Thesis (M.S.)-Oregon State University, 1988. / Includes bibliographical references (leaves 74-80). Also available via the Internet.

Thesis (M.S.)--Oregon State University, 1978. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)-Oregon State University, 1978. / Includes bibliographical referenes (leaves 151-162). Also available via the Internet.

Thesis (M.S.)--Oregon State University. / Includes bibliographical references (leaves 77-78). Also available on the World Wide Web.

In this thesis, the results from a geophysical mapping and coring campaign of Lagoa das Furnas are presented. Specific focus is placed on the origin of a subaqueous volcanic cone mapped in the southern part of the lake. Lagoa das Furnas is a crater lake within the Furnas volcanic centre which is located on the island of São Miguel in the Azores archipelago. The Furnas volcanic centre has a long history of earthquakes and volcanic activity. The area is relatively well-studied, except for the lake floor. Therefore, a high resolution geophysical and geological mapping survey was conducted at Lagoa das Furnas. Sidescan sonar was used to map the surface of the lake floor and single beam sonar was used to acquire sub-bottom profiles. In addition to the geophysical mapping, sediment surface sampling and core drilling were carried out followed by geochemical analyses of the retrieved material. The mapped data permitted a characterisation of the floor of Lagoa das Furnas and revealed several volcanic features including fumarole activity and a volcanic cone in the southern part of the lake. In order to unravel the origin of this cone several methods were applied, including analyses of tephra and minerals collected from the cone itself and from nearby deposits of two known eruptions Furnas I and Furnas 1630. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the cone suggest a subaqueous eruption linked to the Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the cone suggests that it is composed of more evolved magma than that of the main Furnas 1630 implying that the lake cone is likely a product of the last eruptional phase. Historical documents reveal three lakes in Furnas valley before the 1630 eruption. Two of these lakes were lost due the eruption and the remaining lake is most likely Lagoa das Furnas and consequently did exist before the 1630 eruption.

No description available.

Thesis (M.S.)-Oregon State University, 1975. / Typescript (photocopy). Includes bibliographical references (leaves 120-127). Also available via the Internet.

Paleoenvironmental investigations establish important baseline knowledge of the natural variability of lake systems, to better understand human impacts on the landscape, and the effects of climate change on water resources. By combining long-term environmental history with investigations into modern land use patterns and climatological events, a wider perspective can be reached that has practical applications in water governance. This thesis presents a case study of Lake Basotu (4.37°S, 35.07°E), a crater lake in the Hanang district of north-central Tanzania, which acts as an important source of freshwater for local people. A three-meter long sediment core from an interior crater of Lake Basotu was investigated using proxy records (diatoms, magnetic parameters, and carbon content) and radiometric dating (14C and 210Pb). The Lake Basotu record was then compared to other sediment-based reconstructions from East Africa and records of historical famines to better place it into the timeline and understanding of regional climate dynamics. This work was extended into modern times (1973–2015) by examining lake extent variations in the Landsat satellite archive. Shoreline boundaries for dry-season images were delineated and lake extent was calculated using GIS techniques. This remote sensing record was compared to climatological patterns, meteorological records, and the history of land-use changes in the surrounding district. As a whole, the Lake Basotu record indicates that major fluctuations in lake level are not abnormal; however, human influence has likely increased the lake’s sensitivity to climatic fluctuations. The timing of historical famines in East Africa were linked to periods of shallow lake conditions in Basotu, and the duration of the most extreme lake level changes correlate to a reversal in the 14C age-depth model. Recent variations in lake extent are likely connected to a mechanized wheat farming program implemented in the district as a foreign aid project in the early 1960s. To support the work done in Basotu, a preliminary investigation of sediment from the nearby Lake Babati was undertaken. Sediment from the two lakes indicates that their geographical location may be in a transition zone towards dryer conditions to the south during the Little Ice Age in East Africa. The results of this thesis support that Lake Basotu is an important location for understanding the potential impacts of climate change and human activity on water resources in this region. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Manuscript.</p>