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Northeast crater is a pyroclastic cone near the summit of Mount Etna, built to its present volume (1 X 108 m s) by nearly constant strombolian activity since its birth in 1911. Detailed analysis of one typical photograph of a June 1969 eruption indicates that particles exit with a median velocity of about 51 m/s at angles distributed nearly uniformly between 70 ø and vertical. Ejecta consists of ash to 1-m bombs. Physical properties of ejecta include median bomb density, 1.53 g/cmS; particle size of ash found locally on the cone, 150 •t; median size of bombs constituting the cone, 15 cm; sphericity of bombs, 0.78; and surface roughness of bombs, approximately 0.05. Ballistic analysis using these data and including effects of atmospheric drag shows that cinder cone morphology can be predicted by a quantitative model that is in excellent agreement with observed cone features. Cone shape or profile, rim location, limit of continuous ejecta, the ballistic limit (maximum range of ejected fragments), and the size and location of talus slopes are uniquely determined by fragment exit conditions and ballistics. The model suggests that cinder cones grow through four distinct stages: (1) simple cone, with ma.ntle bedding and a low rounded rim, (2) onset of an exterior talus slope, (3) destruction of the original rounded rim by backward migration of the talus, and (4) outward growth of the talus slope beyond the ballistic limit. In the lunar exterior ballistic environment, cinder cones (if they erupted at conditions qualitatively similar to Etna's Northeast crater) should form tuff rings with low, barely discernible rims. Small dark halo craters and dark mantling deposits observed on the moon (such as those near the Apollo 17 site) may be lunar equivalents of normal terrestrial cinder cones. Clusters of such lunar cones might form continuous blankets rather than groups of discrete cones as they do on the earth. Martian cones, formed under the same conditions, would be more like lunar cones than terrestrial ones. This paper presents results of a study of the mode of growth of cinder cones. It focuses on structure, physical properties of ejecta, ballistics, and growth of Northeast crater, a young pyroclastic cone that originated in 1911 near the summit of Mount Etna, Sicily. We describe the cone and the physical properties of the ejecta and relate these properties to the ballistics of the ejecta revealed by an analysis of a photograph taken of Northeast crater in a typical state of eruption in June 1969. From the eruption photography we obtain statistics on ejection velocity and ejection angle for the ejected particles. We use these data to discuss two problems: (1) the mode of growth of Northeast crater and of cinder cones in general and (2) the structure and surface morphology of cinder cones such as Northeast crater on the surface of Mars and the moon, if they were formed under similar eruption conditions. Both problems are approached by exploring the distribution of ejecta and the growth of cones by repeated similar erupti...

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Sulfurous gases released at the surface of Mars during episodes of volcanic activity would be naturally transported into the upper levels of the Martian atmosphere (20-to 30-km altitude) owing to the synoptic convergence of lower-level winds in the Tharsis region of the planet. The circulation of the upper atmosphere would globally disperse such gases over time scales of 25 earth days. The rate limiting step in sulfate aerosol formation on Mars is inferred to be the gas phase oxidation of SO2 which is accomplished via chemical reactions with O, OH, and HOe. Under present-day atmospheric conditions aerosol formation would occur over periods of several thousand earth days. However atmospheric concentrations of odd hydrogen species (OH, HO2) should increase significantly during periods of persistent surface volcanism. Under these circumstances sulfate aerosol formation could occur on time scales of several hundred earth days. Submicron-sized aerosol particles would circuit Mars several dozen times before they are removed from the atmosphere by gravitational forces. Such aerosols would be globally dispersed and would be deposited over a wide range of equatorial and mid-latitudes. Volcanic sulfate aerosols on Mars are inferred to consist of liquid droplets and liquid-solid slurries containing aqueous solutions of sulfuric acid. These acidic solutions would be chemically reactive and would trigger leaching processes within surface materials upon deposition. Sulfate aerosol deposition is a viable mechanism for transporting sulfur to the Viking lander sites. Atmospheric circulation models indicate that time-averaged vertical winds over Chryse Planitia and Utopia Planitia are directed toward the surface during most Martian seasons. Aerosol particles settling out of the atmosphere would be expected to be preferentially deposited in these regions. Aerosol deposition on a global or hemispheric scale could account for the similar concentrations of sulfur within surficial soils at the two Viking lander sites. VOLCANIC DEGASSING ON MARS Volcanic activity at the surface of Mars has produced enormous shield volcanoes and areally extensive lava plains. The morphology and morphometry of these landforms suggest that Martian eruptions have been largely extrusive in nature [Carr, 1973; Carr et al., 1977; $chaber et al., 1978]. Individual lava flows observed in the Tharsis region commonly extend over distances of several hundred kilometers. Detailed examination of flow lobe thicknesses, channel structure, and Paper number 9C 1310.