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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The late Holoce 14C reservoir age in the Chukchi Sea as inferred from tephra in marine sediments

Varhelyi, Aron January 2016 (has links)
Volcanic ash, or tephra, blankets the local and regional landscape following a volcanic eruption. If this ash layer is preserved and identified, it can act as a time synchronous marker bed (isochron) for correlation between marine, terrestrial, glacial and lacustrine deposits. This can be a powerful tool when attempting to determine the true age of a marine sample (e.g. clam or mollusk), affected by the marine reservoir effect (MRE). The MRE causes dated radiocarbon to appear the age that carbon was last in equilibrium with the atmosphere rather than the time that a dated material was deposited. The offset (in years) caused by the MRE is referred to as ΔR. Presented in this study is new data on the lowermost part of SWERUS-L2-2-PC1 (2PC), a marine sedimentary core retrieved from the Chukchi shelf north of Siberia. By using quantification of rhyolitic tephra to locate tephra-rich layers for further study, results show a thick layer that is interpreted to have originated from the caldera-forming eruption of Aniakchak (Aniakchak II). The geochemical identification of the tephra was done using electron probe micro-analysis. A grain size analysis was also conducted to learn more about the sedimentology of 2PC and the possible proxies that can be used when trying to determine where to place the isochron. The isochron was finally placed with the help of relevant literature and the results from this study. That position shifted the previous age model of 2PC at a position to yield a ΔR of 482 years for the Chukchi Sea during this time period.
2

Geochemical fingerprinting of Icelandic silicic Holocene tephra layers

Meara, Rhian Hedd January 2012 (has links)
The overall aim of this research project has been to develop a reference dataset of 19 Holocene silicic Icelandic tephra layers sourced from the Torfajökull, Askja, Katla, Öræfajökull and Hekla volcanic systems. The dataset comprises geochemical data (including major, trace and rare earth element data for bulk and glass phases collected by XRF, electron microprobe, ion probe and laser ablation ICP-MS) and physical data (including sedimentary logs, field photographs, distribution maps and GPS localities of reference sections). Results indicate that Icelandic volcanic systems show unique geochemical signatures which result from the systems proximity to the active rifting zone and the proposed upwelling mantle plume that underlies the island. Within individual volcanic systems, eruptions produce tephra with distinct geochemical characteristics, which allow for the independent confirmation of tephra identity. The identification and discrimination of tephra layers can in some cases be achieved using major element chemistry (e.g. Hekla, H1104 – H5) while other tephra layers can only be discriminated using trace element chemistry (e.g. Torfajökull, Landnám and Gràkolla). Certain tephra layers however show near-identical geochemistry and therefore discrimination is not possible (e.g. Hekla, HA, HB, HC, HM, HN, HX, HY, HZ) without the incorporation of other proxy data. Icelandic micro-tephra horizons are identified in soil, lacustrine and marine sedimentary sequences and are used for dating and correlation in Quaternary studies. Data collected for this project will facilitate reliable data comparison and tephra identification between proximal and distal localities across the North Atlantic region. The data may also contribute to the debate regarding the formation of silicic rocks within Iceland, particularly with regard to the Hekla central volcano. The geochemical data collected for this thesis shows distinct age-dependant geochemical sub-groups suggesting temporal sub-surface relocation of the Hekla magma source.
3

Vulnerability of Pastoral Farming Systems to Volcanic Ashfall Hazards

Wilson, Thomas McDonald January 2009 (has links)
Volcanic eruptions are powerful, spectacular, uncontrollable geophysical events which require management to mitigate loss of life and property. An essential part of volcanic risk management is to quantify the vulnerability of exposed elements of society to volcanic hazard. Agriculture takes advantage of the fertile soils of volcanic regions, but is vulnerable to damage and disruption from volcanic hazards, in particular ashfall. This thesis investigates the vulnerability of pastoral agriculture to volcanic ashfall by examining impacts on the resource base of pastoral farming (water supply, pasture and soil, and livestock) and explores mitigation and recovery strategies for ashfall hazards at varying levels. It provides a quantitative understanding of pastoral farming vulnerability to ashfall hazards, as part of probabilistic risk assessment. Surface farm water supplies are found to be more vulnerable to ashfall, through contamination and sedimentation, than groundwater supplies. After heavy ashfall, the physical impacts of ashfall overwhelm the more subtle chemical impacts on water supply systems, but even relatively thin ashfalls may cause potential toxic changes to water quality. Farm-scale assessment of water supplies was used to identify key areas of vulnerability to ash hazards. Modelling a large-scale evacuation of livestock following widespread, heavy ashfall found the logistical, time and cost requirements high and may make this action unrealistic. Perhaps most critically, it is doubtful that farms in surrounding regions have the capacity to accommodate the numbers of animals likely to be affected. Tunnel-house and field trials have shown pastures are relatively resilient to ashfalls of 10 mm, but this resilience rapidly reduces with increasing ashfall thickness and at .100 mm there is effectively no pasture recovery. Ashfall grain size, frequency, soluble salt volume, and different meteorological conditions also have a significant impact on pastures and soils. Pasture reestablishment will benefit from tillage of ash covered soils to mix ash and topsoil and break up the surface crust which may form on ash deposits. Targeted fertiliser treatments may also be required to buffer acidic soluble salts and remedy deficiencies of essential nutrients. Reworking of ash deposits was found to be highly disruptive to pasture re-establishment and in extreme cases may prolong and intensify the impacts following an ashfall. The majority of farmers impacted by ashfall will continue farming, albeit with varying levels of disruption. However real or perceived impacts to human health may result in farm evacuation in the short-term. Where ashfall thicknesses are too thick for a return to profitable farming, migration from impacted farms and agriculture-related industries will result in significant demographic changes to rural communities and potential social impacts. Stressed farming systems are most vulnerable to failure and psychosocial impacts.
4

Vulnerability Assessment and Risk Mitigation: The Case of Vulcano Island, Italy

Galderisi, Adriana, Bonadonna, Costanza, Delmonaco, Giuseppe, Ferrara, Floriana Federica, Menoni, Scira, Ceudech, Andrea, Biass, Sebastien, Frischknecht, Corine, Manzella, Irene, Minucci, Guido, Gregg, Chris 01 January 2013 (has links)
This paper reports on a comprehensive vulnerability analysis based on a research work developed within the EC ENSURE Project (7FP) dealing with the assessment of different volcanic phenomena and induced mass-movements on Vulcano Island (S Italy) as a key tool for proactive efforts for multi-risk mitigation. The work is mainly focused on tephra sedimentation and lahar hazards and related physical, systemic and mitigation capacities.
5

Vulnerability Assessment and Risk Mitigation: The Case of Vulcano Island, Italy

Galderisi, Adriana, Bonadonna, Costanza, Delmonaco, Giuseppe, Ferrara, Floriana Federica, Menoni, Scira, Ceudech, Andrea, Biass, Sebastien, Frischknecht, Corine, Manzella, Irene, Minucci, Guido, Gregg, Chris 01 January 2013 (has links)
This paper reports on a comprehensive vulnerability analysis based on a research work developed within the EC ENSURE Project (7FP) dealing with the assessment of different volcanic phenomena and induced mass-movements on Vulcano Island (S Italy) as a key tool for proactive efforts for multi-risk mitigation. The work is mainly focused on tephra sedimentation and lahar hazards and related physical, systemic and mitigation capacities.
6

Tephrostratigraphy and paleoenvironments of the late Quaternary in eastern Beringia

Jensen, Britta J.L. Unknown Date
No description available.
7

Ash, Gas and Computers: the vulnerability of laptop computers to volcanic hazards

Wilson, Grant Michael January 2011 (has links)
Volcanic eruptions are powerful, uncontrollable natural events which produce a number of hazards that can impact upon all aspects of society, including critical infrastructure. The most widespread and disruptive of these hazards is volcanic ashfall. Direct ashfall impacts, even minor, can cause multiple knock on effects throughout all critical infrastructure sectors leading to disruption of these services, on which society relies. However with appropriate volcanic risk management strategies, these impacts can be lessened. Electronic equipment, including laptop computers, are a common and vital component in all critical infrastructure sectors, field based volcanic research and wider society. Therefore, it is important to understand how laptops will function in volcanic environments. This thesis assesses the vulnerability of laptop computers to volcanic ash and gas hazards through field and laboratory based experimentation and the development of quantitative risk assessments metrics. Laboratory based ash vulnerability experiments were carried out in the Volcanic Ash Testing Facility, University of Canterbury, using a mass produced basalt ‘pseudo ash’, which is physically and chemically analogous to fresh volcanic ash. Each laptop was exposed to ash for 100 160 hours at fall rates of ~500 g/m² h. None of the ten laptops used sustained any permanent damage from volcanic ash, however, three shutdown temporarily due to overheating. This was because laptops only contain a few small ventilation holes which prevent large quantities of ash from entering the laptops. However, ash contamination reduced functionality of keyboards, CD drives and some cooling fans as these are open to the environment or located close to ventilation holes. Wet ash, known to cause short circuits of electrical equipment, was not able to enter the laptops because it is less mobile than dry ash. Functionality was retained with the use of simple mitigation techniques such as placing laptops inside heavy duty polyethylene bags. Volcanic gas vulnerability experiments were undertaken at White Island, New Zealand. Three laptops were exposed to high concentrations of volcanic gases for ~5 hours. None however, sustained any permanent damage, due to the limited quantity of gas that could enter the laptop, although metal components on the outside of the laptop sustained minor corrosion.
8

Reconstructing the Generation, Evolution, and Migration of Arc Magmatism using the Whole-rock Geochemistry of Bentonites: A Case Study from the Cretaceous Idaho-Farallon Arc System

Hannon, Jeffrey S. January 2020 (has links)
No description available.
9

Tephrochronology of the Last Glacial/Interglacial transition in western Småland, southwestern Sweden

Morén, Björn January 2009 (has links)
<p>Tephrochronology, or the dating and correlation of stratigraphic sediment sequences by the use of tephra, is a dating method that has been much refined in the last decade. This refinement has enabled the detection of cryptotephra, which has expanded the known distribution of different tephras. At the site Lake Mulakullegöl in the southwest of Sweden, three distinct tephra horizons have been detected, of which two have been geochemically identified. The identified tephras are the Vedde Ash (ca 12,000 cal. yrs BP) and the Hässeldalen Tephra (ca 11,500 cal. yrs BP), both of Icelandic origin. These tephras were deposited during the middle of the Younger Dryas Stadial and the Younger Dryas/Preboreal transition, respectively. The Vedde Ash is one of the most widespread tephras of Icelandic provenance, while the Hässeldalen Tephra so far only has been found at two sites in southeastern Sweden, prior to the current study. A third, unidentified, tephra was also detected. Based on the stratigraphic position, this tephra might be the Borrobol Tephra, which has been dated to ca 14,400 cal. yrs BP. This might indicate that warming had not yet occurred in this part of Sweden. The extended known distribution of especially the Hässeldalen Tephra, but also the Vedde Ash, has enabled a higher potential for correlations between different records deposited during the Last Glacial/Interglacial transition.</p>
10

Tephrochronology of the Last Glacial/Interglacial transition in western Småland, southwestern Sweden

Morén, Björn January 2009 (has links)
Tephrochronology, or the dating and correlation of stratigraphic sediment sequences by the use of tephra, is a dating method that has been much refined in the last decade. This refinement has enabled the detection of cryptotephra, which has expanded the known distribution of different tephras. At the site Lake Mulakullegöl in the southwest of Sweden, three distinct tephra horizons have been detected, of which two have been geochemically identified. The identified tephras are the Vedde Ash (ca 12,000 cal. yrs BP) and the Hässeldalen Tephra (ca 11,500 cal. yrs BP), both of Icelandic origin. These tephras were deposited during the middle of the Younger Dryas Stadial and the Younger Dryas/Preboreal transition, respectively. The Vedde Ash is one of the most widespread tephras of Icelandic provenance, while the Hässeldalen Tephra so far only has been found at two sites in southeastern Sweden, prior to the current study. A third, unidentified, tephra was also detected. Based on the stratigraphic position, this tephra might be the Borrobol Tephra, which has been dated to ca 14,400 cal. yrs BP. This might indicate that warming had not yet occurred in this part of Sweden. The extended known distribution of especially the Hässeldalen Tephra, but also the Vedde Ash, has enabled a higher potential for correlations between different records deposited during the Last Glacial/Interglacial transition.

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