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NASA NTRS2004

Deflections in Lava Flow Directions Relative to Topography in the Tharsis Region of Mars: Indications of Post-Flow Tectonic Motion

High-resolution topographic data from the Mars Orbiter Laser Altimeter (MOLA), and imagery from the Mars Orbiter Camera (MOC) and the Thermal Emission Imaging System (THEMIS) allow for the first accurate assessment of lava flow directions relative to topographic slopes in the Tharsis region. Tharisis has long been recognized as the dominant tectonic and volcanic province on the planet, with a complex geologic history. In this study, lava flow directions on Daedalia Planum, Syria Planum, Tempe Terra, and near the Tharsis Montes are compared with MOLA topographic contours to look for deviations of flow directions from the local slope direction. The topographic deviations identified in this study are likely due to Tharsis tectonic deformation that has modified the regional topography subsequent to the emplacement of the flows, and can be used to model the mechanisms and magnitudes of relatively recent tectonism in the region. A similar approach was used to identify possible post-flow tectonic subsidence on the Snake River Plain in Idaho.

Chadwick, D. J.↗

NASA NTRS1993

Numerical simulation of lava flows: Applications to the terrestrial planets

Lava flows are the visible expression of the extrusion of volcanic materials on a variety of planetary surfaces. A computer program described by Ishihara et al. appears to be well suited for application to different environments, and we have undertaken tests to evaluate their approach. Our results are somewhat mixed; the program does reproduce reasonable lava flow behavior in many situations, but we have encountered some conditions common to planetary environments for which the current program is inadequate. Here we present our initial efforts to identify the 'parameter space' for reasonable numerical simulations of lava flows.

Zimbelman, James R.↗

NASA NTRS1992

Joints in Venusian lava flows

The bright polygonal patterns seen in some Magellan images of the volcanic plains are interpreted as joint networks. Several areas displaying such patterns are identified, noting their areal extent, the presence of volcanic features, and the regional topography. Intersection geometries of the lineations defining the polygonal patterns are typical of those found in tensile networks. In addition, the polygonal patterns exhibit no preferred orientation, implying that they are the result of horizontally isotropic stress fields. It is demonstrated that sufficient tensile stresses develop in a cooling Venusian flow to allow joints to form and that the thermal strain predicted is not incompatible with that observed. It is suggested that the tensioned networks are the result of a thermally stressed layer much thicker than a single lava flow. A second model is also considered in which thermal stresses develop as a result of regional elevation of the temperature gradient.

Johnson, Catherine L.↗

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 NTRS1971

Lava tubes and channels in the Lunar Marius Hills.

The Marius Hills region, a volcanic plateau in Oceanus Procellarum, contains numerous rilles, rille-like structures, and chains of elongate craters. Most of these structures characteristically: (1) originate on or near irregular shaped craters associated with features previously interpreted as volcanic domes, (2) trend downslope onto Plateau Plains, (3) generally taper in width and become shallower, (4) are often discontinuous, (5) occupy the center, or apparent crest of a broad ridge, (6) may contain cut-off branches and distributary structures, and (7) may have local reversals in longitudinal slope. Structures having these characteristics are interpreted to be lava channels or partly collapsed lava tubes. Terrestrial lava tubes form exclusively, and commonly, in fluid basalt flows. Recent evidence indicates that viscosities of lunar mare 'basalt' lava flows were conducive for lava tube formation. Terrestrial analogs are offered for structures described in the Marius Hills.

Greeley, R.↗

NASA NTRS1989

A quad-pol radar scattering model for use in remote sensing of lava flow morphology

Mapping of spatial variations in surface roughness over large regions is required to understand the nature of volcanic terrains. An invertible scattering model for quad-polarization radar data is presented to assist in the remote-sensing analysis of lava flow surface morphology. This model permits separation of the polarized part of the radar echo into quasispecular, dihedral, and small-perturbation scatterin components, based on an assumed surface dielectric constant. Tests are presented for a quad-pol scene of Craters of the Moon National Monument in Idaho, where there are a number of basaltic lava flows of differing surface morphology. Comparison of calculated model components with the observed morphology of the lava flows suggests that this technique may be useful for the remote description of changes in surface roughness. The scattering mechanisms chosen to represent the polarizing behavior of the real surface display correlations which indicate that they are sensitive to the expected scales of roughness.

Campbell, Bruce A.↗

NASA NTRS2011

Carbonate Cements from the Sverrefjell and Sigurdfjell Volcanoes, Svalbard Norway: Analogs for Martian Carbonates

The Sverrefjell and Sigurdfjell volcanic complexes erupted at ~1Ma on Svalbard, Norway. Sverrefjell is a cone of cinders, pillow lavas and dikes; Sigurdfjell is elongate in outcrop and may represent a fissure eruption [1]. The lavas of both volcanos were volatile rich. The volcanos erupted under ice and were subsequently dissected by glaciation (glacial eratics are present on most of Sverrefjell, even on its summit). Eruption beneath an ice sheet is inferred, based on the presence of pillow lavas from near sea level to ~1000 m above sea level. Sverrefjell contains the largest fraction of ultramafic xenoliths of any volcanic complex in the world, in places accounting for as much as 50% of the volume of the outcrop. The Sverrefjell and Sigurdfell volcanos contain carbonate cements of several varieties: (1) Amundsen [2] reported Mg-Fe-rich carbonate in sub-mm globules in basalts and ultramafic xenoliths from the volcanos. These globules are the best terrestrial analogs to the carbonate globules in the Mars meteorite ALH84001 [3]. (2) Thick (1-3 cm) coatings of carbonate cement drape the walls of vertical volcanic pipes or conduits on the flanks and near the present summit of Sverrefjell. Similar occurrences are found on Sigurdfjell. (3) Breccia-filled pipes or vents occur on Sverrefjell and Siggurdfjell in which the breccia fragments are cemented by carbonate. The fragments themselves commonly contain carbonate globules similar to those found in the basalts and ultramafic xenoliths.

Blake, D. F.↗

NASA NTRS1976

Floor-fractured lunar craters

Observational data concerning floor-fractured craters on the lunar near and far sides are examined, including the morphologic classification of the craters, their spatial and size distributions, and their floor, peak, and rim elevations relative to the maria. Six morphologic classes and two subclasses are delineated on the basis of fracture pattern, crater floor depth, and floor type. These data are used to reconstruct a history of crater modification which accounts for the large differences in affected crater size and age, the small peak-rim elevation differences, remnant central peaks within mare-flooded craters and ringed plains, ridged and flat-topped rim profiles of heavily modified craters and ringed plains, as well as the absence of positive gravity anomalies in most floor-fractured craters and some large mare-filled craters. The results indicate that: (1) impact craters became centers of intrusions and volcanism generally related to periods of basin inundation by mare basalts; (2) some light-plains units in the highlands may be due to both impact ejecta and extrusions of light-colored lava or ash; (3) floor-fractured craters may have become important volcanic vents that contributed to the inundation of the lunar surface by mare basalts; and (4) the lunar highlands probably did not fully escape the epochs of mare flooding.

Schultz, P. H.↗

NASA NTRS1988

Catastrophic volcanism

Since primitive times, catastrophes due to volcanic activity have been vivid in the mind of man, who knew that his activities in many parts of the world were threatened by lava flows, mudflows, and ash falls. Within the present century, increasingly complex interactions between volcanism and the environment, on scales not previously experienced historically, have been detected or suspected from geologic observations. These include enormous hot pyroclastic flows associated with collapse at source calderas and fed by eruption columns that reached the stratosphere, relations between huge flood basalt eruptions at hotspots and the rifting of continents, devastating laterally-directed volcanic blasts and pyroclastic surges, great volcanic-generated tsunamis, climate modification from volcanic release of ash and sulfur aerosols into the upper atmosphere, modification of ocean circulation by volcanic constructs and attendent climatic implications, global pulsations in intensity of volcanic activity, and perhaps triggering of some intense terrestrial volcanism by planetary impacts. Complex feedback between volcanic activity and additional seemingly unrelated terrestrial processes likely remains unrecognized. Only recently has it become possible to begin to evaluate the degree to which such large-scale volcanic processes may have been important in triggering or modulating the tempo of faunal extinctions and other evolutionary events. In this overview, such processes are examined from the viewpoint of a field volcanologist, rather than as a previous participant in controversies concerning the interrelations between extinctions, impacts, and volcanism.

Lipman, Peter W.↗

NASA NTRS1980

Estimation of the thickness of the Tharsis lava flows and implications for the nature of the topography of the Tharsis plateau

An attempt to estimate the thickness of the volcanics which cover the large part of the Tharsis region is reported. Estimates for the thickness of the flows were made using the numerous occurrences of the partially buried craters throughout the region and a relation between the crater diameter and crater rim height. Estimates were made along the southern contact with the heavily cratered terrain in the Phoenicis Lacus and Memnonia quadrangles, and along the northeast contact with older plains units in the Tharsis and Lunae Palus quadrangles. In these distal regions the thickness estimates range from 0 to 600-700 m of lava. This would indicate that only 20-30% of the topography is the result of volcanic construction. If the 20-30% estimate is representative of Tharsis as a whole then lava thickness would reach only 2-3 km near the center of the region. Thus only a small fraction of the topography presently observed can be attributed to units readily identifiable as volcanic. This additional evidence indicates that the model for Tharsis of a pre-existing elevated region of heavily cratered crust, capped by a veneer of volcanics is correct.

Plescia, J. B.↗

NASA NTRS2004

Lava Lakes on Io: New Perspectives from Modeling

Ionian paterae are a class of volcanic feature that are characterized by irregular craters with steep walls, flat floors, and arcuate margins that may or may not exhibit nesting. Loki (310 W, 12 N) is Io's largest patera at approx.200 km in diameter (Figure 1), and may account for 15% of Io's total heat flow. Earth-based infrared data, as well as information collected using the Galileo Near-Infrared Mapping Spectrometer (NIMS) and the Photopolarimeter Radiometer (PPR) have been used to interpret Loki s eruption style. Debate continues over whether Loki s occasional (periodic or not) temperature increases are due to an overturning lava lake within the patera, or to an eruption of surface flows on the patera floor. Interpretation of model results and comparisons with active terrestrial lava lakes suggest that Loki behaves quite differently from active lava lakes on Earth, and that surface flows (rather than an overturning lava lake) are a more likely explanation of Loki's thermal brightening.

Gregg, Tracy K. P.↗

NASA NTRS1972

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

Three rock types are described that produce dark cross-polarized images on Ka-band imagery: lava flows dating from Pleistocene and Holocene, some Tertiary volcanics, and certain massive sandstones. Their planar surfaces are large with respect to the wavelength of the Ka-band system, yet are small in comparison to the resolution. It is found that only outcrops with proper faceted surface orientations produce significant radar returns showing the dominance of specular reflectors. The omnidirectional attitude of the facets and their wide distribution on the outcrops explains the independence of look-direction that the flat-lying anomalous outcrops exhibit in production of darker cross-polarized images.

Mccauley, J. R.↗

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.↗

NASA NTRS1978

The mantle of Mars - Some possible geological implications of its high density

The high density of the Martian mantle probably implies an iron-rich composition expressed by a higher concentration of FeO than that in the earth's mantle. Examination of high-pressure mineralogies suggests that the model Martian mantle has an oxide-garnet wehrlite phase assemblage. This mantle model would be likely to yield ultrabasic (ferrobasaltic) melts of very low viscosity. The prevalence of low-viscosity material is consistent with large eruption rate and copious lava flow on the planet. Furthermore, ferro-kimberlite volcanic ash may be an abundant constituent in the Martian soil, especially if there was much volatile material within the early accreting Mars.

Mcgetchin, T. R.↗

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 NTRS1993

Large volcanoes on Venus: Examples of geologic and structural characteristics from different classes

Large volcanoes characterized by radial lava flows and similar evidence for a topographic edifice are widely distributed over the surface of Venus and geologically diverse. Based on the global identification of more than 165 examples and preliminary geologic mapping, large volcanoes range from those characterized geologically as simple lava edifices to those bearing evidence of complexly developed volcanic and structural histories. Many large volcanoes exhibit characteristics transitional to other large magnetic center types such as coronae and novae. In this study, we examine the geology and structure of several type examples of large volcanoes not addressed in previous studies which are representative of several of the morphological classes.

Crumpler, L. S.↗

NASA NTRS1998

Potential Mars Surveyor 2001 Landing Sites Near Apollinaris Patera

Landing sites near Apollinaris Patera are proposed for the Mars Surveyor 2001 lander/rover mission. Regions near the base of Apollinaris Patera provide a unique opportunity within the proposed -15(beta)o 30(beta) latitude belt to sample outcrop lithologies ranging from highland Noachian basement rocks, to Hesperian aged lava flows, channel and flood plain materials, to Amazonian volcanic, ash flow, and channel deposits. Pristine impact craters exhibiting lobate ejecta blankets are found both on the volcano itself and on the surrounding terrain implying a ground water rich environment well into the Amazonian. Therefore its formation likely induced long-lived volcanic-hydrothermal systems, a high priority target for the mission.

Gulick, Virginia C.↗

NASA NTRS1998

Potential Mars Surveyor 2001 Landing Sites Near Apollinaris Patera

Landing sites near Apollinaris Patera are proposed for the Mars Surveyor 2001 lander/rover mission. Regions near the base of Apollinaris Patera provide a unique opportunity within the proposed -15 deg to 30deg latitude belt to sample outcrop lithologies ranging from highland Noachian basement rocks, to Hesperian aged lava flows, channel and flood plain materials, to Amazonian volcanic, ash flow, and channel deposits. Pristine impact craters exhibiting lobate ejecta blankets are found both on the volcano itself and on the surrounding terrain implying a ground water rich environment well into the Amazonian. Therefore its formation likely induced long-lived volcanic-hydrothermal systems, a high priority target for the mission.

Gulick, Virginia C.↗