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- All Subjects: Hydrologic sciences
- Creators: Schmeeckle, Mark
Description
ABSTRACT
The Sentinel-Arlington Volcanic Field (SAVF) is the Sentinel Plains lava field and associated volcanic edifices of late Cenozoic alkali olivine basaltic lava flows and minor tephra deposits near the Gila Bend and Painted Rock Mountains, 65 km-100km southwest of Phoenix, Arizona. The SAVF covers ~600 km2 and consists of 21+ volcanic centers, primarily low shield volcanoes ranging from 4-6 km in diameter and 30-200 m in height. The SAVF represents plains-style volcanism, an emplacement style and effusion rate intermediate between flood volcanism and large shield-building volcanism. Because of these characteristics, SAVF is a good analogue to small-volume effusive volcanic centers on Mars, such as those seen the southern flank of Pavonis Mons and in the Tempe Terra region of Mars. The eruptive history of the volcanic field is established through detailed geologic map supplemented by geochemical, paleomagnetic, and geochronological analysis.
Paleomagnetic analyses were completed on 473 oriented core samples from 58 sites. Mean inclination and declination directions were calculated from 8-12 samples at each site. Fifty sites revealed well-grouped natural remanent magnetization vectors after applying alternating field demagnetization. Thirty-nine sites had reversed polarity, eleven had normal polarity. Fifteen unique paleosecular variation inclination and declination directions were identified, six were represented by more than one site with resultant vectors that correlated within a 95% confidence interval. Four reversed sites were radiometrically dated to the Matuyama Chron with ages ranging from 1.08 ± 0.15 Ma to 2.37 ± 0.02 Ma; and one normal polarity site was dated to the Olduvai normal excursion at 1.91 ± 0.59 Ma. Paleomagnetic correlations within a 95% confidence interval were used to extrapolate radiogenic dates. Results reveal 3-5 eruptive stages over ~1.5 Ma in the early Pleistocene and that the SAVF dammed and possibly diverted the lower Gila River multiple times. Preliminary modeling of the median clast size of the terrace deposits suggests a maximum discharge of ~11300 cms (~400,000 cfs) was necessary to transport observed sediment load, which is larger than the historically recorded discharge of the modern Gila River.
The Sentinel-Arlington Volcanic Field (SAVF) is the Sentinel Plains lava field and associated volcanic edifices of late Cenozoic alkali olivine basaltic lava flows and minor tephra deposits near the Gila Bend and Painted Rock Mountains, 65 km-100km southwest of Phoenix, Arizona. The SAVF covers ~600 km2 and consists of 21+ volcanic centers, primarily low shield volcanoes ranging from 4-6 km in diameter and 30-200 m in height. The SAVF represents plains-style volcanism, an emplacement style and effusion rate intermediate between flood volcanism and large shield-building volcanism. Because of these characteristics, SAVF is a good analogue to small-volume effusive volcanic centers on Mars, such as those seen the southern flank of Pavonis Mons and in the Tempe Terra region of Mars. The eruptive history of the volcanic field is established through detailed geologic map supplemented by geochemical, paleomagnetic, and geochronological analysis.
Paleomagnetic analyses were completed on 473 oriented core samples from 58 sites. Mean inclination and declination directions were calculated from 8-12 samples at each site. Fifty sites revealed well-grouped natural remanent magnetization vectors after applying alternating field demagnetization. Thirty-nine sites had reversed polarity, eleven had normal polarity. Fifteen unique paleosecular variation inclination and declination directions were identified, six were represented by more than one site with resultant vectors that correlated within a 95% confidence interval. Four reversed sites were radiometrically dated to the Matuyama Chron with ages ranging from 1.08 ± 0.15 Ma to 2.37 ± 0.02 Ma; and one normal polarity site was dated to the Olduvai normal excursion at 1.91 ± 0.59 Ma. Paleomagnetic correlations within a 95% confidence interval were used to extrapolate radiogenic dates. Results reveal 3-5 eruptive stages over ~1.5 Ma in the early Pleistocene and that the SAVF dammed and possibly diverted the lower Gila River multiple times. Preliminary modeling of the median clast size of the terrace deposits suggests a maximum discharge of ~11300 cms (~400,000 cfs) was necessary to transport observed sediment load, which is larger than the historically recorded discharge of the modern Gila River.
ContributorsCave, Shelby Renee (Author) / Clarke, Amanda (Thesis advisor) / Burt, Donald (Committee member) / Reynolds, Stephen (Committee member) / Semken, Steven (Committee member) / Schmeeckle, Mark (Committee member) / Arizona State University (Publisher)
Created2015
Description
The morphology of mountainous areas is strongly influenced by stream bed incision rates, but most studies of landscape evolution consider erosion at basin scales or larger. The research here attempts to understand the smaller-scale mechanics of erosion on exposed bedrock channels in the conceptual framework of an established saltation-abrasion model by Sklar and Dietrich [2004]. The recirculating flume used in this experiment allows independent control of bed slope, water discharge rate, sediment flux, and sediment grain size – all factors often bundled together in simple models of river incision and typically cross-correlated in natural settings. This study investigates the mechanics of erosion on exposed bedrock channels caused by abrasion of transported particles. Of particular interest are saltating particles, as well as sediment near the threshold between saltation and suspension - sediment vigorously transported but with significant interaction with the bed. The size of these erosive tools are varied over an order of magnitude in mean grain diameter, including a sand of D¬50 = 0.56 mm, and three gravel sizes of 3.39, 4.63, and 5.88 mm. Special consideration was taken to prevent any flow conditions that created a persistent alluvial cover. The erodible concrete substrate is fully exposed at all times during experiments reported here. Rates of erosion into the concrete substrate (a bedrock proxy) were measured by comparing topographic data before and after each experimental run, made possible by a precision laser mounted on a high speed computer-controlled cart. The experimental flume was able to produce flow discharge as high as 75 liters per second, sediment fluxes (of many varieties) up to 215 grams per second, and bed slopes up to 10%. I find a general positive correlation is found between erosion rate and bed slope, shear stress, grain size, and sediment flux.
ContributorsAdams, Mark (Author) / Whipple, Kelin (Thesis advisor) / Heimsath, Arjun (Committee member) / Schmeeckle, Mark (Committee member) / Arizona State University (Publisher)
Created2016
Description
Rivers in steep mountainous landscapes control how, where, and when signals of base-level fall are transmitted to the surrounding topography. In doing so rivers play an important role in determining landscape evolution in response to external controls of tectonics and climate. However, tectonics and climate often covary and understanding how they influence landscape evolution remains a significant challenge. The Hawaiian Islands, where tectonics are minimized but climate signals are amplified, provide an opportunity to better understand how signals of climate are recorded by landscapes. Focusing on the Hawaiian Islands, I examine (1) how variability in rock mass properties and thresholds in sediment mobility determine where waterfalls form or stall along the Nāpali coast of Kauaʻi, (2) I then extend these findings to other volcanoes to test if observed physical limits in flood size, climate, and volcano gradient can determine where waterfalls form, and (3) I explore how thresholds in river incision below waterfalls limit information about the influence of climate on river incision rates. Findings from this analysis show that waterfalls form or stall where the maximum unit stream power is at or below a critical unit stream power for bedrock river incision. Climate appears to have little effect in determining where these conditions are met but where waterfalls stall or form does record information about discharge-area scaling for global maximum observed floods. Below waterfalls the maximum incision depth for rivers on the island of Kauaʻi (which formed ~ 4-5 million years ago) is approximately proportional to the inverse square root of mean annual rainfall. Though maximum river incision depths for some of the younger volcanoes do not exhibit the same dependency on mean annual rainfall rates they are comparable to the maximum incision depths observed on Kauaʻi even though they are a quarter to one-tenth the age of Kauaʻi. Importantly, these patterns of incision can be explained by thresholds in sediment mobility as recorded by river longitudinal profiles and indicate that the Hawaiian Islands are dominated by threshold conditions where signals of climate are recorded in the topography through controls on incision depth but not incision rates.
ContributorsRaming, Logan Wren (Author) / Whipple, Kelin X (Thesis advisor) / Arrowsmith, Ramon (Committee member) / Heimsath, Arjun M. (Committee member) / DeVecchio, Duane E. (Committee member) / Schmeeckle, Mark (Committee member) / Arizona State University (Publisher)
Created2022