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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Identification, distribution and significance of lunar volcanic domes.

Over 300 previously unrecognized volcanic domes were identified on Lunar Orbiter photographs using the following criteria: (1) the recognition of land forms on the Moon similar in morphology to terrestrial volcanic domes, (2) structural control, (3) geomorphic discordance, and (4) the recognition of land forms modified by dome-like swellings. Many terrestrial volcanic domes are similar in morphology to lunar domes. This analogy suggests that some lunar hills are in fact extrusive volcanic domes. Many of the domes identified in this paper seem to be related to basins and craters, and with the exception of local tectonic grid control few domes are related to any observable Moon-wide pattern.

Smith, E. I.↗
NASA NTRS1973

Application of ERTS imagery to geologic mapping in the volcanic terrane of northwest Wyoming

The author has identified the following significant results. ERTS-1 image interpretations in the Yellowstone/Absaroka volcanic province indicate that the ERTS-1 imagery can be successfully employed in mapping large-scale structures and gross lithologic differences within the volcanic rocks. The volcanic rocks are readily separable from the sedimentary and crystalline rocks but the various volcanic units are seldom distinguishable unless they exhibit a characteristic morphology. Color anomalies were detected on the ERTS-1 imagery and found to be related to zones of alteration and mineralization. High altitude aircraft imagery provided a means of checking and improving the interpretations.

Breckenridge, R. M.↗
NASA NTRS1974

Synopsis of volcanic stratigraphy

Volcanic stratigraphic units are mappable layered units composed of volcanic rocks that are formed on land (subaerially) or under water (subaqueously) by volcanic processes. At least ten different types of volcanic stratigraphic units are recognized. The characteristics for each are discussed briefly and some typical examples are illustrated by diagrams to show their salient features.

Hammond, P. E.↗
NASA NTRS1976

Mercurian volcanism questioned

It is noted that reports of the Mariner 10 television team favor a volcanic origin for the plains materials on Mercury. The present paper advances the argument that the Mercurian plains more closely resemble the lunar light plains (which are not of volcanic origin) in terms of stratigraphic relations, surface morphology, and albedo contrast. It is suggested that the plains on Mercury may have been formed from impact materials, possibly impact melts or other basin ejecta which behaved more like a fluid than did the lunar ejecta. It is concluded that if the old intercrater plains and younger smooth plains of Mercury were formed from impact materials, then Mercury underwent neither the volcanic interlude between early cratering episodes nor the late mare-type volcanic phase deduced by the Mariner 10 investigators.

Wilhelms, D. E.↗
NASA NTRS1977

Similarity laws of lunar and terrestrial volcanic flows

A mathematical model of a one dimensional, steady duct flow of a mixture of a gas and small solid particles (rock) was analyzed and applied to the lunar and the terrestrial volcanic flows under geometrically and dynamically similar conditions. Numerical results for the equilibrium two phase flows of lunar and terrestrial volcanoes under similar conditions are presented. The study indicates that: (1) the lunar crater is much larger than the corresponding terrestrial crater; (2) the exit velocity from the lunar volcanic flow may be higher than the lunar escape velocity but the exit velocity of terrestrial volcanic flow is much less than that of the lunar case; and (3) the thermal effects on the lunar volcanic flow are much larger than those of the terrestrial case.

Pai, S. I.↗
NASA NTRS1985

Volcanic Debris Flows in the Elysium Region of Mars

Photogeologic studies of the Elysium volcanic province appear to provide a specific example of the importance of volcanic-ice interaction to produce the channels of Hrad and Granicus Valles. In addition, these studies shows that the channels lie on the surface of a large sedimentary deposit which is interpreted as an accumulation of volcanic debris flows or lahars. In spite of some similarities with Martian outflow channels, this latter difference may distinguish the Elysium channels from other types of Martian channels. Geologic relations are described which demonstrate that the debris flows formed amidst other volcanic activity in the Elysium region thereby suggesting that the magmatism was important to the generation of the mobilizing liquid. The lahars resulted from the melting of ground ice and liquefaction of subsurface materials. The intersection of this fluid reservoir with the regional fracture system lead to the rapid expulsion of a muddy slurry down the steep western slope of the province.

Christiansen, E. H.↗
NASA NTRS1984

Volcanic hotspots on Io - Stability and longitudinal distribution

The first results of a program to determine the longitudinal distribution of volcanic activity on Jupiter's satellite Io are presented. Infrared measurements at 8.7, 10, and 20 micrometers have been taken at a variety of orbital longitudes: strong variation in the 8.7- and 10-micrometer flux with longitude demonstrates that infrared emission arising from volcanic hotspots on Io is strongly concentrated in a few locations. Analysis of these data suggests that the active volcanic regions observed by the Voyager experimenters are still active, particularly the region around the feature known as Loki. Another source of flux, although of somewhat smaller magnitude, is indicated on the opposite hemisphere. If these sources are the only major volcanic centers on Io, then current global heat flow estimates must be revised downward. However, heat flow from as yet unobserved longitudes, hotspots at high latitudes, and conducted heat flow must still be measured.

Johnson, T. V.↗
NASA NTRS1984

Venus - Volcanism and rift formation in Beta Regio

A new high-resolution radar image of Beta Regio, a Venus highland area, confirms the presence of a major tectonic rift system and associated volcanic activity. The lack of identifiable impact craters, together with the apparent superposition of the Theia Mons volcanic structure on the rift system, suggest that at least some of the volcanic activity occurred in relatively recent geologic time. The presence of topographically similar highland areas elsewhere on Venus (Aphrodite Terra, Dali Chasma, and Diana Chasma) suggests that rifting and volcanism are significant processes on Venus.

Campbell, D. B.↗
NASA NTRS1985

Similarities and contrasts in tectonic and volcanic style and history along the Colorado plateaus-to-basin and range transition zone in Western Arizona: Geologic framework for tertiary extensional tectonics

The overall temporal and spatial relations between middle Tertiary volcanism and tectonism from the Basin and Range province onto the edge of the Colorado Plateaus province suggest that a single magnetic-tectonic episode affected the entire region more or less simultaneously during this period. The episode followed a post-Laramide (late Eocene through Oligocene) period of 25 million years of relative stability. Middle Tertiary volcanism did not migrate gradually eastward in a simple fashion onto the Colorado Plateau. In fact, late Oligocene volcanism appears to be more voluminous near the Aquarius Mountains than throughout the adjacent Basin and Range province westward to the Colorado River. Any model proposed to explain the cause of extension and detachment faulting in the eastern part of the Basin and Range province must consider that the onset of volcanism appears to have been approximately synchronous from the Colorado River region of the Basin and Range across the transition zone and onto the edge of the Colorado Plateaus.

Young, R. A.↗
NASA NTRS1986

Silicate volcanism on Io

This paper is mainly concerned with the nature of volcanic eruptions on Io, taking into account questions regarding the presence of silicates or sulfur as principal component. Attention is given to the generation of silicate magma, the viscous dissipation in the melt zone, thermal anomalies at eruption sites, and Ionian volcanism. According to the information available about Io, it appears that its volcanism and hence its surface materials are dominantly silicic. Several percent of volatile materials such as sulfur, but also including sodium- and potassium-rich materials, may also be present. The volatile materials at the surface are continually vaporized and melted as a result of the high rates of silicate volcanism.

Carr, M. H.↗
NASA NTRS1988

NASA MEVTV Program Working Group Meeting: Volcanism on Mars

The purpose of this working group meeting is to focus predominantly on volcanism on Mars, prior to considering the more complex issues of interactions between volcanism and tectonism or between volcanism and global or regional volatile evolution. It is also hoped that the topical areas of research identified will aid the planetary geology community in understanding volcanism on Mars and its relationship to other physical processes.

Source record↗
NASA NTRS1988

The Martian highland paterae: Evidence for explosive volcanism on Mars

The Martian surface exhibits numerous volcanic landforms displaying great diversity in size, age, and morphology. Most research regarding Martian volcanology has centered around effusive basaltic volcanism, including analyses of individual lava flows, extensive lava plains, and large shield volcanoes. These studies were hindered by a lack of definitive morphologic criteria for the remote identification of ash deposits. Knowledge of the abundances, ages, and geologic settings of explosive volcanic deposits on Mars is essential to a comprehensive understanding of the evolution of the Martian surface, with implications for the evolution of the lithosphere and atmosphere as well as the histories of specific volcanic centers and provinces.

Crown, David A.↗
NASA NTRS1988

Volcanism, global catastrophe and mass mortality

The effects of very large volcanic eruptions are well documented in many studies, mostly based on observations made on three historic eruptions, Laki 1783; Tambora 1815 and Krakatau 1883. Such eruptions have effects that are catastrophic locally and measurable globally, but it is not clear that even the largest volcanic eruptions have had global catastrophic effects, nor caused mass extinctions. Two different types of volcanic eruption were considered as likely to have the most serious widespread effects: large silicic explosive eruptions producing hundreds or thousands of cubic kilometers of pyroclastic materials, and effusive basaltic eruptions producing of approximately 100 cubic kilometers of lava. In both cases, the global effects are climatic, and attributable to production of stratospheric aerosols. Other possibilities need to be explored. Recent research on global change has emphasized the extreme sensitivity of the links between oceanic circulation, atmospheric circulation and climate. In particular, it was argued that the pattern of ocean current circulation (which strongly influences climate) is unstable; it may rapidly flip from one pattern to a different one, with global climatic consequences. If volcanism has been a factor in global environmental change and a cause of mass extinctions, it seems most likely that it has done so by providing a trigger to other processes, for example by driving oceanic circulation from one mode to another.

Francis, P. W.↗
NASA NTRS1989

Estimation of the rate of volcanism on Venus from reaction rate measurements

Laboratory rate data for the reaction between SO2 and calcite to form anhydrite are presented. If this reaction rate represents the SO2 reaction rate on Venus, then all SO2 in the Venusian atmosphere will disappear in 1.9 Myr unless volcanism replenishes the lost SO2. The required volcanism rate, which depends on the sulfur content of the erupted material, is in the range 0.4-11 cu km of magma erupted per year. The Venus surface composition at the Venera 13, 14, and Vega 2 landing sites implies a volcanism rate of about 1 cu km/yr. This geochemically estimated rate can be used to determine if either (or neither) of two discordant geophysically estimated rates is correct. It also suggests that Venus may be less volcanically active than the earth.

Fegley, Bruce, Jr.↗
NASA NTRS1989

Self-limiting physical and chemical effects in volcanic eruption clouds

One-dimensional aerosol microphysical and photochemical models are used to study the chemistry of stratospheric volcanic clouds. The results indicate that the aerosol microphysical processes of condensation and coagulation produce larger particles as the SO2 injection rate is increased. Larger particles have a smaller optical depth per unit mass and settle out of the stratosphere at a faster rate than smaller ones, restricting the total number of particles in the stratosphere. The microphysical processes moderate the impact of volcanic clouds on the earth's radiation budget and climate, suggesting that volcanic effects may be self limiting. It is noted that the injection of HCl into the stratosphere, which could lead to large ozone changes, is limited by a cold trap effect in which HCl and water vapor condense on ash particles in the rising volcanic plume and fall out as ice.

Pinto, Joseph P.↗
NASA NTRS1989

Tectonics and volcanism in central Mexico - A Landsat Thematic Mapper perspective

Digitally enhanced Landsat Thematic Mapper (TM) images were used to map neotectonic deformation in central Mexico. This region has been studied for decades using a variety of geological and geophysical techniques, but synoptic mapping of neotectonic activity and major fault zones there, and an evaluation of their regional relationship to the character and location of volcanism were not previously possible until the application of synoptic, high resolution satellite imagery. Interpretation of the TM images shows that the tectonic deformation is closely linked in time and space to the dominantly calc-alkaline volcanics of the Mexican Volcanic Belt (MVB). The eruptive style and distribution of the volcanics is clearly related to the deformation resulting from relative motions of three large crustal blocks south of the MVB. Therefore, zones of weakness within the crust of central Mexico, which may be inherited from earlier episodes of deformation, are a principal factor controlling the oblique orientation of the MVB relative to the Acapulco Trench.

Johnson, C. A.↗
NASA NTRS1990

Young volcanic deposits in the Valles Marineris, Mars?

The emplacement of a sequence of deposits covering the chasma floors of the central Valles Marineris of Mars, ranging from thin dust to several km in thickness, appears to have been the last major formational event. These deposits fall into the categories of (1) dark patches lying along faults, (2) light-colored deposits locally associated with craters, and (3) mottled, rugged deposits. It is presently suggested that these materials may be of volcanic origin, in view of their low albedo, their association with faults and possible volcanic features, and their embayment relations and lobate margins. If the suggestion is true, then the occasionally explosive volcanism in question was associated with rifting in the Valles Marineris, and may be as young as the late Tharsis volcanism.

Lucchitta, B. K.↗
NASA NTRS1991

Historical evidence for a connection between volcanic eruptions and climate change

The times of historical volcanic aerosol clouds were compared with changes in atmospheric temperatures on regional, hemispheric, and global scales. These involve either a direct comparison of individual significant eruption years with temperature records, or a comparison of eruption years with composited temperature records for several years before and after chosen sets of eruptions. Some studies have challenged the connection between individual eruptions and climate change. Mass and Portman (1989) recently suggested that the volcanic signal was present, but smaller than previously thought. In a study designed to test the idea that eruptions could cause small changes in climate, Hansen and other (1978) chose one of the best monitored eruptions at the time, the 1963 eruption of Agung volcano on the island of Bali. Using a simple radiation-balance model, in which an aerosol cloud in the tropics was simulated, this basic pattern of temperature change in the tropics and subtropics was reproduced. There may be natural limits to the atmospheric effects of any volcanic eruption. Self-limiting physical and chemical effects in eruption clouds were proposed. Model results suggest that aerosol microphysical processes of condensation and coagulation produce larger aerosols as the SO2 injection rate is increased. The key to discovering the greatest effects of volcanoes on short-term climate may be to concentrate on regional temperatures where the effects of volcanic aerosol clouds can be amplified by perturbed atmospheric circulation patterns, especially changes in mid-latitudes where meridional circulation patterns may develop. Such climatic perturbations can be detected in proxy evidence such as decreases in tree-ring widths and frost damage rings in climatically sensitive parts of the world, changes in treelines, weather anomalies such as unusually cold summers, severity of sea-ice in polar and subpolar regions, and poor grain yields and crop failures.

Rampino, Michael R.↗