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dc.contributor.authorBart, Gwendolyn Diane
dc.creatorBart, Gwendolyn Dianeen_US
dc.date.accessioned2011-12-05T22:12:46Z
dc.date.available2011-12-05T22:12:46Z
dc.date.issued2007en_US
dc.identifier.urihttp://hdl.handle.net/10150/193987
dc.description.abstractAnalysis of impact craters and their ejecta addresses someunanswered questions about the lunar surface. First I estimatethe regolith depth on the south farside of the Moon to be about40 m, which is significantly deeper than the nearside regolith,estimated to be 3-16 m. This result is obtained by studyinghundred meter diameter flat floored craters, using the method ofQuaide and Oberbeck (J. Geophys. Res., 1968, 73, 5247-5270). This measurement has implications for the formation of the lunarregolith, and for interpretation of samples returned in thefuture by astronauts or automated sample return missions.Next, I report the discovery of a method that distinguishesbetween primary and distant secondary craters in high resolutionplanetary images. For a given crater size, the largest bouldersof secondary craters are significantly larger than those ofprimary craters. The ability to identify distant secondarycraters will help constrain primary production rates of smallcraters and improve surface age determination of small areasbased on small crater counts.Third, I characterize the distributions of boulders ejected from18 lunar impact craters. I find that in large craters, thelargest boulders are preferentially ejected at low velocities(closer to the crater), whereas the largest boulders from smallcraters are ejected over a wider range of ejection velocities. Also, for a given crater size, deeper regolith reduces themaximum ejection velocity attained by a boulder ejected from acrater. I show that this is a logical result of the streamlinesof excavation in an impact when there are no coherent boulders inthe regolith. Cumulative plots of the boulders have slopessteeper than -2, as do secondary craters. This result isexpected because ejecta fragments produce secondary craters.Finally, I describe the morphology of some lunar crater walllandslides that strongly resemble martian gullies, despite thelack of geologically active water on the Moon today or in thepast. The lunar features indicate that alcove-channel-apronmorphology, attributed on Mars to seepage of liquid water, canalso form via a dry landslide mechanism. Therefore alcove-channel-apron morphology is not diagnostic of water carvedgullies.
dc.language.isoENen_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.subjectMoonen_US
dc.subjectMarsen_US
dc.subjectImpact Crateringen_US
dc.subjectBouldersen_US
dc.subjectRegolithen_US
dc.subjectGulliesen_US
dc.titleLunar Surface Geology From Analysis of Impact Craters and Their Ejectaen_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.contributor.chairMelosh, H. Jayen_US
dc.identifier.oclc659747222en_US
thesis.degree.grantorUniversity of Arizonaen_US
thesis.degree.leveldoctoralen_US
dc.contributor.committeememberMcEwen, Alfred S.en_US
dc.contributor.committeememberTurtle, Elizabeth P.en_US
dc.contributor.committeememberSwindle, Timothy D.en_US
dc.contributor.committeememberHubbard, William B.en_US
dc.contributor.committeememberShowman, Adam P.en_US
dc.identifier.proquest2112en_US
thesis.degree.disciplinePlanetary Sciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.namePhDen_US
refterms.dateFOA2018-08-24T21:40:04Z
html.description.abstractAnalysis of impact craters and their ejecta addresses someunanswered questions about the lunar surface. First I estimatethe regolith depth on the south farside of the Moon to be about40 m, which is significantly deeper than the nearside regolith,estimated to be 3-16 m. This result is obtained by studyinghundred meter diameter flat floored craters, using the method ofQuaide and Oberbeck (J. Geophys. Res., 1968, 73, 5247-5270). This measurement has implications for the formation of the lunarregolith, and for interpretation of samples returned in thefuture by astronauts or automated sample return missions.Next, I report the discovery of a method that distinguishesbetween primary and distant secondary craters in high resolutionplanetary images. For a given crater size, the largest bouldersof secondary craters are significantly larger than those ofprimary craters. The ability to identify distant secondarycraters will help constrain primary production rates of smallcraters and improve surface age determination of small areasbased on small crater counts.Third, I characterize the distributions of boulders ejected from18 lunar impact craters. I find that in large craters, thelargest boulders are preferentially ejected at low velocities(closer to the crater), whereas the largest boulders from smallcraters are ejected over a wider range of ejection velocities. Also, for a given crater size, deeper regolith reduces themaximum ejection velocity attained by a boulder ejected from acrater. I show that this is a logical result of the streamlinesof excavation in an impact when there are no coherent boulders inthe regolith. Cumulative plots of the boulders have slopessteeper than -2, as do secondary craters. This result isexpected because ejecta fragments produce secondary craters.Finally, I describe the morphology of some lunar crater walllandslides that strongly resemble martian gullies, despite thelack of geologically active water on the Moon today or in thepast. The lunar features indicate that alcove-channel-apronmorphology, attributed on Mars to seepage of liquid water, canalso form via a dry landslide mechanism. Therefore alcove-channel-apron morphology is not diagnostic of water carvedgullies.


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