Cave, Julie Ann; (1992) The role of volatiles in the evolution of the surface of Mars. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A review of the evidence concerning the original and current water budgets of Mars is presented. Previous workers have suggested that a sub-surface reservoir of ice may explain the apparent discrepancy between the two estimated budgets, but the nature, origin, distribution, importance and fate of this ice remains controversial. A thorough examination of the Elysium region has been performed to see how well the distribution of this ice layer may be understood. The distribution of all major landforms that may have required the presence of water for their formation is described. After this initial investigation, the research concentrates on the interpretation of impact crater morphology variations, which are potentially capable of indicating the depth and concentration of sub-surface ice. A classification scheme is presented and the details of over 7000 craters are recorded. The region covers a variety of terrain types, ages, latitudes, and altitudes. The ratio of the ejecta diameter to the crater diameter, used as a indication of the ejecta mobility, is investigated as a function of each of these variables. The morphological characteristics of the craters are also examined, with an emphasis being placed on features that may be indicative of sub-surface ice. The results of the analyses are used to construct a more comprehensive account of the distribution and importance of water within the Elysium region than has yet been possible. Evidence of a widespread ground-ice of variable depth and concentration is presented. The ice-distribution is shown to be dependent upon latitude, though its concentration varies with depth and is strongly influenced by geological considerations. Important differences have been detected in the distribution of Southern Highland and Northern Lowland ground-ice. In addition, the ice is enriched at depth in the Elysium Lavas, and nearer to the surface in deposits to the northwest of Elysium Mons and in the Vastitas Borealis Formation. This distribution suggests that several ice-emplacement mechanisms have operated on Mars, including both the enrichment of the deeper ice by juvenile water from beneath the Elysium Volcanic Province, and the redistribution to the Lowlands of a highly concentrated ice-reservoir from a great depth within the Highlands.

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