Matching Items (14)

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Analysis of spacecraft data for the study of diverse lunar volcanism and regolith maturation rates

Description

Lunar Reconnaissance Orbiter (LRO) and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft missions provide new data for investigating the youngest impact craters on Mercury and the Moon, along

Lunar Reconnaissance Orbiter (LRO) and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft missions provide new data for investigating the youngest impact craters on Mercury and the Moon, along with lunar volcanic end-members: ancient silicic and young basaltic volcanism. The LRO Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) in-flight absolute radiometric calibration used ground-based Robotic Lunar Observatory and Hubble Space Telescope data as standards. In-flight radiometric calibration is a small aspect of the entire calibration process but an important improvement upon the pre-flight measurements. Calibrated reflectance data are essential for comparing images from LRO to missions like MESSENGER, thus enabling science through engineering. Relative regolith optical maturation rates on Mercury and the Moon are estimated by comparing young impact crater densities and impact ejecta reflectance, thus empirically testing previous models of faster rates for Mercury relative to the Moon. Regolith maturation due to micrometeorite impacts and solar wind sputtering modies UV-VIS-NIR surface spectra, therefore understanding maturation rates is critical for interpreting remote sensing data from airless bodies. Results determined the regolith optical maturation rate on Mercury is 2 to 4 times faster than on the Moon. The Gruithuisen Domes, three lunar silicic volcanoes, represent relatively rare lunar lithologies possibly similar to rock fragments found in the Apollo sample collection. Lunar nonmare silicic volcanism has implications for lunar magmatic evolution. I estimated a rhyolitic composition using morphologic comparisons of the Gruithuisen Domes, measured from NAC 2-meter-per-pixel digital topographic models (DTMs), with terrestrial silicic dome morphologies and laboratory models of viscoplastic dome growth. Small, morphologically sharp irregular mare patches (IMPs) provide evidence for recent lunar volcanism widely distributed across the nearside lunar maria, which has implications for long-lived nearside magmatism. I identified 75 IMPs (100-5000 meters in dimension) in NAC images and DTMs, and determined stratigraphic relationships between units common to all IMPs. Crater counts give model ages from 18-58 Ma, and morphologic comparisons with young lunar features provided an additional age constraint of <100 Ma. The IMPs formed as low-volume basaltic eruptions significantly later than previous evidence of lunar mare basalt volcanism's end (1-1.2 Ga).

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Created

Date Created
  • 2013

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Transitions in eruption style at silicic volcanoes: from stable domes to pyroclastic flows and explosive plumes

Description

Silicic volcanoes produce many styles of activity over a range of timescales. Eruptions vary from slow effusion of viscous lava over many years to violent explosions lasting several hours. Hazards

Silicic volcanoes produce many styles of activity over a range of timescales. Eruptions vary from slow effusion of viscous lava over many years to violent explosions lasting several hours. Hazards from these eruptions can be far-reaching and persistent, and are compounded by the dense populations often surrounding active volcanoes. I apply and develop satellite and ground-based remote sensing techniques to document eruptions at Merapi and Sinabung Volcanoes in Indonesia. I use numerical models of volcanic activity in combination with my observational data to describe the processes driving different eruption styles, including lava dome growth and collapse, lava flow emplacement, and transitions between effusive and explosive activity.

Both effusive and explosive eruptions have occurred recently at Merapi volcano. I use satellite thermal images to identify variations during the 2006 effusive eruption and a numerical model of magma ascent to explain the mechanisms that controlled those variations. I show that a nearby tectonic earthquake may have triggered the peak phase of the eruption by increasing the overpressure and bubble content of the magma and that the frequency of pyroclastic flows is correlated with eruption rate. In 2010, Merapi erupted explosively but also shifted between rapid dome-building and explosive phases. I explain these variations by the heterogeneous addition of CO2 to the melt from bedrock under conditions favorable to transitions between effusive and explosive styles.

At Sinabung, I use photogrammetry and satellite images to describe the emplacement of a viscous lava flow. I calculate the flow volume (0.1 km3) and average effusion rate (4.4 m3 s-1) and identify active regions of collapse and advance. Advance rate was controlled by the effusion rate and the flow’s yield strength. Pyroclastic flow activity was initially correlated to the decreasing flow advance rate, but was later affected by the underlying topography as the flow inflated and collapsed near the vent, leading to renewed pyroclastic flow activity.

This work describes previously poorly understood mechanisms of silicic lava emplacement, including multiple causes of pyroclastic flows, and improves the understanding, monitoring capability, and hazard assessment of silicic volcanic eruptions.

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Date Created
  • 2016

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Volcanic history of the Tempe volcanic province

Description

Tempe Terra, Mars, has a complex history marked by volcanism and tectonism. Investigation results presented here build on previous work to better determine the volcanic history of the Tempe volcanic

Tempe Terra, Mars, has a complex history marked by volcanism and tectonism. Investigation results presented here build on previous work to better determine the volcanic history of the Tempe volcanic province by identifying and mapping previously undetected vents, characterizing all vents, identifying spatial and temporal trends in eruptive styles, comparing vent density to similar provinces such as the Snake River Plains of Idaho and Syria Planum and determining absolute age relationships among the volcanic features. Crater size-frequency distribution model ages of 120 Ma to 2.4 Ga indicate the province has been active for over half of the planet's history. During that time, age decreases from southwest to northeast, a trend that parallels the dominant orientation of faulting in the region, providing further evidence that volcanic activity in the region is tectonically controlled (or the tectonics is magmatically controlled). Morphological variation with age hints at an evolving magma source (increasing viscosity) or changing eruption conditions (decreasing eruption rate or eruption through thicker lithosphere).

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Created

Date Created
  • 2012

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The ancient rocky surfaces of Mars: analysis of spacecraft data and the development of laboratory instrumentation

Description

Early spacecraft missions to Mars, including the Marnier and Viking orbiters and landers revealed a morphologically and compositionally diverse landscape that reshaped widely held views of Mars. More recent spacecraft

Early spacecraft missions to Mars, including the Marnier and Viking orbiters and landers revealed a morphologically and compositionally diverse landscape that reshaped widely held views of Mars. More recent spacecraft including Mars Global Surveyor, Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, and the Mars Exploration Rovers have further refined, enhanced, and diversified our understanding of Mars. In this dissertation, I take a multiple-path approach to planetary and Mars science including data analysis and instrument development. First, I present several tools necessary to effectively use new, complex datasets by highlighting unique and innovative data processing techniques that allow for the regional to global scale comparison of multiple datasets. Second, I present three studies that characterize several processes on early Mars, where I identify a regional, compositionally distinct, in situ, stratigraphically significant layer in Ganges and Eos Chasmata that formed early in martian history. This layer represents a unique period in martian history where primitive mantle materials were emplaced over large sections of the martian surface. While I originally characterized this layer as an effusive lava flow, based on the newly identified regional or global extent of this layer, I find the only likely scenario for its emplacement is the ejecta deposit of the Borealis Basin forming impact event. I also re-examine high thermal inertia, flat-floored craters identified in Viking data and conclude they are typically more mafic than the surrounding plains and were likely infilled by primitive volcanic materials during, or shortly after the Late Heavy Bombardment. Furthermore, the only plausible source for these magmas is directly related to the impact process, where mantle decompression melting occurs as result of the removal of overlying material by the impactor. Finally, I developed a new laboratory microscopic emission and reflectance spectrometer designed to help improve the interpretation of current remote sensing or in situ data from planetary bodies. I present the design, implementation, calibration, system performance, and preliminary results of this instrument. This instrument is a strong candidate for the next generation in situ rover instruments designed to definitively assess sample mineralogy and petrology while preserving geologic context.

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Agent

Created

Date Created
  • 2012

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Transitions in Eruption Style at La Fossa Cone, Vulcano Island, Italy

Description

Volcanoes can experience multiple eruption styles throughout their eruptive histories. Among the most complex and most common are eruptions of intermediate explosivity, such as Vulcanian and sub-Plinian eruptions. Vulcanian eruptions

Volcanoes can experience multiple eruption styles throughout their eruptive histories. Among the most complex and most common are eruptions of intermediate explosivity, such as Vulcanian and sub-Plinian eruptions. Vulcanian eruptions are characterized by small-scale, short-lived, ash-rich eruptions initiated by the failure of a dense magma plug or overlying dome that had sealed an overpressured conduit. Sub-Plinian eruptions are characterized by sustained columns that reach tens of kilometers in height.

Multiple eruption styles can be observed in a single eruptive sequence. In recent decades, transitions in eruption style during well-documented eruptions have been described in detail, with some workers proposing explanatory mechanisms for the transitions. These proposed mechanisms may be broadly classified into processes at depth, processes in the conduit, or some combination of both.

The present study is focused on the Pietre Cotte sequence because it may have encompassed up to three different eruptive cycles, each representing different degrees of explosivity. The first deposits are composed of repeated layers of fine ash and lapilli composed of latite and rhyolite endmembers, efficiently mixed at sub-cm scales. The thin layers and bubble/crystal textures indicate that the magma underwent numerous decompressions and open-system degassing, and that the eruptions waned with time. The second phase of the sequence appears to have been initiated by cm-scale mixing between a volatile-rich, mafic magma from deeper in the system and a shallow silicic body. Textures indicate that the magma ascended rapidly and experienced little to no open-system degassing. The final phase of the sequence again produced repeated layers of fine ash and lapilli, of uniform trachyte composition, and waned with time. The first and last phases were likely produced in Vulcanian eruptions, while the pumice-rich layers were likely produced in Vulcanian to sub-Plinian eruptions.

In summary, the Pietre Cotte sequence is characterized by up to three magma recharge events in ~200 years. The differences in eruptive style appear to have been controlled by variations in the volatile content of the recharge magma, as well as the efficiency and scale of magma mixing and resulting overpressures.

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Date Created
  • 2020

Investigating Lava Flow Emplacement: Implications for Volcanic Hazards and Planetary Evolution

Description

Lava flow emplacement in the laboratory and on the surface of Mars was investigated. In the laboratory, the effects of unsteady effusion rates at the vent on four modes

Lava flow emplacement in the laboratory and on the surface of Mars was investigated. In the laboratory, the effects of unsteady effusion rates at the vent on four modes of emplacement common to lava flow propagation: resurfacing, marginal breakouts, inflation, and lava tubes was addressed. A total of 222 experiments were conducted using a programmable pump to inject dyed PEG wax into a chilled bath (~ 0° C) in tanks with a roughened base at slopes of 0, 7, 16, and 29°. The experiments were divided into four conditions, which featured increasing or decreasing eruption rates for either 10 or 50 s. The primary controls on modes of emplacement were crust formation, variability in the eruption rate, and duration of the pulsatory flow rate. Resurfacing – although a relatively minor process – is inhibited by an extensive, coherent crust. Inflation requires a competent, flexible crust. Tube formation requires a crust and intermediate to low effusion rates. On Mars, laboratory analogue experiments combined with models that use flow dimensions to estimate emplacement conditions and using high resolution image data and digital terrain models (e.g. THEMIS IR, CTX, HRSC), the eruption rates, viscosities, and yield strengths of 40 lava flows in the Tharsis Volcanic Province have been quantified. These lava flows have lengths, mean widths, and mean thicknesses of 15 – 314 km, 0.5 – 29 km, and 11 – 91 m, respectively. Flow volumes range from ~1 – 430 km3. Based on laboratory experiments, the 40 observed lava flows were erupted at 0.2 – 6.5x103 m3/s, while the Graetz number and Jeffrey’s equation when applied to 34 of 40 lava flows indicates eruption rates and viscosities of 300 – ~3.5 x 104 m3/s and ~105 – 108 Pa s, respectively. Another model which accounts for mass loss to levee formation was applied to a subset of flows, n = 13, and suggests eruption rates and viscosities of ~30 – ~1.2 x 103 m3/s and 4.5 x 106 – ~3 x 107 Pa s, respectively. Emplacement times range from days to centuries indicating the necessity for long-term subsurface conduits capable of delivering enormous volumes of lava to the surface.

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Date Created
  • 2020

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Dynamics of Ices and Fluids on Mars and Kuiper Belt Objects

Description

The seasonal deposition of CO2 on the polar caps is one of the most dynamic processes on Mars and is a dominant driver of the global climate. Remote sensing temperature

The seasonal deposition of CO2 on the polar caps is one of the most dynamic processes on Mars and is a dominant driver of the global climate. Remote sensing temperature and albedo data were used to estimate the subliming mass of CO2 ice on south polar gullies near Sisyphi Cavi. Results showed that column mass abundances range from 400 - 1000 kg.m2 in an area less than 60 km2 in late winter. Complete sublimation of the seasonal caps may occur later than estimated by large-scale studies and is geographically dependent. Seasonal ice depth estimates suggested variations of up to 1.5 m in depth or 75% in porosity at any one time. Interannual variations in these data appeared to correlate with dust activity in the southern hemisphere. Correlation coefficients were used to investigate the relationship between frost-free surface properties and the evolution of the seasonal ice in this region. Ice on high thermal inertia units was found to disappear before any other ice, likely caused by inhibited deposition during fall. Seasonal ice springtime albedo appeared to be predominantly controlled by orientation, with north-facing slopes undergoing brightening initially in spring, then subliming before south-facing slopes. Overall, the state of seasonal ice is far more complex than globally and regionally averaged studies can identify.

The discovery of cryovolcanic features on Charon and the presence of ammonia hydrates on the surfaces of other medium-sized Kuiper Belt Objects suggests that cryovolcanism may be important to their evolution. A two-dimensional, center-point finite difference, thermal hydraulic model was developed to explore the behavior of cryovolcanic conduits on midsized KBOs. Conduits on a Charon-surrogate were shown to maintain flow through over 200 km of crust and mantle down to radii of R = 0.20 m. Radii higher than this became turbulent due to high viscous dissipation and low thermal conductivity. This model was adapted to explore the emplacement of Kubrik Mons. Steady state flow was achieved with a conduit of radius R = 0.02 m for a source chamber at 2.3 km depth. Effusion rates computed from this estimated a 122 - 163 Myr upper limit formation timescale.

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Date Created
  • 2019

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Neotectonics of Java, Indonesia: crustal deformation in the overriding plate of an orthogonal subduction system

Description

Shallow earthquakes in the upper part of the overriding plate of subduction zones can be devastating due to their proximity to population centers despite the smaller rupture extents than

Shallow earthquakes in the upper part of the overriding plate of subduction zones can be devastating due to their proximity to population centers despite the smaller rupture extents than commonly occur on subduction megathrusts that produce the largest earthquakes. Damaging effects can be greater in volcanic arcs like Java because ground shaking is amplified by surficial deposits of uncompacted volcaniclastic sediments. Identifying the upper-plate structures and their potential hazards is key for minimizing the dangers they pose. In particular, the knowledge of the regional stress field and deformation pattern in this region will help us to better understand how subduction and collision affects deformation in this part of the overriding plate. The majority of the upper plate deformation studies have been focused on the deformation in the main thrusts of the fore-arc region. Study of deformation within volcanic arc is limited despite the associated earthquake hazards. In this study, I use maps of active upper-plate structures, earthquake moment tensor data and stress orientation deduced from volcano morphology analysis to characterize the strain field of Java arc. In addition, I use sandbox analog modeling to evaluate the mechanical factors that may be important in controlling deformation. My field- and remotely-based mapping of active faults and folds, supplemented by results from my paleoseismic studies and physical models of the system, suggest that Java’s deformation is distributed over broad areas along small-scale structures. Java is segmented into three main zones based on their distinctive structural patterns and stress orientation. East Java is characterized by NW-SE normal and strike-slip faults, Central Java has E-W folds and thrust faults, and NE-SW strike-slip faults dominate West Java. The sandbox analog models indicate that the strain in response to collision is partitioned into thrusting and strike-slip faulting, with the dominance of margin-normal thrust faulting. My models test the effects of convergence obliquity, geometry, preexisting weaknesses, asperities, and lateral strength contrast. The result suggest that slight variations in convergence obliquity do not affect the deformation pattern significantly, while the margin shape, lateral strength contrast, and perturbation of deformation from asperities each have a greater impact on deformation.

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Date Created
  • 2016

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Investigations of Morphologies and Emplacement Mechanisms of Volcanically-Derived Landforms on the Moon and Mars

Description

Previous workers hypothesized that lunar Localized Pyroclastic Deposits (LPDs) represent products of vulcanian-style eruptions, since some have low proportions of juvenile material. The objective of the first study is to

Previous workers hypothesized that lunar Localized Pyroclastic Deposits (LPDs) represent products of vulcanian-style eruptions, since some have low proportions of juvenile material. The objective of the first study is to determine how juvenile composition, calculated using deposit and vent volumes, varies among LPDs. I used Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (LROC NAC) digital terrain models (DTMs) to generate models of pre-eruption surfaces for 23 LPDs and subtracted them from the NAC DTMs to calculate deposit and vent volumes. Results show that LPDs have a wide range of juvenile compositions and thinning profiles, and that there is a positive relationship between juvenile material proportion and deposit size. These findings indicate there is greater diversity among LPDs than previously understood, and that a simple vulcanian eruption model may only apply to the smallest deposits.

There is consensus that martian outflow channels were formed by catastrophic flooding events, yet many of these channels exhibit lava flow features issuing from the same source as the eroded channels, leading some authors to suggest that lava may have served as their sole agent of erosion. This debate is addressed in two studies that use Context Camera images for photogeologic analysis, geomorphic mapping, and cratering statistics: (1) A study of Mangala Valles showing that it underwent at least two episodes of fluvial activity and at least three episodes of volcanic activity during the Late Amazonian, consistent with alternating episodes of flooding and volcanism. (2) A study of Maja Valles finds that it is thinly draped in lava flows sourced from Lunae Planum to the west, rendering it analogous to the lava-coated Elysium outflow systems. However, the source of eroded channels in Maja Valles is not the source of the its lava flows, which instead issue from south Lunae Planum. The failure of these lava flows to generate any major channels along their path suggests that the channels of Maja Valles are not lava-eroded.

Finally, I describe a method of locating sharp edges in out-of-focus images for application to automated trajectory control systems that use images from fixed-focus cameras to determine proximity to a target.

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Date Created
  • 2018

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The geologic history of central and eastern Ledi-Geraru, Afar, Ethiopia

Description

Sedimentary basins in the Afar Depression, Ethiopia archive the progression of continental breakup, record regional changes in east African climate and volcanism, and host what are arguably the most important

Sedimentary basins in the Afar Depression, Ethiopia archive the progression of continental breakup, record regional changes in east African climate and volcanism, and host what are arguably the most important fossiliferous strata for studying early human evolution and innovation. Significant changes in rift tectonics, climate, and faunal assemblages occur between 3-2.5 million years ago (Ma), but sediments spanning this time period are sparse. In this dissertation, I present the results of a geologic investigation targeting sediments between 3-2.5 Ma in the central and eastern Ledi Geraru (CLG and ELG) field areas in the lower Awash Valley, using a combination of geologic mapping, stratigraphy, and tephra chemistry and dating. At Gulfaytu in CLG, I mapped the northern-most outcrops of the hominin-bearing Hadar Formation (3.8-2.9 Ma), a 20 m-thick section of flat-lying lacustrine sediments containing 8 new tephras that directly overlie the widespread BKT-2 marker beds (2.95 Ma). Paleolake Hadar persisted after 2.95 Ma, and the presence and characteristics of the Busidima Formation (2.7-0.016 Ma) indicates Gulfaytu was affected by a reversal in depositional basin polarity. Combined with regional and geophysical data, I show the Hadar Formation underlying CLG is >300 m thick, supporting the hypothesis that it was the lower Awash Pliocene depocenter. At ELG, I mapped >300 m of sediments spanning 3.0-2.45 Ma. These sediments coarsen upward and show a progression from fluctuating lake conditions to fluvial landscapes and widespread soil development. This is consistent with the temporal change in depositional environments observed elsewhere in the lower Awash Valley, and suggests that these strata are correlative with the Hadar Formation. Furthermore, the strata and basalts at ELG are highly faulted, and overprinted by shifting extension directions attributed to the northern migration of the Afar triple junction. The presence of fossiliferous beds and stone tools makes ELG a high-priority target for anthropological and archaeological research. This study provides a new temporally-calibrated and high-resolution record of deposition, volcanism, and faulting patterns during a period of significant change in the Afar.

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Created

Date Created
  • 2013