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Journal of Geophysical Research

Cinder cone growth modeled after Northeast Crater, Mount Etna, Sicily

Authors

  • Thomas R. McGetchin,

  • Mark Settle,

  • Bernard A. Chouet


Abstract

Northeast crater is a pyroclastic cone near the summit of Mount Etna, built to its present volume (1 ×106 m3) 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° and vertical. Ejecta consists of ash to 1-m bombs. Physical properties of ejecta include median bomb density, 1.53 g/cm3; particle size of ash found locally on the cone, 150 μ; 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 mantle 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.

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