GeosciencesIncludes Geophysicshttp://hdl.handle.net/11122/130472024-03-28T15:44:13Z2024-03-28T15:44:13ZThe relationship between fracturing, asymmetric folding, and normal faulting in Lisburne Group carbonates: West Porcupine Lake Valley, Northeastern Brooks Range, AlaskaShackleton, John Ryanhttp://hdl.handle.net/11122/149332024-03-27T01:02:39Z2003-05-01T00:00:00ZThe relationship between fracturing, asymmetric folding, and normal faulting in Lisburne Group carbonates: West Porcupine Lake Valley, Northeastern Brooks Range, Alaska
Shackleton, John Ryan
The distribution of fold related fractures and other mesoscopic structures in asymmetrically folded Mississippian to Pennsylvanian Lisbume Group carbonates gives clues concerning the mechanism of folding. Since fracture sets pre-date and post-date folding, it is important, but sometimes difficult, to determine which fracture sets are related to folding. Higher density of fold related fractures and dissolution cleavage in the hinges than limbs of two folds in the study area is evidence for fixed hinge detachment folding. However, geometric modeling of box shaped folds in the study area suggests that some folds may have formed by either detachment folding or trishear fault propagation folding.
Formulaic modeling of fracture density in a stratigraphic section using stratigraphic attributes such as lithology, bed thickness, and chert content predicts general trends in fracture density, but other factors such as slip along bed contacts may obscure the relationship between fracture density, lithology and bed thickness.
Thesis (M.S.) University of Alaska Fairbanks, 2003
2003-05-01T00:00:00ZInstability and retreat of a lake-calving terminus, Mendenhall Glacier, Southeast AlaskaBoyce, Eleanorhttp://hdl.handle.net/11122/149252024-03-23T01:02:51Z2006-05-01T00:00:00ZInstability and retreat of a lake-calving terminus, Mendenhall Glacier, Southeast Alaska
Boyce, Eleanor
Mendenhall Glacier is a lake-calving glacier in southeastern Alaska that is experiencing substantial thinning and increasingly rapid recession. Long-term mass wastage linked to climatic trends is responsible for thinning of the lower glacier and leaving the terminus vulnerable to buoyancy-driven calving and accelerated retreat. Bedrock topography may
play a role in stabilizing the terminus between periods of rapid calving and retreat. Lake-terminating glaciers form a population distinct from both tidewater glaciers and polar ice tongues, with some similarities to both groups. Lacustrine termini experience fewer perturbations (e.g. tidal flexure, high subaqueous melt rates) and are therefore inherently more stable than tidewater termini. At Mendenhall, rapid thinning and simultaneous retreat into a deeper basin leci to floatation conditions along approximately 50% of the calving front. This unstable terminus geometry lasted for ~ 2 years anci culminated in large-scale calving and terminus collapse during summer 2004. We used a 1-dimensional viscoelastic model to investigate the transient response of a floating glacier tongue to buoyant forcing. Results suggest that creep may be capable of accommodating buoyant torque if it is applied gradually. As unresolved bending stresses approach the tensile strength of ice, small rapidly applied perturbations may cause buoyancy-driven calving.
Thesis (M.S.) University of Alaska Fairbanks, 2006
2006-05-01T00:00:00ZCharacterization of geohazards via seismic and acoustic wavesToney, Liamhttp://hdl.handle.net/11122/146512023-10-27T21:08:51Z2023-08-01T00:00:00ZCharacterization of geohazards via seismic and acoustic waves
Toney, Liam
Earth processes, such as large landslides and volcanic eruptions, occur globally and can be hazardous to life and property. Geophysics -- the quantitative study of Earth processes and properties -- is used to monitor and rapidly respond to these geohazards. In particular, seismoacoustics, which is the joint study of seismic waves in the solid Earth and acoustic waves in Earth's atmosphere, has been proven effective for a variety of geophysical monitoring tasks. Typically, the acoustic waves studied are infrasonic: They have frequencies less than 20 hertz, which is below the threshold of human hearing. In this dissertation, we use seismic and acoustic waves and techniques to characterize geohazards, and we examine the propagation of the waves themselves to better understand how seismoacoustic energy is transformed on its path from a given source to the measurement location. Chapter 1 provides a broad overview of seismoacoustics tailored to this dissertation. In Chapter 2, we use seismic and acoustic waves to reconstruct the dynamics of two very large, and highly similar, ice and rock avalanches occurring in 2016 and 2019 on Iliamna Volcano (Alaska). We determine their trajectories using seismic data from distant stations, demonstrating the feasibility of remote seismic landslide characterization. Chapter 3 details the application of machine learning to a rich volcano infrasound dataset consisting of thousands of explosions recorded at Yasur Volcano (Vanuatu) over six days in 2016. We automatically generate a labeled catalog of infrasound waveforms associated to two different locations in Yasur's summit crater, and use this catalog to test different strategies for transforming the waveforms prior to classification model input. In Chapter 4, we use the coupling of atmospheric waves into the Earth to leverage a dense network of about 900 seismometers around Mount Saint Helens volcano (Washington state) as a quasi-infrasound network. We use buried explosions from a 2014 experiment as sources of infrasound. The dense spatial wavefield measurements permit detailed examination of the effects of wind and topography on infrasound propagation. Finally, in Chapter 5 we conclude with some discussion of future work and additional seismoacoustic topics.
Thesis (Ph.D.) University of Alaska Fairbanks, 2023
2023-08-01T00:00:00ZA reinterpretation of Nanuqsaurus hoglundi (Tyrannosauridae) from the late cretaceous Prince Creek formation, northern AlaskaPerry, Zackary R.http://hdl.handle.net/11122/146452023-10-08T01:02:06Z2023-08-01T00:00:00ZA reinterpretation of Nanuqsaurus hoglundi (Tyrannosauridae) from the late cretaceous Prince Creek formation, northern Alaska
Perry, Zackary R.
The Late Cretaceous (late Campanian, ca. 72.8 Ma) Prince Creek Formation on the North Slope of Alaska is well-known for preserving the highest latitude dinosaur fauna in either hemisphere. Within this diverse dinosaurian fauna, a single tyrannosaurid theropod has been described: Nanuqsaurus hoglundi. Little work has been devoted to the taxon since 2014, when it was initially described based on three fragmentary cranial bones. Notably, it was characterized as a "diminutive" taxon, thought to have been substantially smaller than related Late Cretaceous tyrannosaurid species. New cranial and postcranial material attributable to the taxon collected by and housed at the University of Alaska Museum, challenges many aspects of its anatomy, size, and paleobiology. Here, I incorporate new specimens and critically reanalyze the holotype material to address the taxonomic validity of Nanuqsaurus. Further, I conduct the first quantitative analysis to assess body size and test the hypothesis that the Alaskan tyrannosaurid is a diminutive taxon. New material (such as the proximal condyle of a metatarsal and a complete dorsal rib) allowed for the first histological analysis of the Alaskan taxon to be performed to better understand growth dynamics for the taxon and the ontogenetic status of these key specimens. Both specimens are revealed to have been at least 14 years of age at the time of their death and lack an external fundamental system, suggesting that growth had not stopped. New data also facilitates a critical taxonomic re-evaluation of N. hoglundi, which results in a more robust phylogenetic analysis and designation of the taxon as a nomen dubium. Direct proportional scaling of new material suggests a body size comparable to other Late Cretaceous tyrannosaurid taxa, such as Albertosaurus, Gorgosaurus, and Daspletosaurus (all 9 - 10 m body length). Application of theropod regression equations suggests a body size approaching these taxa (at approximately 8 m in length), and a much larger body mass than originally hypothesized (1615 - 1900 kg). The updated size warrants an examination of previously drawn paleobiological conclusions, such as a decrease in body size to reach an "optimal predator size" or as a response to a lack of resources. Regardless of the validity of the taxon, these data collectively provide new insights into the ecology and life history strategies of the northernmost large-bodied theropod known.
Thesis (M.S.) University of Alaska Fairbanks, 2023
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