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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.

Rates of rock fracturing as a tool for forecasting eruptions at andesitic-dacitic stratovolcanoes

Smith, Rosanna January 2008 (has links)
Increasing rates of volcano-tectonic (VT) seismicity, produced by rock fracture and slip along faults, are a common precursor to eruptions. Precursory VT seismicity can thus be related to how fractures develop within and below a volcano before it erupts. This study combines field and experimental data to define constraints on theoretical models for accelerating VT seismicity. VT seismicity before all 17 episodes of lava-dome growth at Mount St. Helens between 1980 and 1986 and before eruptions at selected andesitic-dacitic volcanoes following more than a century of repose was analysed. VT precursors developed within three weeks of lava-dome growth episodes, with stronger patterns before eruptions through larger domes, suggesting that the domes themselves inhibited magma ascent. The accelerations fluctuated about mean trends between exponential and hyperbolic, suggesting that individual sequences evolved under different boundary conditions, including applied stress and rock temperature, that determine the rates of seismogenic fracturing. Before the first eruption after a long repose interval, a hyperbolic acceleration in VT seismicity developed over approximately ten days when the eruption was dome building rather than phreatomagmatic. To investigate the effect of changing boundary conditions, samples of andesite were deformed in compression at temperatures up to 900 °C and confining pressures up to 50 MPa with acoustic emissions (AE) recorded as analogues to VT events. There was no temperature or pressure dependence in mechanical properties nor AE precursors to sample failure at temperatures up to 600 °C for all confining pressures tested. This supports the use of models of precursory VT seismicity based on brittle fracture for volcanoes erupting after long repose intervals, where a new magmatic pathway must be formed. High AE rates for samples tested at 900 °C, which is within the brittle-ductile transition, indicate that VT events can originate from hot material within the lava dome and at magma conduit margins.

The Nubium and Imbrium regions on the Moon : a history of mare flows

Bugiolacchi, R. January 2006 (has links)
The objective of my research is to identify, classify, measure, date, and place in a geological context distinctive lava flows within the Nubium and Imbrium regions of the Moon. I used multispectral filter data from the Clementine mission to create regional compositional maps based on the estimated abundance of iron and titanium in the regolith. In addition, by letting the 415 nm, 950 nm, and 750 nm wavebands respectively control the BRG channels, I produced a 'stretched' true colour image. A 'false colour' map was also derived by combining the 415/750, 750/1000, and 750/415 nm ratios this type of image benefits from having albedo differences suppressed and colour differences considerably 'stretched'. Most of the exposed maria unit flows were thus identified, outlined, and classified according to their FeO and TiC2 weight percentage content. I also estimated the basalts' ages by establishing their crater size frequency distribution using Lunar Orbiter and Apollo images. A map produced from the filter ratio 750/950 nm helped identify late extrusive materials, fresh impact ejecta, and newly exposed regolith. Iron content variations in the ejecta blankets of several craters were used to estimate the area's minimum maria thickness at the time of impact. This work also focused on geological formations of outstanding interest related to the igneous history of regions. Finally, most data and results were collected and employed to produce multi-layered geological maps of the Nubium and Imbrium regions.

Volcano infrasound : from laboratory to global scale

Dabrowa, Amy Louise January 2013 (has links)
Volcanic infrasound is detectable at distances up to 10,000 km from the source and increasingly commonly, volcanoes are monitored at local distances using infrasound. As a relatively new area of research, many avenues can be explored to improve techniques for monitoring and interpreting infrasound and a range of approaches are utilised in this thesis. A database was compiled of 110 events at 36 globally distributed volcanoes. Infrasound from these events was searched for and characterised using data from infrasound arrays of the International Monitoring System (IMS) to assess how the IMS could be used to monitor remote volcanoes. The distance at which volcanic events were detected increased with eruption plume height. Amplitude decay rates varied widely, but an amplitude decay rate of l/r (where r is distance to source) was successfully used to compare eruptions. The amplitude and energy of volcanic infrasound was found to increase with plume height, whilst frequency decreased. These characteristics allow a broad estimation of eruption intensity using long-range infrasound data from the IMS alone, and in combination with simple event location methodologies demonstrate how the IMS could be used to monitor remote volcanoes. Infrasound from Mount Erebus, Antarctica, is regularly detected at an infrasound array 25 km distant. Comparing these data with that recorded near the vent allowed study of infrasound propagation effects, and investigation of how volcanoes could be monitored at this distance. The rate of amplitude decay observed between near-vent sensors and an infrasound array 25 km from the vent was greater than expected by purely hemispherical spreading. Decay rates varied between just less than l/r and approaching 1/r2 over the course of just a few days, indicating that varying meteorological conditions are likely to have a strong effect. Of the known infrasound signals, 75% were detected at IS55 and methodology was successfully developed to automatically detect further events. This demonstrates that although the true amplitude of volcanic events would be unknown due to varying amplitude decay rates, volcanoes could still be successfully monitored at this distance in terms of the frequency of occurrence of events. A set of analogue experiments were conducted to offer insights into the processes that may be important during infrasound production at Strombolian eruptions and other similar volcanic events. Bubbles burst at an air-liquid interface whilst being recorded by a pair of microphones and a high speed camera to investigate the effect of bubble volume, fluid viscosity and rupture dynamics. The experimental system exhibited complex behaviour. Sound began concurrently with bubble rupture and varied greatly with radial position around the source exhibiting dipole characteristics. Both acoustic and rupture characteristics; amplitude, frequency and bubble rupture speeds all increase with decreasing viscosity. Audio results are most closely reproduced by a simple model which assumes that the sound produced is due to excitation of the atmosphere by directional mass flow from the bubble.

The flow of rapidly decompressed gum rosin di-ethyl ether and implications for volcanic eruption mechanisms

Ryan, Graham Alexander January 2001 (has links)
No description available.

Volcanic instability and associated uncertainties at Soufrière Hills Volcano, Montserrat and other volcanoes

Burrell, Rhian January 2005 (has links)
No description available.

The validation and use of thermal imaging cameras for quantitative temperature measurements of lava flows

Ball, Matthew Dominic January 2006 (has links)
No description available.

The thermodynamics and fluid mechanics of near-vent processes in explosive volcanic eruptions on the Earth and Mars

Mitchell, Karl Leon January 2000 (has links)
No description available.

Hornblende dehydration during magma decompression

Buckley, Victoria Jane Emma January 2003 (has links)
No description available.

Magma chamber and contamination processes at Albano Maar, Colli Albani volcanic district, Italy

Cross, Joanna Kate January 2013 (has links)
Colli Albani is a quiescent caldera complex located within the Roman Magmatic Province, Italy. The recent Via dei Laghi phreatomagmatic eruptions led to the formation of nested maars. The largest of which is Albano Maar, which has erupted seven times in the last ca. 69 ka. Recently, detailed stratigraphic study has revealed changes in eruptive style through time, between base surge and fall (sub-plinian) and larger volume pyroclastic density current (Giordano et al., 20 lO). The erupted deposits are multi-component, crystal-rich (40-60%) and with a large cumulate and lithic content (15-20%). The multi-component and relatively well preserved nature of the Albano Maar erupted deposits allows for the study of a large cross-section of the magmatic system.

A geophysical study of volcanic processes at a persistently active volcano and at two calderas in a state of unrest

De Zeeuw-van Dalfsen, Elske January 2005 (has links)
No description available.

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