title: New insights into the condensed nature and stratigraphic significance of the Late Neogene Ariki Formation, Taranaki Basin

authors: Hansen, Rochelle J.

subjects: Ariki Formation

abstract: The Ariki Formation is a distinctive Late Miocene – Early Pliocene marl facies rich in planktic foraminifera, reaching thicknesses in the range 70 - 109 m in most exploration holes drilled into the Western Platform northwest of Taranaki Peninsula. In Awatea-1 and Mangaa-1 in the Northern Graben, however, there are two marl units separated by the Mangaa “B” Sands. The lower unit has the same upper Tongaporutuan and Kapitean age as the lower part of the marl on the Western Platform, and the upper marl has an Upper Opoitian - Waipipian age, similar to the upper part of the Ariki Formation on the platform. In other holes located on the margins of the graben there can be one thin marly horizon, which usually correlates with the upper marl unit in Awatea-1 and Mangaa-1. 
The presence of two marly units in the Northern Graben, which are probably amalgamated on the western Platform, suggests two periods of late Neogene condensed sedimentation in northern Taranaki Basin arising from siliciclastic sediment starvation, separated by a period of submarine fan accumulation (Mangaa ‘B’ sands) following subsidence of the Northern Graben. We attribute the initial interval of marl accumulation mainly to a marked landward shift in the position of coastal onlap in central and southern Taranaki and in the region east of the Taranaki Fault Zone (southern King Country and northern Wanganui regions), which effectively shut-off the supply of siliciclastic sediment to northern Taranaki Basin, thereby enabling marl to accumulate. The start of accumulation of the upper part of the Ariki Formation and its marly correlatives in and around the Northern Graben, is attributed to a younger (upper Opoitian) landward shift in the position of coastal onlap, this time involving the formation of the Wanganui Basin depocentre and Toru Trough, which trapped the contemporary siliciclastic sediment being supplied from the south. A lower Opoitian phase of progradation between these two phases of retrogradation led to accumulation of the lower part of the Mangaa Formation (Mangaa ’B’ sands), which was limited in its extent to the Northern Graben because bounding normal faults had by then developed sea floor relief precluding mass-emplaced siliciclastic sediment from being deposited on the higher standing Western Platform. The accumulation of Ariki Formation marl in northern Taranaki Basin ended during the mid-Pliocene due to progradation of a thick continental margin wedge (Giant Foresets Formation) across the Northern Graben and Western Platform.

text: New insights into the condensed nature and stratigraphic significance of the Late Neogene Ariki Formation, Taranaki Basin The Ariki Formation is a distinctive Late Miocene – Early Pliocene marl facies rich in planktic foraminifera, reaching thicknesses in the range 70 - 109 m in most exploration holes drilled into the Western Platform northwest of Taranaki Peninsula. In Awatea-1 and Mangaa-1 in the Northern Graben, however, there are two marl units separated by the Mangaa “B” Sands. The lower unit has the same upper Tongaporutuan and Kapitean age as the lower part of the marl on the Western Platform, and the upper marl has an Upper Opoitian - Waipipian age, similar to the upper part of the Ariki Formation on the platform. In other holes located on the margins of the graben there can be one thin marly horizon, which usually correlates with the upper marl unit in Awatea-1 and Mangaa-1. 
The presence of two marly units in the Northern Graben, which are probably amalgamated on the western Platform, suggests two periods of late Neogene condensed sedimentation in northern Taranaki Basin arising from siliciclastic sediment starvation, separated by a period of submarine fan accumulation (Mangaa ‘B’ sands) following subsidence of the Northern Graben. We attribute the initial interval of marl accumulation mainly to a marked landward shift in the position of coastal onlap in central and southern Taranaki and in the region east of the Taranaki Fault Zone (southern King Country and northern Wanganui regions), which effectively shut-off the supply of siliciclastic sediment to northern Taranaki Basin, thereby enabling marl to accumulate. The start of accumulation of the upper part of the Ariki Formation and its marly correlatives in and around the Northern Graben, is attributed to a younger (upper Opoitian) landward shift in the position of coastal onlap, this time involving the formation of the Wanganui Basin depocentre and Toru Trough, which trapped the contemporary siliciclastic sediment being supplied from the south. A lower Opoitian phase of progradation between these two phases of retrogradation led to accumulation of the lower part of the Mangaa Formation (Mangaa ’B’ sands), which was limited in its extent to the Northern Graben because bounding normal faults had by then developed sea floor relief precluding mass-emplaced siliciclastic sediment from being deposited on the higher standing Western Platform. The accumulation of Ariki Formation marl in northern Taranaki Basin ended during the mid-Pliocene due to progradation of a thick continental margin wedge (Giant Foresets Formation) across the Northern Graben and Western Platform.

year: 2008

title: Storm Surges in Tauranga Harbour

authors: Tyler, Michael Jack

abstract: Understanding the potential elevation of extreme sea-levels at the coast is important for management of hazards, and adaptation to climate change. This poses challenges for coastlines around the globe, with current pressure from sea-level rise and predictions for an increase in the frequency of extreme events, storminess and associated storm surge hazards. Therefore present day extreme sea-levels are likely to occur more frequently in the future, reaching higher elevations. The largest storm surge on record in New Zealand was 0.88 m in Tauranga Harbour during Tropical Cyclone Gisele in 1968. This is lower in comparison to the tide which can be up to 2 m, therefore it is important to consider the role of storm tides on extreme sea-levels in New Zealand.

The main aim of this research is to understand how storm conditions amplify the sea-level variations across Tauranga Harbour. This is one of the first studies that aims to understand how storm conditions amplify the sea-level in the upper regions of the Harbour, and therefore affect the hazards in this zone. The peaks over threshold method was applied to sea-level data at four gauges inside the Harbour, and one on the open coast at Moturiki Island. Extreme storm surges were found to be influenced by the morphology of the coastline, and are largest at Omokoroa. Due to relatively short sea-level records, additional techniques using oral histories and photographic evidence provide additional data which can be used to validate results from extreme value analyses. Storm surge is variable depending on the intensity and track of significant storms relative to Tauranga Harbour.

On the 5th January 2018 a sub-tropical storm passing over Tauranga, coincided with king tide conditions, causing significant inundation around Tauranga Harbour. The event produced maximum recorded storm surge of 0.64 m at Hairini, with an estimated average recurrence interval of 100 years at this sea-level gauge. The combination of storm tide and wave run-up was highest around the southern entrance, indicating significant external wave energy entered the Harbour. This event is an important reminder to monitor weather conditions closely during periods of king tide conditions. 

Stepwise regression was also applied to determine the variance in storm surge explained by atmospheric pressure and wind. Atmospheric pressure explains approximately 50% of the variance in storm surges. Wind from the east was found to explain an additional 3 to 15% of the variance, with the most influence at Omokoroa as it experiences large fetches from the east, being located on the north eastern side of the Peninsula. Waves likely explain the remaining variance in storm surges which is supported by findings from historical events in this study, however further research is needed to quantify the effect of waves. The relationship between storm surge frequency and magnitude with the Southern Oscillation Index was investigated at Moturiki, due to the potential for increased coastal hazards during La Niña. No statistically significant relationship was identified, however the results indicate larger, more frequent surges during La Niña. Since 2012, there has been a greater frequency of storm surge events per year exceeding 0.4 m. This may be the result of the Interdecadal Pacific Oscillation which shifted around 2000, and was predicted to increase the storm surge hazard for several decades based on previous research.

The research provides information and data on sea-levels and storm surges which will be useful in the implementation of the King Tides Project in Tauranga Harbour. This is a tool primarily focused on engaging the community with sea-level related information and coastal hazards, which is crucial for increasing awareness and our ability to adapt to coastal hazards.

text: Storm Surges in Tauranga Harbour Understanding the potential elevation of extreme sea-levels at the coast is important for management of hazards, and adaptation to climate change. This poses challenges for coastlines around the globe, with current pressure from sea-level rise and predictions for an increase in the frequency of extreme events, storminess and associated storm surge hazards. Therefore present day extreme sea-levels are likely to occur more frequently in the future, reaching higher elevations. The largest storm surge on record in New Zealand was 0.88 m in Tauranga Harbour during Tropical Cyclone Gisele in 1968. This is lower in comparison to the tide which can be up to 2 m, therefore it is important to consider the role of storm tides on extreme sea-levels in New Zealand.

The main aim of this research is to understand how storm conditions amplify the sea-level variations across Tauranga Harbour. This is one of the first studies that aims to understand how storm conditions amplify the sea-level in the upper regions of the Harbour, and therefore affect the hazards in this zone. The peaks over threshold method was applied to sea-level data at four gauges inside the Harbour, and one on the open coast at Moturiki Island. Extreme storm surges were found to be influenced by the morphology of the coastline, and are largest at Omokoroa. Due to relatively short sea-level records, additional techniques using oral histories and photographic evidence provide additional data which can be used to validate results from extreme value analyses. Storm surge is variable depending on the intensity and track of significant storms relative to Tauranga Harbour.

On the 5th January 2018 a sub-tropical storm passing over Tauranga, coincided with king tide conditions, causing significant inundation around Tauranga Harbour. The event produced maximum recorded storm surge of 0.64 m at Hairini, with an estimated average recurrence interval of 100 years at this sea-level gauge. The combination of storm tide and wave run-up was highest around the southern entrance, indicating significant external wave energy entered the Harbour. This event is an important reminder to monitor weather conditions closely during periods of king tide conditions. 

Stepwise regression was also applied to determine the variance in storm surge explained by atmospheric pressure and wind. Atmospheric pressure explains approximately 50% of the variance in storm surges. Wind from the east was found to explain an additional 3 to 15% of the variance, with the most influence at Omokoroa as it experiences large fetches from the east, being located on the north eastern side of the Peninsula. Waves likely explain the remaining variance in storm surges which is supported by findings from historical events in this study, however further research is needed to quantify the effect of waves. The relationship between storm surge frequency and magnitude with the Southern Oscillation Index was investigated at Moturiki, due to the potential for increased coastal hazards during La Niña. No statistically significant relationship was identified, however the results indicate larger, more frequent surges during La Niña. Since 2012, there has been a greater frequency of storm surge events per year exceeding 0.4 m. This may be the result of the Interdecadal Pacific Oscillation which shifted around 2000, and was predicted to increase the storm surge hazard for several decades based on previous research.

The research provides information and data on sea-levels and storm surges which will be useful in the implementation of the King Tides Project in Tauranga Harbour. This is a tool primarily focused on engaging the community with sea-level related information and coastal hazards, which is crucial for increasing awareness and our ability to adapt to coastal hazards.

year: 2018

title: Te matakite - Te kupu whakaari

authors: Temara, Pou

subjects: Matakite

abstract: Ko te whāinga o tēnei tuhinga poto he matapaki i te matakite me te kupu whakaari, arā, he whakatakoto i tētahi tūāpapa kōrero e mārama ai te kaipānui ki te tikanga o ēnei kaupapa e rua e ai ki tā te Māori i matapaki ai. Otirā, he kōrero tā ngā iwi katoa o te ao mō te matakite me te kupu whakaari, kai tēnā iwi tāna kōrero, kai tēnā iwi tāna. Kāore tēnei tuhinga e rere ki te whakamārama i ā ētahi kōrero, engari mau tonu ki te ao Māori. Mēnā ka whakahua i ngā whakamārama a ētahi atu iwi, e whai ana kia mārama ai te tauira ki tā te Māori i kōrero ai.

text: Te matakite - Te kupu whakaari Ko te whāinga o tēnei tuhinga poto he matapaki i te matakite me te kupu whakaari, arā, he whakatakoto i tētahi tūāpapa kōrero e mārama ai te kaipānui ki te tikanga o ēnei kaupapa e rua e ai ki tā te Māori i matapaki ai. Otirā, he kōrero tā ngā iwi katoa o te ao mō te matakite me te kupu whakaari, kai tēnā iwi tāna kōrero, kai tēnā iwi tāna. Kāore tēnei tuhinga e rere ki te whakamārama i ā ētahi kōrero, engari mau tonu ki te ao Māori. Mēnā ka whakahua i ngā whakamārama a ētahi atu iwi, e whai ana kia mārama ai te tauira ki tā te Māori i kōrero ai.

year: 2016