanic processes; and planetary surface features and processes. The topics discussed include models of an early lunar dynamo, parameterized convection within the moon and the terrestrial planets, the bounds of the heat production rate with the moon, the shock metamorphism of granulated lunar basalt, asymmetric terracing of lunar highland craters, large impact basins on Mercury, impact melting in early lunar history, and evidence for ancient mare volcanism.

Merrill, R. B.↗
NASA NTRS1979

Pseudocraters on Mars

In the Cydonia region of southern Acidalium Planitia are small, low-relief, apparently volcanic domelike structures, whose size, morphology, and general occurrence suggest they are martian analogs of terrestrial pseudocraters, a type of phreatic eruption. Average base diameters are about 800 m, which is somewhat larger than typical Icelandic examples. All the domes have summit pits; elongate domes generally have elongate summit pits or, in extreme cases, double pits. The greatest concentration of these domes is in a region of subdued fractured plains which may be old volcanic flows. Pseudocraters on the earth are produced when lava flows over water-logged ground. On Mars surface or subsurface ice was the likley medium that produced the steam eruptions resulting in cratered domelike structures on the lava surfaces.

Frey, H.↗
NASA NTRS1980

Infrared spectrum of Io, 2.8-5.2 microns

The reflectance spectrum of Io is presented from 2.8 to 5.2 microns demonstrating the full extent of the broad and deep spectral absorption between 3.5 and 4.8 microns. Laboratory spectra of nitrates and carbonates diluted with sulfur do not satisfactorily reproduce the Io spectrum, but new information based on recently discovered volcanic activity on the satellite lead to consideration of other classes of compounds reported by Fanale et al. (1979). It is concluded that the variability of the supply of condensible SO2 gas to the surface of Io, its removal by sublimination, and the temporal variations in the strength of the SO2 band may provide an index of volcanic activity on Io that can be monitored from the earth.

Cruikshank, D. P.↗
NASA NTRS1980

Iron and titanium distribution on the moon from orbital gamma ray spectrometry with implications for crustal evolutionary models

A set of Fe and Ti maps and regional values are obtained from the Apollo 15 and 16 orbital gamma ray data by energy band analysis. High-Ti basalts predominate the early and late stages of mare volcanism with high-Fe basaltic volcanism in the interim. The first evidence of a high-Ti-KREEP basalt association is found in the Aristarchus region. A N-S asymmetry for Fe and Ti in the east limb and farside highlands complicates the E-W asymmetry for Th but substantiates crustal inhomogeneity. The observed crustal inhomogeneity adds an additional objection to the primitive source model for crustal evolution. The high-Ti-KREEP basalt association and the general trend of decreasing mare basalt Ti with time lend support to the cumulate source model; however, this model cannot account for young, high-Ti maria. The dynamic assimilation model better accounts for chemical variations observed on the moon.

Davis, P. A., Jr.↗
NASA NTRS1980

Radar, visual and thermal characteristics of Mars - Rough planar surfaces

High-resolution Viking Orbiter images contain significant information on Martian surface roughness at 25- to 100-m lateral scales, while earth-based radar observations of Mars are sensitive to roughness at lateral scales of 1 to 30 m or more. High-rms slopes predicted for the Tharsis-Memnonia-Amazonis volcanic plains from extremely weak radar returns are qualitatively confirmed by the Viking image data. Large-scale, curvilinear ridges on lava flows in the Memnonia Fossae region are interpreted as innate flow morphology caused by compressional foldover of moving lava sheets of possible rhyolite-dacite composition. The presence or absence of a recent mantle of fine-grained eolian material on the volcanic surfaces studied was determined by the visibility of fresh impact craters with diameters less than 50 m. Lava flows with surfaces modified by eolian erosion and deposition occur west-northwest of Apollinaris Patera at the border of the cratered equatorial uplands and southern Elysium Planitia. Nearby yardangs, for which radar observations indicate very high-rms slopes, are similar to terrestrial features of similar origin.

Schaber, G. G.↗
NASA NTRS1979

Photogeological constraints on lunar and planetary vulcanism, part 1

Central volcanic constructs were studied as constraints on the thermal evolution and regional tectonics of the Moon and terrestrial planets. The origins of sub-kilometer lunar craters were examined with regards to implications for mare basalt petrogenesis. The morphology, distribution, age, and tectonic setting of the volcanic constructs were studied using Viking Orbiter data.

Source record↗
NASA NTRS1981

A global tectonic activity map with orbital photographic supplement

A three part map showing equatorial and polar regions was compiled showing tectonic and volcanic activity of the past one million years, including the present. Features shown include actively spreading ridges, spreading rates, major active faults, subduction zones, well defined plates, and volcanic areas active within the past one million years. Activity within this period was inferred from seismicity (instrumental and historic), physiography, and published literature. The tectonic activity map was used for planning global geodetic programs of satellite laser ranging and very long base line interferometry and for geologic education.

Lowman, P. D., Jr.↗