title: Volcanic geology and hydrothermal alteration of the Onemana Area, Eastern Coromandel Peninsula

authors: Aldrich, Sean Mark

subjects: Volcanic Geology

abstract: The Onemana Peninsula is located on the eastern side of the Coromandel Peninsula north of the township of Whangamata. This study investigates the volcanology, structure and hydrothermal alteration of the northern half of the Onemana Peninsula. The study area is dominated by rhyolite domes and lava flows, with minor andesite lavas, rhyolite pyroclastics and lake sediments. The central region is extensively hydrothermally altered, with high levels of the original system preserved including hydrothermal eruption breccias and sinters.

The Onemana area is dominated by three rhyolite dome complexes: Pohakahaka, Pokohino, and Wharekawa. The Pohakahaka Dome Complex in the south of the study area consists of pyroxene rhyolite domes, lavas and autoclastic breccias. The Pokohino Dome Complex in the central region of the study area consists of biotite rhyolite domes, lavas and autoclastic breccias. Lavas appear to have erupted as coulees and have flowed in a SE direction from a NE-trending ridge. The Wharekawa Dome Complex and Eastern Flows are dominated by biotite rhyolites. Pyroclastic and epiclastic material is overlain by rhyolite lavas in coastal sections north of Pokohino Beach, suggesting explosive activity preceded the eruption of some lavas. Some Eastern Flow lavas have flowed into water and produced a hyaloclastite in the north of the area. The deposition of the Glassy Dome Pyroclastics is thought to have resulted from the collapse of a rhyolite dome. Andesite lavas occur in the west of the study area, and their compositions suggest that they are related to the McBeths Andesite which outcrops 6 km to the NW. A hornblende-biotite ignimbrite is exposed in the north of the area, and is thought to have been erupted from outside the area. Thick lake sediments occur between the Pokohino and Wharekawa dome complexes and infill a graben structure. A hydrothermal eruption breccia resulting from over-pressuring of a geothermal system overlies the lake sediments. 

The structure of the area is dominated by NW, N, and NE striking faults, and minor EW striking faults. The local structure plays an important role in controlling the locations of volcanism and hydrothermal activity. Older N-striking structures appear to have controlled vent locations for the pyroxene rhyolites, while NE-striking structures have controlled the location the biotite rhyolites and hydrothermal alteration. Mineralised structures are controlled by NW and N striking faults between the NE striking Whitipirorua and Pokohino Faults.

XRF analysis of selected volcanic rocks from Onemana show the area to be dominated by medium-K to high-K rhyolites (75-78 wt% SiO₂), with minor andesite (56-58 wt% SiO₂). On the basis of Zr abundance the rhyolites can be divided into high Zr (pyroxene rhyolites) and low Zr (biotite rhyolites, Glassy Dome Rhyolite). The rhyolites are thought to be closely associated with partial melting of the continental crust in a rifting environment.

Pervasive to weak alteration occurs within a NE-trending corridor bounded by the Whitipirorua and Pokohino Faults. There are two main alteration types in the area which represent different hydrothermal environments: alkaline and acid alteration. Alkaline alteration consists of an inner core of quartz silicification, surrounded by quartz+ K-feldspar alteration, which grades out into epidote and weak clay alteration assemblages. Zeolites also occur as an overprinting alteration assemblage. Acid alteration consists of pervasive kaolinite alteration, with small areas of quartz + illite/smectite ± pyrophyllite alteration and opaline quartz silicification.

The Onemana area shows many volcanic and hydrothermal features that are typical of caldera settings and are comparable with the rhyolite volcanic centres in the TVZ. It is suggested that the rhyolitic volcanism at Onemana resulted from late stage volcanism along the ring fracture of a large caldera structure.

text: Volcanic geology and hydrothermal alteration of the Onemana Area, Eastern Coromandel Peninsula The Onemana Peninsula is located on the eastern side of the Coromandel Peninsula north of the township of Whangamata. This study investigates the volcanology, structure and hydrothermal alteration of the northern half of the Onemana Peninsula. The study area is dominated by rhyolite domes and lava flows, with minor andesite lavas, rhyolite pyroclastics and lake sediments. The central region is extensively hydrothermally altered, with high levels of the original system preserved including hydrothermal eruption breccias and sinters.

The Onemana area is dominated by three rhyolite dome complexes: Pohakahaka, Pokohino, and Wharekawa. The Pohakahaka Dome Complex in the south of the study area consists of pyroxene rhyolite domes, lavas and autoclastic breccias. The Pokohino Dome Complex in the central region of the study area consists of biotite rhyolite domes, lavas and autoclastic breccias. Lavas appear to have erupted as coulees and have flowed in a SE direction from a NE-trending ridge. The Wharekawa Dome Complex and Eastern Flows are dominated by biotite rhyolites. Pyroclastic and epiclastic material is overlain by rhyolite lavas in coastal sections north of Pokohino Beach, suggesting explosive activity preceded the eruption of some lavas. Some Eastern Flow lavas have flowed into water and produced a hyaloclastite in the north of the area. The deposition of the Glassy Dome Pyroclastics is thought to have resulted from the collapse of a rhyolite dome. Andesite lavas occur in the west of the study area, and their compositions suggest that they are related to the McBeths Andesite which outcrops 6 km to the NW. A hornblende-biotite ignimbrite is exposed in the north of the area, and is thought to have been erupted from outside the area. Thick lake sediments occur between the Pokohino and Wharekawa dome complexes and infill a graben structure. A hydrothermal eruption breccia resulting from over-pressuring of a geothermal system overlies the lake sediments. 

The structure of the area is dominated by NW, N, and NE striking faults, and minor EW striking faults. The local structure plays an important role in controlling the locations of volcanism and hydrothermal activity. Older N-striking structures appear to have controlled vent locations for the pyroxene rhyolites, while NE-striking structures have controlled the location the biotite rhyolites and hydrothermal alteration. Mineralised structures are controlled by NW and N striking faults between the NE striking Whitipirorua and Pokohino Faults.

XRF analysis of selected volcanic rocks from Onemana show the area to be dominated by medium-K to high-K rhyolites (75-78 wt% SiO₂), with minor andesite (56-58 wt% SiO₂). On the basis of Zr abundance the rhyolites can be divided into high Zr (pyroxene rhyolites) and low Zr (biotite rhyolites, Glassy Dome Rhyolite). The rhyolites are thought to be closely associated with partial melting of the continental crust in a rifting environment.

Pervasive to weak alteration occurs within a NE-trending corridor bounded by the Whitipirorua and Pokohino Faults. There are two main alteration types in the area which represent different hydrothermal environments: alkaline and acid alteration. Alkaline alteration consists of an inner core of quartz silicification, surrounded by quartz+ K-feldspar alteration, which grades out into epidote and weak clay alteration assemblages. Zeolites also occur as an overprinting alteration assemblage. Acid alteration consists of pervasive kaolinite alteration, with small areas of quartz + illite/smectite ± pyrophyllite alteration and opaline quartz silicification.

The Onemana area shows many volcanic and hydrothermal features that are typical of caldera settings and are comparable with the rhyolite volcanic centres in the TVZ. It is suggested that the rhyolitic volcanism at Onemana resulted from late stage volcanism along the ring fracture of a large caldera structure.

year: 1995

title: Feelings of home and belonging amongst Bhutanese women and girls with refugee backgrounds who live in New Zealand

authors: Basnet, Sunita

subjects: New Zealand

abstract: This thesis focuses on the everyday home geographies of Bhutanese women and girls with refugee backgrounds in Aotearoa New Zealand. It examines feelings of being at home and belonging for 37 resettled Bhutanese women and girls, and eight men, aged between 12 and 85 years, all living under the third-country resettlement programme in Auckland, Christchurch, Nelson and Palmerston North. Three key informants, who assist with resettlement, are also included in this research. It is argued that everyday experiences of home and belonging are embodied, emotional, and contradictory for Bhutanese women and girls.

Feminist scholarship on gendered feelings of belonging and home informs the framework of the research. Qualitative performative methods are used, comprising 40 semi-structured in-depth interviews; five photo-elicitations; and seven cooking sessions with Bhutanese women. A focus group of five girls aged from 12 to 16 years was also involved in the study. In addition, I adopted a new approach called ‘accidental ethnography’, which comprised stayovers, participant sensing, and cooking sessions in the field. The data gathered was analysed using thematic and discourse analytical approaches. 

My findings are organised into three central themes that relate to belonging and home: bodies; households; and communities. First, I pay attention to the corporeal practices of resettled Bhutanese women and girls in everyday life. Clothing, jewellery, norms, values, language and traditions can enable belonging and feeling at home but they can also generate feelings of discomfort, segregation and being outsiders when two extreme cultures confront each other. Second, I focus on day-to-day activities within households. Creating a familiar environment within households, including being with family, having backyard gardens, consuming culturally appropriate food, maintaining one’s religion and having a sturdy house with meaningful material objects, enable resettled Bhutanese to accept their new country as home. Third, my study shows that a sense of community can enable or hinder participants’ feelings of belonging in New Zealand. Living in smaller cities, being able to exercise and observe Bhutanese traditions, living longer in New Zealand, developing satisfaction with the neighbourhood and feeling safe are all factors that play an important role in forming feelings of community for resettled Bhutanese women and girls.

Feelings of belonging and a sense of being at home are about maintaining, reinforcing and negotiating cultural and gendered identities in New Zealand. This study responds to the lack of critical attention paid to the relationship between home and belonging for resettled Bhutanese women and girls. Considering everyday practices encourages a more critical understanding of belonging and home for women and girls with refugee backgrounds.

text: Feelings of home and belonging amongst Bhutanese women and girls with refugee backgrounds who live in New Zealand This thesis focuses on the everyday home geographies of Bhutanese women and girls with refugee backgrounds in Aotearoa New Zealand. It examines feelings of being at home and belonging for 37 resettled Bhutanese women and girls, and eight men, aged between 12 and 85 years, all living under the third-country resettlement programme in Auckland, Christchurch, Nelson and Palmerston North. Three key informants, who assist with resettlement, are also included in this research. It is argued that everyday experiences of home and belonging are embodied, emotional, and contradictory for Bhutanese women and girls.

Feminist scholarship on gendered feelings of belonging and home informs the framework of the research. Qualitative performative methods are used, comprising 40 semi-structured in-depth interviews; five photo-elicitations; and seven cooking sessions with Bhutanese women. A focus group of five girls aged from 12 to 16 years was also involved in the study. In addition, I adopted a new approach called ‘accidental ethnography’, which comprised stayovers, participant sensing, and cooking sessions in the field. The data gathered was analysed using thematic and discourse analytical approaches. 

My findings are organised into three central themes that relate to belonging and home: bodies; households; and communities. First, I pay attention to the corporeal practices of resettled Bhutanese women and girls in everyday life. Clothing, jewellery, norms, values, language and traditions can enable belonging and feeling at home but they can also generate feelings of discomfort, segregation and being outsiders when two extreme cultures confront each other. Second, I focus on day-to-day activities within households. Creating a familiar environment within households, including being with family, having backyard gardens, consuming culturally appropriate food, maintaining one’s religion and having a sturdy house with meaningful material objects, enable resettled Bhutanese to accept their new country as home. Third, my study shows that a sense of community can enable or hinder participants’ feelings of belonging in New Zealand. Living in smaller cities, being able to exercise and observe Bhutanese traditions, living longer in New Zealand, developing satisfaction with the neighbourhood and feeling safe are all factors that play an important role in forming feelings of community for resettled Bhutanese women and girls.

Feelings of belonging and a sense of being at home are about maintaining, reinforcing and negotiating cultural and gendered identities in New Zealand. This study responds to the lack of critical attention paid to the relationship between home and belonging for resettled Bhutanese women and girls. Considering everyday practices encourages a more critical understanding of belonging and home for women and girls with refugee backgrounds.

year: 2018

title: Life history of fluvial and lacustrine land-locked koaro (Galaxias brevipinnis) Günther (Pisces: galaxiidae) in the Tarawera lakes

authors: Young, Kim D.

abstract: Biological diversity in New Zealand has been seriously degraded as a result of human induced disturbances which include the introduction of many exotic species. Freshwater ecosystems have not escaped damage, with the introduction of primarily sports fish suspected to be a significant contributing factor in diminished native biological freshwater values. This is reflected by range and population reductions of several native fish species. 

One of these species is koaro (Galaxias brevipinnis), for which abundance in land-locked populations in the central North Island lakes has significantly declined. Koaro were once abundant in these lakes, and pre-European harvest in both its juvenile (whitebait) and adult (kokopu) form, comprised an important food resource for inland Maori. Since the introduction of recreational trout species to these lakes in the late 1880s, followed by the introduction of common smelt (Retropinna retropinna) in the early 1900s, the abundance of koaro has dramatically declined to the extent that, in these lakes, the species is now considered rare. 

To date, the interactions between recreational trout species, common smelt, and koaro populations have not been established, and the life-history of land-locked koaro is not fully understood. In particular, the extent of movement between lake and stream habitats remains unclear. However, a collaborative project between the indigenous people of the Rotorua Lakes (Te Arawa) and the Department of Conservation to restore a koaro population in one Rotorua lake, has driven a need to gain a better understanding of the biology and ecology of land-locked koaro. This includes identifying threats to important life-history stages and understanding the role of tributary streams.

During July 1999 to February 2001, lacustrine and fluvial koaro were studied in Lake Tarawera and Lake Okareka and their tributary streams. Both lakes are part of the Tarawera lakes group, a subgroup of the Rotorua lakes situated in the central North Island. Fyke netting was used to sample lacustrine koaro on a monthly basis from January 2000 to February 2001, and seasonal two-pass reduction electric fishing at five sites in the tributary streams took place in April, July and November 2000 and February 2001. All fish larger than 70 mm total length were tagged with a passive implant transponder. Spawning season and location, together with size and growth of lake and stream fish were determined. Movement of lake fish within the littoral zone was also investigated. 

The study found that lake and stream koaro may belong to two sub-populations indicated by differences in size, growth rate, spawning time and locality, and return of lake and stream koaro to natal habitats. The life-history of stream koaro has remained similar to that of its diadromous counterparts. Stream fish were found to spawn and hatch in stream environs, rear as larvae in the lake environs, and return to tributary streams as juvenile fish. Lake fish by contrast, most likely spawn in the lake itself, and results suggest that no juvenile migration of lake spawned fish to tributary streams occurs. Consequently, it was concluded that tributary streams may play little role in the life-history of lacustrine koaro.

Abundance of lacustrine koaro in both Lake Tarawera and Lake Okareka was low in comparison to lakes where trout species or common smelt are absent, and abundance of post-whitebait koaro (greater than 45 mm total length coloured and patterned) in both tributary streams studied was also low where rainbow trout (Oncorhynchus mykiss) were proportionally present in greater abundance. Important life-history stages were found to be subject to competition and predation by a combination of rainbow trout and common smelt in both lakes and streams.

Given the above, restoration programmes for land-locked koaro will need to be undertaken at the population level to enhance the survival of larval and juvenile life-history stages. This will need to occur at an ecosystem scale, and include the management of the combined effects of trout and common smelt in both lake and respective tributary stream environs.

text: Life history of fluvial and lacustrine land-locked koaro (Galaxias brevipinnis) Günther (Pisces: galaxiidae) in the Tarawera lakes Biological diversity in New Zealand has been seriously degraded as a result of human induced disturbances which include the introduction of many exotic species. Freshwater ecosystems have not escaped damage, with the introduction of primarily sports fish suspected to be a significant contributing factor in diminished native biological freshwater values. This is reflected by range and population reductions of several native fish species. 

One of these species is koaro (Galaxias brevipinnis), for which abundance in land-locked populations in the central North Island lakes has significantly declined. Koaro were once abundant in these lakes, and pre-European harvest in both its juvenile (whitebait) and adult (kokopu) form, comprised an important food resource for inland Maori. Since the introduction of recreational trout species to these lakes in the late 1880s, followed by the introduction of common smelt (Retropinna retropinna) in the early 1900s, the abundance of koaro has dramatically declined to the extent that, in these lakes, the species is now considered rare. 

To date, the interactions between recreational trout species, common smelt, and koaro populations have not been established, and the life-history of land-locked koaro is not fully understood. In particular, the extent of movement between lake and stream habitats remains unclear. However, a collaborative project between the indigenous people of the Rotorua Lakes (Te Arawa) and the Department of Conservation to restore a koaro population in one Rotorua lake, has driven a need to gain a better understanding of the biology and ecology of land-locked koaro. This includes identifying threats to important life-history stages and understanding the role of tributary streams.

During July 1999 to February 2001, lacustrine and fluvial koaro were studied in Lake Tarawera and Lake Okareka and their tributary streams. Both lakes are part of the Tarawera lakes group, a subgroup of the Rotorua lakes situated in the central North Island. Fyke netting was used to sample lacustrine koaro on a monthly basis from January 2000 to February 2001, and seasonal two-pass reduction electric fishing at five sites in the tributary streams took place in April, July and November 2000 and February 2001. All fish larger than 70 mm total length were tagged with a passive implant transponder. Spawning season and location, together with size and growth of lake and stream fish were determined. Movement of lake fish within the littoral zone was also investigated. 

The study found that lake and stream koaro may belong to two sub-populations indicated by differences in size, growth rate, spawning time and locality, and return of lake and stream koaro to natal habitats. The life-history of stream koaro has remained similar to that of its diadromous counterparts. Stream fish were found to spawn and hatch in stream environs, rear as larvae in the lake environs, and return to tributary streams as juvenile fish. Lake fish by contrast, most likely spawn in the lake itself, and results suggest that no juvenile migration of lake spawned fish to tributary streams occurs. Consequently, it was concluded that tributary streams may play little role in the life-history of lacustrine koaro.

Abundance of lacustrine koaro in both Lake Tarawera and Lake Okareka was low in comparison to lakes where trout species or common smelt are absent, and abundance of post-whitebait koaro (greater than 45 mm total length coloured and patterned) in both tributary streams studied was also low where rainbow trout (Oncorhynchus mykiss) were proportionally present in greater abundance. Important life-history stages were found to be subject to competition and predation by a combination of rainbow trout and common smelt in both lakes and streams.

Given the above, restoration programmes for land-locked koaro will need to be undertaken at the population level to enhance the survival of larval and juvenile life-history stages. This will need to occur at an ecosystem scale, and include the management of the combined effects of trout and common smelt in both lake and respective tributary stream environs.

year: 2002