title: Geology, History and Stratigraphy of Hydrothermal Eruptions in the Rotorua Geothermal Field

authors: Cody, Ashley Douglas

subjects: Geothermal Hydrothermal eruptions Rotorua

abstract: The study area is the Rotorua geothermal field (RGF), which is located in the southern end of the Rotorua caldera. Distribution of surface geothermal activity, hydrothermal eruption (HE) deposits and craters have been mapped. HE deposits formed in geological, historical and modern times were studied to record and describe their distribution, composition, petrography, lithology and stratigraphy.

Locations of all identified HE sites in the RGF have been plotted and shown on accompanying maps. At Ohinemutu and Sulphur Bay, HE breccias have been preserved only where deposits were subsequently silicified by hot spring outflows. At Whakarewarewa two HE breccias outcrop over about 0.5 km² and are up to 23 m thick. Study of stratigraphic relationships with tephras of known ages has determined one as Holocene (c. 20 ka) and one of Late Pleistocene age (c. 65 ka).

Four HE breccias were studied in detail. The mineral composition, physical description, field characteristics and spatial distribution of HE breccias are described and mapped. Clasts and matrix were examined by XRD analyses of whole (67) and clay fraction separates (16). Silica crystallinity indices (14) were determined by XRD to identify devitrification rates of opaline mineral species. The petrography of 67 breccia clasts and matrix samples were studied, and polished sections showed the only sulphide to be pyrite. Geothermal alteration of all prehistorical HE deposits was of advanced argillic to argillic and one modern day deposit was of sub propylitic epithermal alteration.

Study of a HE deposit formed in Kuirau Park on 26 January 2001 allowed properties and mineral composition to be examined and recorded before rapid oxidation and weathering destroyed its physical and mineral composition. Study of this and other twentieth century HE events confirms that these rapidly decompose to leave little or no recognisable deposit in the geological record.

Descriptions and all known historical records of HEs in the RGF have been collated to provide a comprehensive inventory of maps and appendices of these events. This information will greatly assist statutory authorities with mitigation of risk to lives and property from geothermal hazards as well as aid appropriate land use and emergency services planning.

Hydrothermal eruptions are ongoing in the RGF through time and produce craters 2 - 110m diameter with erupted deposit volumes of 1 - 500,000 m³ that have distributed over <5 m² to >0.5 km². These have occurred throughout at least Late Pleistocene to Holocene times and appear to have been triggered by such events as volcanic eruptions from the adjacent Okataina Volcanic Centre and related abrupt changes to the waterlevels of Lake Rotorua. Frequency and spatial distribution of HEs in historical times suggest human interference with the geothermal system is also a significant influence.

This study has brought together all records of known hydrothermal eruptions and other unusual geothermal disturbances in the Rotorua geothermal field. The information has plotted into GIS for use by statutory authorities and others. Two prehistorical HE deposits in Rotorua city have also been recognised and described for the first time, together with identification of their likely vent locations and possible eruption initiating events.

text: Geology, History and Stratigraphy of Hydrothermal Eruptions in the Rotorua Geothermal Field The study area is the Rotorua geothermal field (RGF), which is located in the southern end of the Rotorua caldera. Distribution of surface geothermal activity, hydrothermal eruption (HE) deposits and craters have been mapped. HE deposits formed in geological, historical and modern times were studied to record and describe their distribution, composition, petrography, lithology and stratigraphy.

Locations of all identified HE sites in the RGF have been plotted and shown on accompanying maps. At Ohinemutu and Sulphur Bay, HE breccias have been preserved only where deposits were subsequently silicified by hot spring outflows. At Whakarewarewa two HE breccias outcrop over about 0.5 km² and are up to 23 m thick. Study of stratigraphic relationships with tephras of known ages has determined one as Holocene (c. 20 ka) and one of Late Pleistocene age (c. 65 ka).

Four HE breccias were studied in detail. The mineral composition, physical description, field characteristics and spatial distribution of HE breccias are described and mapped. Clasts and matrix were examined by XRD analyses of whole (67) and clay fraction separates (16). Silica crystallinity indices (14) were determined by XRD to identify devitrification rates of opaline mineral species. The petrography of 67 breccia clasts and matrix samples were studied, and polished sections showed the only sulphide to be pyrite. Geothermal alteration of all prehistorical HE deposits was of advanced argillic to argillic and one modern day deposit was of sub propylitic epithermal alteration.

Study of a HE deposit formed in Kuirau Park on 26 January 2001 allowed properties and mineral composition to be examined and recorded before rapid oxidation and weathering destroyed its physical and mineral composition. Study of this and other twentieth century HE events confirms that these rapidly decompose to leave little or no recognisable deposit in the geological record.

Descriptions and all known historical records of HEs in the RGF have been collated to provide a comprehensive inventory of maps and appendices of these events. This information will greatly assist statutory authorities with mitigation of risk to lives and property from geothermal hazards as well as aid appropriate land use and emergency services planning.

Hydrothermal eruptions are ongoing in the RGF through time and produce craters 2 - 110m diameter with erupted deposit volumes of 1 - 500,000 m³ that have distributed over <5 m² to >0.5 km². These have occurred throughout at least Late Pleistocene to Holocene times and appear to have been triggered by such events as volcanic eruptions from the adjacent Okataina Volcanic Centre and related abrupt changes to the waterlevels of Lake Rotorua. Frequency and spatial distribution of HEs in historical times suggest human interference with the geothermal system is also a significant influence.

This study has brought together all records of known hydrothermal eruptions and other unusual geothermal disturbances in the Rotorua geothermal field. The information has plotted into GIS for use by statutory authorities and others. Two prehistorical HE deposits in Rotorua city have also been recognised and described for the first time, together with identification of their likely vent locations and possible eruption initiating events.

year: 2003

title: Facilitating reflective and collaborative learning in EAP

authors: Fester, Anthea Marcelle

abstract: The research in focus involved a pilot study of the use of ePortfolios in an undergraduate third year English for Academic Purposes (EAP) course at a University in New Zealand. The overarching aim of the research was to evaluate the use of the ePortfolio in facilitating integrated learning, reflection and collaboration in an EAP context.

text: Facilitating reflective and collaborative learning in EAP The research in focus involved a pilot study of the use of ePortfolios in an undergraduate third year English for Academic Purposes (EAP) course at a University in New Zealand. The overarching aim of the research was to evaluate the use of the ePortfolio in facilitating integrated learning, reflection and collaboration in an EAP context.

year: 2018

title: Wāhine Māori engagement with literacies

authors: Masters-Awatere, Bridgette

subjects: Literacy

abstract: Wāhine Māori engagement with literacies (2023) is a case study report in collaboration with Te Whakaruruhau. It has been undertaken as part of a larger project, The expression, experience and transcendence of low skills in Aotearoa New Zealand (2019–2024), the aim of which is to provide policy recommendations to improve life-course trajectories and socio-economic outcomes for adults with low literacy and numeracy skills in Aotearoa New Zealand. Broadly speaking, Wāhine Māori engagement with literacy examines the framing and application of literacy measures in contemporary New Zealand culture. More specifically, it is about the lives and learning of wāhine (women) Māori (the indigenous peoples of Aotearoa New Zealand) within that culture and their attitudes towards, and complex relationships with, literacy as it is defined in their own lives and in the current setting. The study aims for a holistic understanding of lived literacies in driving the development of educational policies by public institutions and private groups. Reframing literacy as literacies is posited as a means to empower marginalised groups and to challenge the dominance of the Eurocentric education paradigm. Formal learning in English-language schools cannot be the extent of national literacy standards as it disregards Māori epistemological and ontological realities and can discount wāhine, many of whom may prioritise other modes of literacy. Centring their perspectives will bring about a more culturally inclusive future, one that makes space for the development of emotional and cultural literacies—as well as other forms such as digital, media, visual, financial, and health literacies—alongside the conventional version of literacy that has a monopoly in the present system.

text: Wāhine Māori engagement with literacies Wāhine Māori engagement with literacies (2023) is a case study report in collaboration with Te Whakaruruhau. It has been undertaken as part of a larger project, The expression, experience and transcendence of low skills in Aotearoa New Zealand (2019–2024), the aim of which is to provide policy recommendations to improve life-course trajectories and socio-economic outcomes for adults with low literacy and numeracy skills in Aotearoa New Zealand. Broadly speaking, Wāhine Māori engagement with literacy examines the framing and application of literacy measures in contemporary New Zealand culture. More specifically, it is about the lives and learning of wāhine (women) Māori (the indigenous peoples of Aotearoa New Zealand) within that culture and their attitudes towards, and complex relationships with, literacy as it is defined in their own lives and in the current setting. The study aims for a holistic understanding of lived literacies in driving the development of educational policies by public institutions and private groups. Reframing literacy as literacies is posited as a means to empower marginalised groups and to challenge the dominance of the Eurocentric education paradigm. Formal learning in English-language schools cannot be the extent of national literacy standards as it disregards Māori epistemological and ontological realities and can discount wāhine, many of whom may prioritise other modes of literacy. Centring their perspectives will bring about a more culturally inclusive future, one that makes space for the development of emotional and cultural literacies—as well as other forms such as digital, media, visual, financial, and health literacies—alongside the conventional version of literacy that has a monopoly in the present system.

year: 2023-09-28