School of Geography - Theses

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    Craterform morphology and morphometry : a planetary perspective on maar volcanism and meteorite impact
    Bishop, Mark A. ( 1990)
    The use of the morphometric measurements, rim crest diameter (Dr) and circularity (C), are evaluated and shown to provide a quantitative method of determining a craterform's origin. Although numerous methods exist to determine these parameters, the method termed circumscibing-inscribing circles (Dr2) and (C2), has proven the most accurate and reliable technique with which to measure a crater's planimetric profile. The measurement of circularity for terrestrial craterforms less than five kilometers across has provided a benchmark which will distinguish between maar volcano and meteorite impact craters. Using this technique, the average accuracy for segregating maar and impact morphologies, is shown to be approximately 85 percent. Comparisons with other methods of mensuration show that the morphological signature of each crater type is most effectively expressed by measuring (C2). Although this technique is statistically simple, it is superior when compared with analyses that use a multivariate approach on craters of these dimensions. Using the established technique and limits for determining a terrestrial craterform's mode of origin, the application of (Dr2) and (C2) to the Lunar Alphonsus Dark Halo Craters, gives additional support to previous investigations that indicate these features to be of pyroclastic origin resembling maar-like volcanoes. The accurate classification of crater origin is an important aspect for both stratigraphie interpretation and the relative dating of planetary surfaces. Morphometric analysis as undertaken in this study, will be of immediate use in the interpretation of the Magellan radar imagery of Venus during 1991. It is therefore evident that the interpretation of planetary landscapes using geomorphology, is a worthy contribution to the earth and planetary sciences.