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A table for use in identifying Martian land forms that may be volcanic in nature is presented. Eight types of known volcanic features and associations are described and each assigned a point value based on the degree to which it is thought to be characteristic of volcanoes. The system is applied to four well known Martian volcanoes and to other Martian features which may or may not be volcanic in origin.
Analysis of HCMM data shows that the resolution provided by the thermal data is inadequate to permit the identification of individual lava flows within the volcanic test sites. Thermal data of southern California reveals that dune complexes at Kelso and Algodomes are found to be too small to permit adequate investigation of their structure. As part of the study of the San Francisco volcanic field, marked variations in the thermal properties of the region between Flagstaff and the Utah State border were observed. Several well-defined units within the Grand Canyon and the Colorado Plateau were recognized and appear to be very suitable for analysis with HCMM, SEASAT and LANDSAT images. Although individual volcanic constructs within the Cascade Range are too small to permit detailed characterization with the thermal data, the regional volcano/tectonic setting offers a good opportunity for comparing the possible thermal distinction between this area and sedimentary fold belts such as those found in the eastern United States. Strong intra-regional variations in vegetation cover were also tentatively identified for the Oregon test site.
The distribution fracture patterns of old Martian impact basins were studied. The basaltic plains on the Moon generally occur inside or around impact craters and basins and it is believed that fractures generated by large impacts provided long lasting pathways for magmas. The volcanic plains and volcanic edifices on Mars which show a complex distribution are the interiors of the most obvious old basins are largely buried by wind blown deposits. The Martian ridged plains that most resemble the lunar maria typically are offset from such impact basins. The origin of the mare like plains offset and the placement of the large volcanic mountains are discussed.
Tectoism in the Valles Marineris appears to have been accompanied by volcanism. The proposed volcanic features, though probably contemporaneous with the gigantic ones in the Tharsis area, are composed of small, mafic and, possibly, somewhat larger felsic flows. The size of these features is similar to that of volcanic flows on the Earth.
Geomorphic mapping revealed that the three volcanic constructs within Elysium Planitia (Hecates Tholus, elysium Mons and Albor Tholus) are very different in their overall morphology and represent three distinct types of martian volcano. Hecates Tholus was found to possess the most likely possible example of a young, explosively generated, air fall deposit, while the volume of magma erupted from Elysium Mons appears to have been orders of magnitude larger than that erupted from Albor Tholus. A primary aim of the regional geological analysis of Elysium Planitia is to further understand the volcanic and tectonic evolution of the area by the identification and interpretation of individual lava flows and their source vents. Lava flow size, spatial distribution, flow direction and the stratigraphic relationships of these lava flows to adjacent structural features were all measured. The topographic form of Elysium Mons has totally controlled the flow direction of lava flows within Elysium Planitia. Lava flows from Elysium Mons can be traced for distances of 150 to 250 km in a radial direction from the volcano. Parasitic vents located beyond the recognizable volcanic construct also conform to this radial pattern. A second unusual characteristic of the Elysium Planitia region is the high frequency of occurrence of sinuous channels that are morphologically similar to lunar sinuous rilles.
The discovery of a 4.23 AE, low-Ti composition mare basalt from the Fra Mauro Formation has challenged the hypothesis that the plutonism of the lunar highlands and the mare-type volcanism are two separate problems in both space and time. Attention is presently given to data indicating that non-KREEPy, mare-type volcanism began at least as early as 4.2 AE in the Fra Mauro region, and probably across much of the lunar surface. Massive bombardment during the 'terminal cataclism', and the subsequent veneer of younger mare basalts has obliterated most of the evidence for these ancient volcanic events, which may be related to such basin-forming events as the impact-triggered igneous activity that made Procellarum.
The laser microprobe was used to extend the Ar-39-Ar-40 method to small, low potassium glassy objects in order to determine the ages of Apollo 15 yellow volcanic, green volcanic group A, and green volcanic group D glasses. The apparent solidification ages for these glasses are 3.62 + or -0.07, 3.41 + or -0.12, and 3.35 + or -.18 aeons, respectively. The ages for group A and d green glasses agree well with previously reported ages for aliquots of 'bulk' green glass. No significant difference in the solidification age was found between the A and D groups. The average exposure ages for the yellow and green glasses from 15426 and 15427 were indistinguishable, with ages between 300 and 275 m.y.
Spectral, thermal, radar, and photogeologic data were used to determine the composition and origin of lunar dark-haloed craters. Analyses of reflectance spectra (near-infrared) of dark-haloed craters on light plains indicate that in every instance these craters exposed mare basalts which had previously been covered by varying thicknesses of highlands debris. In the Schiller-Schickard region a relatively thick highlands unit was emplaced as a result of the Orientale impact event. The results of recent remote sensing photogeologic and lunar samples studies indicate that mare volcanism was a significant process during much of the pre-Imbrian epoch and may have been initiated as early as 4.2-4.3 Ga. The very early volcanic episodes contributed materials to the lunar surface which were later incorporated into the upper portion of the highlands crust by subsequent impact mixing. On the basis of the data it is concluded that current models of the extent and duration of mare volcanisms, as well as those involving the composition of thermal evolution of the lunar interior will have to be revised.
There are good reasons to believe that lunar volcanic glasses originated from a deep interior source. The presence of a thin layer of surface correlated elements on these glasses may indicate that the Moon has some reservoirs that are enriched in volatiles. Since the glasses themselves do not show similar enrichment, the source should be of limited extent. Three scenarios are advanced for the origin of these elements. The mechanism for lunar volcanism differs from the mechanism for volcanism on Earth since the former produces bubbling and the latter explosive fountaining. From the condensation behavior of the volatile compounds, which leads to heterogeneous condensation, it is concluded that comparing element ratios of surface correlated elements gives little sense. It seems as if the volatile reservoirs are of rather limited extent and that they do not enlarge the volatile content of the bulk Moon significantly.
On the Colorado Plateau-Basin and Range transition in Arizona and New Mexico, basaltic volcanism takes two physiographic forms: (1) Major central composite volcanoes (e.g., San Francisco Peaks) in which basaltic magma differentiates at shallow crustal levels to siliceous and members and (2) large numbers of small cinder cones and a few domes that result from numerous discrete magma batches which apparently had little opportunity for differentiation. This study represents the first look at the petrogenesis of Plateau-bounding volcanic fields, based on rigorous stratigraphic controls, in combination with major and trace-element constraints. The emerging pattern of large volcanic constructs associated with shallow fractional crystallization, and numerous cinder cones associated with limited or no shallow differentiation may provide an analogue for interpreting petrogenetic patterns and/or tectonic settings on Mars.
Venera 15 and 16 radar images of Venus, together with Earth based data from the Arecibo Observatory, indicate that volcanism has played an important role in the evolution of the Venusian landscape. At the end of this decade, NASA's Venus Radar Mapper (VRM) spacecraft will return near global information that will further constrain the planet's geologic history. Due to the diversity of volcano/tectonic features that have already been identified on Venus, and the intrinsic differences between radar images and conventional photography, additional expertise is being developed with which to interpret the VRM images of this unusual environment. Several attempts to better understand the physical characteristics of volcanic terrains are described here. Pioneer Venus radar altimeter measurements of topographic variability and surface roughness are compared with Goldstone radar measurements of volcanic terrains on Mars. Synthetic aperture radar images obtained by the SIR-B Space Shuttle experiment over Kilauea Volcano, Hawaii, are employed to investigate the differences in radar returns from pahoehoe, aa and sheet lava flows. Four polarization, multiple incidence angle, aircraft radar images of the Medicine Lake area of N. California are used to address the unusually high cross-polarization ratio of lobate flows around Beta Regio on Venus, as measured by the Arecibo radar.
The Solar Backscatter Ultraviolet Experiment (SBUV) aboard the Nimbus-7 satellite identified large amounts of SO2 in the tropical stratosphere on April 15, 1982, 11 days after major eruption of the El Chichon volcano in southern Mexico. It is shown in the present study that the backscattered ultraviolet radiances measured by the SBUV experiment have been strongly affected by the presence of stratospheric volcanic cloud from the El Chichon eruptions. Both SO2 and aerosol amounts present in the volcanic cloud have been mapped on the basis of an analysis of the radiances measured by the SBUV and TOMS (Total Ozone Mapping Spectrometer) experiments. It is estimated that a volcanic cloud of optical depths as small as 0.03 can be detected using SBUV, provided the cloud reaches the middle atmosphere. Lower-altitude clouds have progressively smaller effects on the radiances as well as on the ozone profile derived from them and are therefore harder to detect.
Two investigations were undertaken to examine possible large scale explosive volcanic deposits on Mars. The first includes an analysis of Viking Infrared Thermal Mapper (IRTM) data covering the vast deposits in the Amazonis, Memnonia, and Aeolis regions. These postulated ignimbrites have been previously mapped, and at least five high resolution nighttime IRTM data tracks cross the deposits. Preliminary analysis of the data covering Amazonis Planitia show that local features have anomalous thermal inertias but the ignimbrites as a whole do not consistently have significantly different thermal inertias from their surroundings. Preliminary photogeologic and IRTM studies of the large and small highland paterae have also begun. The purpose of IRTM studies of postulated Martian explosive volcanic deposits is to determine the physical properties of the proposed ignimbrites. If volcanic deposits are exposed at the surface, high thermal inertias, as are observed for Apollinaris Patera, should be present.
A number of extensive linear constructional features occur on the north and east flanks of Alba Patera. They are found in a 150-km-wide zone and comprise aligned ridge elements that are locally associated with short volcanic flows. They are among the youngest volcanic features in the region and are believed to be Martian analogs of terrestrial spatter ridges. On the basis of measurements made on Viking images, it appears that active volcanic fissures on Mars were larger than their terrestrial counterparts.
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.
The Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) is designed for mapping of the atmospheric ozone distribution. Absorption by sulfur dioxide at the same ultraviolet spectral wavelengths makes it possible to observe and resolve the size of volcanic clouds. The sulfur dioxide absorption is discriminated from ozone and water clouds in the data processing by their spectral signatures. Thus, the sulfur dioxide can serve as a tracer which appears in volcanic eruption clouds because it is not present in other clouds. The detection limit with TOMS is close to the theoretical limit due to telemetry signal quantization of 1000 metric tons (5-sigma threshold) within the instrument field of view (50 by 50 km near the nadir). Requirements concerning the use of TOMS in detection of eruptions, geochemical cycles, and volcanic climatic effects are discussed.
The impact of volcanic eruptions on weather and climate is considered. The data from nineteenth-century eruptions is examined, showing the importance of sulfur volatiles for climate change. Information obtained from ice cores is discussed, and the contrasts between the eruptions of Mt. St. Helens and El Chichon are pointed out. The atmospheric effects of the greatest historic eruptions are recalled. The potential for the occurrence of 'volcanic winters' and the possible role of volcanism in mass extinctions are considered.
The analysis of igneous rock distribution has been fulfilled on the basis of the geomorphological map of Mars at scale 1:5,000,000, according to data obtained from interpretation of 1:2,000,000 scale pictures of Mariner 9, Mars 4, Mars 5, Viking 1 and 2. Areological areas are listed as having been distinguished as the stratigraphic basis for a martian time scale. The area of volcanic eruptions and the number of eruptive centers are calculated on 10 x 10 deg cells and for each areological eras. The largest area of eruptive happening at different times is related with Tharsis tectonic uplift. The study of distribution of igneous rock area and volcanic centers number on 10 deg sectors and zones revealed the concentration belts of volcanic formations.