Browsing by Subject "Lesser Antilles"

The focus of this work is to use geologic and geophysical methods to better understand the faults and fracture systems at Puna, in southeastern Hawaii, and southern Montserrat, in the Lesser Antilles. The particular interest is understanding and locating the deep fracture networks that are necessary for fluid circulation in hydrothermal systems. The dissertation first presents a study in which identification of large scale faulting places Montserrat into a tectonic context. Then follow studies of Puna and Montserrat that focus on faults and fractures of the deep hydrothermal systems.

The first chapter consists of the results of the SEA-CALIPSO experiment seismic reflection data, recorded on a 48 channel streamer with the active source as a 2600 in3 airgun. This chapter discusses volcaniclastic debris fans off the east coast of Montserrat and faults off the west coast. The work places Montserrat in a transtensional environment (influenced by oblique subduction) as well as in a complex local stress regime. One conclusion is that the stress regime is inconsistent with the larger arc due to the influence of local magmatism and stress.

The second chapter is a seismic study of the Puna hydrothermal system (PHS) along the Kilauea Lower East Rift Zone. The PHS occurs at a left step in the rift, where a fracture network has been formed between fault segments. It is a productive geothermal field, extracting steam and reinjecting cooled, condensed fluids. A network of eight borehole seismometers recorded >6000 earthquakes. Most of the earthquakes are very small (< M.2), and shallow (1-3 km depth), likely the result of hydrothermal fluid reinjection. Deeper earthquakes occur along the rift as well as along the south-dipping fault plane that originates from the rift zone.

Seismic methods applied to the PHS data set, after the initial recording, picking, and locating earthquakes, include a tomographic inversion of the P-wave first arrival data. This model indicates a high seismic velocity under the field that is thought to be an intrusion and the heat source of the hydrothermal system. A shear wave splitting study suggested the PHS fracture system is largely oriented rift-parallel with some orthogonal fractures. Shear wave splitting data also were used in a tomographic inversion for fracture density. The fracture density is high in the PHS, which indicates high permeability and potential for extensive fluid circulation. This has been confirmed by high fluid flow and energy generation. The high fracture density is consistent with the interpretation of a transfer zone between the rift segments where a fracture mesh would be expected. In Puna the transfer zone is a relay ramp.

The results from the PHS are used as an example to examine the proposed hydrothermal system at St. George's Hill, Montserrat. In southern Montserrat, hot springs and fumaroles suggest a deep hydrothermal system heated by local magmatism. A magnetotelluric study obtained resistivity data that suggest focused alteration under southeastern Montserrat that is likely to be along fault segments. Several faults intersect under SGH, making it the probable center of the hydrothermal system. At Puna, and also Krafla, Iceland, where faults interact is an area of increased permeability, acting as a model to be applied to southern Montserrat. The conclusion is that in both Puna and Montserrat large faults interact to produce local areas of stress transfer that lead to fracturing and permeable networks; these networks allow for high-temperature hydrothermal circulation.

Great Britain's 1833 abolition of slavery created an opportunity for enslaved men and women living on Caribbean islands that were within reach, and view, of one another, to secure liberty through relatively short journeys across the sea. “Freedom on the Horizon” explores the cross-imperial movement of French fugitive men and women in Martinique in the wake of the British abolition of slavery and seeks to reconstruct their conceptions of refuge and freedom. Focusing on Dominica, Martinique, and St. Lucia, this dissertation illuminates the complex geopolitical landscape of the Lesser Antilles during a period of staggered abolition processes and examines the consequences that the escapes of Martinique’s fugitives across the sea had on slavery, emancipation, and then apprenticeship in the British and French colonies.“Freedom on the Horizon” argues that marronage by sea was a critical part of processes of emancipation in Dominica, Martinique, and St. Lucia. The mobility of enslaved men and women’s escape practices, in Martinique merged the worlds of intra- and inter-island flight as groups of fugitives combined navigational expertise and geopolitical knowledge to organize their escapes to Dominica to the north and St. Lucia to the south. Successful escapes depended on these fugitives’ ability to escape the surveillance of French and British colonial authorities, and therefore on a deep knowledge and strategic use of waterways and coastal towns. The first half of this dissertation closely examines the rural coastal landscapes of Martinique which served as the primary locations of group escapes. Enslaved men and women of Martinique, often with the aid of free and enslaved men employed in maritime labor, transformed rural shorelines into sites of departure as they boarded canoes and other small sea craft to transport themselves and their families to freedom as refugees of the French empire. Having reconstructed the social geography and routes of escape that Martinique’s fugitives used to pursue freedom in Dominica and St. Lucia, this dissertation explores their experience of liberty in these two colonies under British rule. The presence of Martinique’s fugitives in Dominica and St. Lucia in the midst of complex emancipation processes created a set of legal challenges and bureaucratic conundrums that are well documented in the British archives. In search of refuge, these fugitives made various requests to British authorities, seeking to navigate the possibilities of a changing legal and political environment towards freedom. While some fugitives voluntarily returned to Martinique, others remained in Dominica and St. Lucia, where they experienced the apprenticeship system set up there during the 1830s and influenced the cross-sea escapes of British apprenticed laborers who were also in search of economic opportunities elsewhere in the region. Ultimately, I argue, the actions of Martinique’s fugitives helped to shape the political and legal landscapes around slavery and emancipation in both the British and the French colonies.