A new impact crater morphology: The Peripheral Peak Ring
AuthorNycz, Jason Conrad
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AbstractThe peripheral peak ring (PPR) is a newly recognized impact crater morphologic element observed in both simple and complex Martian impact craters. Although occurring in craters in all regions of Mars, PPR are more frequently observed in the Planitias and Planums. PPR are large blocks of material that detach and separate from the crater rim at the end of the crater modification stage. They can exist as single or multiple monolithic blocks, or rings of rubble. They are thought to be caused when the newly formed crater rim fails. Topographic data show that movement of PPR blocks is primarily lateral (and radial), as opposed to vertical (as is the case with slump blocks). In PPR craters where high resolution images exist, dark layers are observed in the upper crater rims. Thermal infra-red spectroscopy and thermal inertia data suggest this dark layering is either basalt, or basaltic andesite. Increased loading resulting from these dark layers is shown to reduce the stability of the post modification crater rim and could be a contributing factor for PPR formation. PPR are analogous to terrestrial block slides; the latter form when excavation at the toe of the slope results in a lack of confining pressure. Failure then occurs along a low angle plane of weakness. Slope limit equilibrium and finite element modeling constrain the strength properties of the upper Martian crust, and develop a general model of PPR formation. PPR can form without the existence of pore pressure, but they will not form without planes of weakness underneath the crater rim at the end of crater formation. PPR can be used to probe the strength characteristics of the uppermost layers of the Martian crust.
CitationNycz, J. C. (2012). A new impact crater morphology: The Peripheral Peak Ring (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/24867
InstitutionUniversity of Calgary
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