OUTLINE-BASED SHAPE ANALYSIS OF CRATERFORMS: IMPLICATIONS FOR ORIGIN

All natural forms carry properties indicative of their origin and evolution. Shape is fundamental to studies of geology and the shapes of volcanic craterforms are genetically related to the process, or processes, by which they form. Jupiter's moon Io contains irregular craters with scalloped edges, known as paterae. Paterae are inferred volcanic collapse features; however, much remains unknown about the processes by which they form. Currently, the primary method used to identify craterforms is morphologic classification and comparison with terrestrial analogs. A quantitative, shape-based classification system could support qualitative conclusions and would enable comparisons with other landforms.

Outline-based shape analysis is used to investigate the connection between crater morphology and mechanism of formation. We employ geometric morphometrics (commonly used by paleontologists to examine fossil shapes); this method removes all non-shape variables including scale, translation, and rotation to isolate shape for controlled comparisons. Specifically, Eigenshape and Euclidean Distance Matrix analysis were used to quantify and then compare the morphology of terrestrial ash-flow collapse calderas and basaltic shield volcanoes, lunar impact craters, and calderas on Mars with paterae on Io, to examine which processes might be genetically related to patera formation.

Results from outline-based shape analysis show that impact craters are easily distinguished from other structures and paterae are morphologically similar to collapse calderas. Further, the results support that the methods of this study are an effective way to quantify and compare crater morphology. If the shapes of volcanic craterforms and mechanisms of formation can be genetically linked using quantitative classifications, new insights in the formation process of paterae on Io may be revealed.