2,411 research outputs found
Uses of volcanic ash beds in geomorphology
In geomorphology air-fall volcanic ashes possess high value as marker beds. These have proved particularly useful in studies associated with infilling of flood plains, fan building, terrace correlation and chronology, erosion, shoreline and sea level changes, recent tectonics, archaeology and ground surfaces. Ash beds and the community are also discussed
Volcanic ash beds in the Waikato district
This report lies somewhere between the "pathfinder" variety and the completed account for the reason that the results of detailed mapping and identification are still being prepared for publication. For the younger beds less than 36,000 years we now know both the source and the distribution, but for the older ashes commonly referred to as the Hamilton ash, sources are unknown and a knowledge of distribution restricted to the Waikato district. The principal source is the Okataina volcanic centre with Taupo as a subsidiary (Healy, 1964; Thompson, 1964 :44), and on this information, current mapping into the Waikato district proceeds from the east.
Under the circumstances of partly completed work it seems prudent to discuss relevant ash beds already known (Vucetich and Pullar, 1963:65-6; 1964:45-6) to introduce briefly current work by the same authors and by W. T. Ward, and then to relate all of this to previous work portrayed in a soil-forming ash shower map by Taylor (1953)
Chronology of fans and terraces in the Galatea Basin
Air-borne volcanic ash beds are used to date fans and terraces in the Galatea Basin and to outline the depositional history of this part of the Rangitaiki Valley. The basin is interpreted as a fault-angle depression formed by a downwarped sheet of ignimbrite and an upthrusted block of greywacke which forms the Ikawhenua Range. It is from this range that much of the detritus has been derived to fill the basin, deposited mainly in the form of fans and terraces. The larger fans cover a wide area and their surfaces are older than the Rotoma eruption of c. 8000 years B.P. The widespread occurrence of these fans indicates a major erosion interval between c. 11,000 and c. 8,000 years ago. The younger fans are distributed in a particular order with fans of the Pre-Taupo surface north of the Horomanga Stream and those of the Pre- and Post-Kaharoa surfaces south of the same stream. This ordered distribution of the younger fans suggests a climatic control of fan building.
Aggradation and degradation phases in the Rangitaiki and Whirinaki Rivers have formed a pronounced meander trough containing terraces of the Pre-Taupo, Pre-Kaharoa, and Post-Kaharoa surfaces. The terrace of the Pre-Kaharoa surface, largely of Taupo Pumice alluvium, is the most common. Degradation, however, is controlled by a local base level at the ignimbrite rapids on the Rangitaiki River just north of the Galatea Basin
Regression trend lines of ridges and swales on the emergent beach at Gisborne, New Zealand
The emergent sand-beach system at Gisborne consists of six recognisable groups of ridges and swales. It is about three miles wide and four miles long and rises gradually from 15ft above sea level at the coast to 40ft inland. From time to time the emergent beach has been mantled with air-borne volcanic ash including ash beds of the Waimihia Lapilli, Taupo Sub-group Members 9 - 13, Taupo Pumice, and Kaharoa Ash Formations. As the dates of these eruptions are known, the times of formation of the groups of beach ridges and wales have been determined as follows:
Group 1: c. 9000 B.C. - c. 1400 B.C.
Group 2: c. 1400 B.C. - (?) 850 B.C.
Group 3: (?) 850 B.C. - c. A.D. 131
Group 4: c. A.D. 131 - c. A.D. 1020
Group 5: c. A.D. 1020 - c. A.D. 1650
Group 6: c. A.D. 1650 - A.D. 1956
Evidence of recent earth movements has been noted in ridges and swales of Group 1, and of possible movements in those of Group 3. Changes in sea level could not be established and were taken from Wellman and Schofield. No attempt was made to distinguish directly wind-blown sand from wave-deposited sand; instead, a shell layer (assumed to be associated with the intertidal strand) was used as a marker bed to indicate the approximate sea level at the time when the shells were deposited.
Elevations of ridges and swales in each group were measured on a 15,000ft transect across the beach system. Then, overall linear and quadratic regressions as well as linear regressions for each group separately were computed. For both of the overall linear and quadratic regressions the trend lines show a fall seaward, but the separate trend lines for each group are as follows:
Group 1: Highly significant seaward decline.
Groups 2 and 3 combined: Very highly significant seaward decline.
Group 4: Highly significant seaward incline.
Groups 5 and 6 combined: No significant change.
The departure of the regression trend lines within Groups 1 to 6 from the overall linear and quadratic trend lines suggests that the trends of elevation across the emergent beach at Gisborne should be regarded more as a series of discontinuous trends rather than as one overall continuous trend of seaward decline. Though the overall trend of declining elevation is seaward, the corresponding fall in sea level is likely to be more apparent than real because of compounding of fall in sea level with earth movements
Annotated bibliography of central North Island volcanic ash stratigraphy
Prior to 1929 many observations had been published giving brief accounts of the volcanic ash deposits in various parts of the North Island but no detailed investigations were undertaken. With the incidence of Bush Sickness in the Central North Island mapping of the "ash soils" was undertaken as part of the investigations into the cause of this disease. The work done at this time was the beginning of our present understanding of ash stratigraphy. In this bibliography only papers relevant to the Central North Island ash-showers have been mentioned
The age of quaternary surfaces at Waihi Beach
The Waihi Beach surfaces were originally mapped and correlated with European surfaces of similar altitude by Kear and Waterhouse (1961). Exposures along the edges of the surfaces indicate that they are covered with volcanic ashes, the younger of which are of known age. It is the sub-ash surface which should be used for height correlations, and it is the most seaward ash-covered part of the surface which is preferred as the reference point for altitude studies. The heights of the surfaces may not correlate with positions of sea-level at the ages indicated by the ash beds
Incorporating level set methods in Geographical Information Systems (GIS) for land-surface process modeling
Land-surface processes include a broad class of models that operate at a landscape scale. Current modelling approaches tend to be specialised towards one type of process, yet it is the interaction of processes that is increasing seen as important to obtain a more integrated approach to land management. This paper presents a technique and a tool that may be applied generically to landscape processes. The technique tracks moving interfaces across landscapes for processes such as water flow, biochemical diffusion, and plant dispersal. Its theoretical development applies a Lagrangian approach to motion over a Eulerian grid space by tracking quantities across a landscape as an evolving front. An algorithm for this technique, called level set method, is implemented in a geographical information system (GIS). It fits with a field data model in GIS and is implemented as operators in map algebra. The paper describes an implementation of the level set methods in a map algebra programming language, called MapScript, and gives example program scripts for applications in ecology and hydrology
Sulphasalazine in Rheumatoid Arthritis
Recent open studies of sulphasalazine have suggested that it may have "second line" antirheumatic activity. Previous experience with sulphasalazine in the treatment of inflammatory bowel disease has also suggested that it may be less toxic than the commonly used second line agents. In addition, the complex pharmacology of sulphasalazine may allow manipulation of a number of variables to improve the efficacy:toxicity ratio and may also shed some more light on the rheumatoid disease process. I, therefore, decided to investigate further the use of this drug in rheumatoid arthritis. My specific aims were: (1) to investigate by means of a placebo controlled trial the efficacy of sulphasalazine; (2) to document its toxicity and relate toxicity and efficacy to a number of variables; (3) to investigate its single dose pharmacokinetics; (4) to define its optimal clinical use; (5) to examine for an effect on free radical scavengers as a potential mode of action; (6) to identify its active therapeutic moiety
- …