Understanding vertical and lateral changes in sand-wave facies in dilute pyroclastic density current deposits

Wheeler, Benjamin Harold (2019) Understanding vertical and lateral changes in sand-wave facies in dilute pyroclastic density current deposits. Masters thesis, Northern Arizona University.

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Abstract

Maar-diatreme volcanoes commonly produce sand-waves with features that resemble bedforms found in eolian and fluvial deposits, causing difficulty in distinguishing the origin of a deposit, particularly when geologic context is lacking. Bedforms in eolian and fluvial environments have been extensively studied but information is sparse in pyroclastic environments. Pyroclastic deposits from Teshim Butte, Triplets Maar, and Haskie Volcano, located in the Hopi Buttes Volcanic Field AZ as well as Zuni Salt Lake Maar, Afton Craters located in New Mexico, and Ubehebe Crater located in Death Valley California, were studied to define vertical and lateral changes within the sand-wave facies. Stratigraphic sections, grain size, and bedform properties were measured in the field and with photogrammetry and analyzed statistically. Six bedform types were identified and defined based on their physical characteristics. The six types are: small, erosional, elongate, medium type one, medium type two, and large bedforms. Estimate for flow depth and velocity were calculated based on bedform attributes. Key features unique to volcanic bedforms include: low lee-side angles, the co-deposition of coarse and fine material, rapid changes in bedform type, low amplitude bedforms, highly variable wavelengths, and the formation of bedforms with crests and stoss sides preserved. Lee-side angles for volcanic bedforms measured in this study were typically below the angle of repose. Deposition that occurs on the lee slope of volcanic bedforms is not necessarily dependent on gravity-driven avalanches as in eolian and fluvial dunes. Due to the pulsating nature of pyroclastic deposits, bedforms commonly occur as singular features, so each bedform is independent of other bedforms. Fluctuating energy, existing topography, and supply of eruptive material can lead to the six sub-facies occurring in a single vertical section. Depending on location and depth of the explosion loci within the maar-diatreme, bedforms contain juvenile material mixed with lithic material. Bedforms from this study can be used to help in identification of depositional environments in locations where context is lacking or minimal data are available, such as remote sensing studies of bedforms on Mars.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Bedform; Mars; Pyroclastic; SfM; Volcano; Sand waves
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	31 Jan 2022 18:18
Last Modified:	31 Jan 2022 18:18
URI:	https://openknowledge.nau.edu/id/eprint/5609

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