title: The Fault in our Hill: Characterisation of the Rangitawa Tephra, and insight into tectonic influences at Hillcrest Road

authors: Gibbons, Vittoria

subjects: Tephra

abstract: This study aimed to identify deformation and characterise the Rangitawa Tephra in terms of geomechanical and geochemical properties, and relate these properties to the deformation potential/activity. It was hypothesised there is a fault present in the site at 59 Hillcrest Road, and that the Rangitawa Tephra deforms plastically and accommodates deformation thereby reducing the amount of deformation in the geological units above.  

Field analyses included stratigraphic observations, unit descriptions, structural observations and anomaly identification, sensitivity measurements, and description of soft sediment deformation structures. Laboratory analyses consisted of particle-size, mineralogy, chemistry, and microstructure analyses and geomechanical behaviour identification through Atterberg Limits and Triaxial shear testing. 

Field analyses showed the presence of soft sediment deformation in the form of offset and deformed bedding at the base of the Rangitawa Tephra unit, and in the Hamilton Ash Formation above, along with a significant offset of approximately 6 metres within the cutting at 59 Hillcrest Road. This is inferred to be a normal fault, with the surrounding deformation seismites resulting from seismic triggers in the area along this fault plane. 

Laboratory analyses were used to characterise the Rangitawa Tephra at Hillcrest Road based on geomechanical, chemical, and mineralogical properties indicated the Rangitawa is bimodal extra-fine silt and extra-fine sand with an average of medium silt texture, behaving as a low compressibility silt. The clay mineralogy present as halloysite, dehydrated in Atterberg Limits testing, but hydrated otherwise. Triaxial shear testing identified the Rangitawa Tephra at Hillcrest to be of normally consolidated material, exhibiting ductile-plastic characteristics. The properties indicated during laboratory analyses were used to provide explanations for the deformation structures observed in the exposure at 59 Hillcrest Road. Field analyses along with the laboratory characterisation of the Rangitawa Tephra confirm the presence of a fault plane at the exposure. 


The thesis concludes the Rangitawa Tephra exhibits plastic deformation characteristics, presenting the potential to exhibit cyclic softening. These findings confirm the presence of ductile displacement, and support the soft sediment deformation structures observed at the base of the Rangitawa Tephra, and in the Hamilton Ash formation, are the direct result of paleoseismic influences within the area. It can then be suggested this fault zone may be active (displacement younger than 100 ky.) (GNS, 2017). The ductile plastic characteristics of the Rangitawa Tephra suggests deformation within and above this unit could be present, masked by the atypical displacement features and reduced by the accommodated deformation by the Rangitawa Tephra, suggesting the inferred ages on other faults found within the basin may be much younger than expected.

text: The Fault in our Hill: Characterisation of the Rangitawa Tephra, and insight into tectonic influences at Hillcrest Road This study aimed to identify deformation and characterise the Rangitawa Tephra in terms of geomechanical and geochemical properties, and relate these properties to the deformation potential/activity. It was hypothesised there is a fault present in the site at 59 Hillcrest Road, and that the Rangitawa Tephra deforms plastically and accommodates deformation thereby reducing the amount of deformation in the geological units above.  

Field analyses included stratigraphic observations, unit descriptions, structural observations and anomaly identification, sensitivity measurements, and description of soft sediment deformation structures. Laboratory analyses consisted of particle-size, mineralogy, chemistry, and microstructure analyses and geomechanical behaviour identification through Atterberg Limits and Triaxial shear testing. 

Field analyses showed the presence of soft sediment deformation in the form of offset and deformed bedding at the base of the Rangitawa Tephra unit, and in the Hamilton Ash Formation above, along with a significant offset of approximately 6 metres within the cutting at 59 Hillcrest Road. This is inferred to be a normal fault, with the surrounding deformation seismites resulting from seismic triggers in the area along this fault plane. 

Laboratory analyses were used to characterise the Rangitawa Tephra at Hillcrest Road based on geomechanical, chemical, and mineralogical properties indicated the Rangitawa is bimodal extra-fine silt and extra-fine sand with an average of medium silt texture, behaving as a low compressibility silt. The clay mineralogy present as halloysite, dehydrated in Atterberg Limits testing, but hydrated otherwise. Triaxial shear testing identified the Rangitawa Tephra at Hillcrest to be of normally consolidated material, exhibiting ductile-plastic characteristics. The properties indicated during laboratory analyses were used to provide explanations for the deformation structures observed in the exposure at 59 Hillcrest Road. Field analyses along with the laboratory characterisation of the Rangitawa Tephra confirm the presence of a fault plane at the exposure. 


The thesis concludes the Rangitawa Tephra exhibits plastic deformation characteristics, presenting the potential to exhibit cyclic softening. These findings confirm the presence of ductile displacement, and support the soft sediment deformation structures observed at the base of the Rangitawa Tephra, and in the Hamilton Ash formation, are the direct result of paleoseismic influences within the area. It can then be suggested this fault zone may be active (displacement younger than 100 ky.) (GNS, 2017). The ductile plastic characteristics of the Rangitawa Tephra suggests deformation within and above this unit could be present, masked by the atypical displacement features and reduced by the accommodated deformation by the Rangitawa Tephra, suggesting the inferred ages on other faults found within the basin may be much younger than expected.

year: 2020

title: Average score per metric: an alternative metric aggregation method for assessing wadeable stream health

authors: Collier, Kevin J.

subjects: macroinvertebrate

abstract: Integrating multiple metrics derived from stream macroinvertebrate communities into single scores that reflect ecological condition can bridge the needs of multiple groups using biomonitoring data. Macroinvertebrate metrics from 511 Waikato, New Zealand, stream samples were standardised by their maximum observed value. Metric redundancy and optimisation processes identified three standardised metrics from an initial set of 17 that provided greatest discrimination between reference sites and those influenced by urbanisation or high levels of pastoral development: the richness of Ephemeroptera, Plecoptera and Trichoptera excluding Hydroptilidae (EPT*), % EPT* and the macroinvertebrate community index (MCI). The mean of these standardised metrics was used to calculate the average score per metric (ASPM). Narrative condition bands were developed based on the lower SD of individual metrics for reference samples to distinguish “very high” values, and metric quartiles between this point and a hypothetical worst-case community were used to define “high”, “moderate”, “low”, and “very low” bands. When compared with its component metrics, the ASPM distinguished reference conditions and low–moderate levels of catchment modification and local habitat degradation more accurately than EPT* richness or MCI, and displayed lower temporal variability within reference sites than either EPT* metric. The ASPM was calculated for an independent test data set of urban and reference sites which, respectively, were allocated to low–very low and high–very high narrative condition bands. This analysis suggests that prudent application of the ASPM can provide a parsimonious and effective screening tool for assessing the condition of wadeable streams where more complex methods are not practical.

text: Average score per metric: an alternative metric aggregation method for assessing wadeable stream health Integrating multiple metrics derived from stream macroinvertebrate communities into single scores that reflect ecological condition can bridge the needs of multiple groups using biomonitoring data. Macroinvertebrate metrics from 511 Waikato, New Zealand, stream samples were standardised by their maximum observed value. Metric redundancy and optimisation processes identified three standardised metrics from an initial set of 17 that provided greatest discrimination between reference sites and those influenced by urbanisation or high levels of pastoral development: the richness of Ephemeroptera, Plecoptera and Trichoptera excluding Hydroptilidae (EPT*), % EPT* and the macroinvertebrate community index (MCI). The mean of these standardised metrics was used to calculate the average score per metric (ASPM). Narrative condition bands were developed based on the lower SD of individual metrics for reference samples to distinguish “very high” values, and metric quartiles between this point and a hypothetical worst-case community were used to define “high”, “moderate”, “low”, and “very low” bands. When compared with its component metrics, the ASPM distinguished reference conditions and low–moderate levels of catchment modification and local habitat degradation more accurately than EPT* richness or MCI, and displayed lower temporal variability within reference sites than either EPT* metric. The ASPM was calculated for an independent test data set of urban and reference sites which, respectively, were allocated to low–very low and high–very high narrative condition bands. This analysis suggests that prudent application of the ASPM can provide a parsimonious and effective screening tool for assessing the condition of wadeable streams where more complex methods are not practical.

year: 2008

title: Maori syllabus and the curriculum documents: A critical analysis. Part 1: Tihe Mauri Ora

authors: Crombie, Winifred

subjects: Te reo Māori

abstract: This paper presents, within the context of ongoing debates on syllabus design, a critical analysis of Tihē Mauri Ora, a syllabus document produced by the New Zealand Ministry of Education to support the teaching and learning of the Māori language in schools in New Zealand. It includes a number of suggestions in relation to any future documents prepared with similar intent.

text: Maori syllabus and the curriculum documents: A critical analysis. Part 1: Tihe Mauri Ora This paper presents, within the context of ongoing debates on syllabus design, a critical analysis of Tihē Mauri Ora, a syllabus document produced by the New Zealand Ministry of Education to support the teaching and learning of the Māori language in schools in New Zealand. It includes a number of suggestions in relation to any future documents prepared with similar intent.

year: 2001