title: The nature and dynamics of the Rotorua eruptive episode, Okataina Volcanic Centre, Taupo Volcanic Zone

authors: Kilgour, Geoff

subjects: Volcanic hazard analysis

abstract: The 15.7 cal yrs B.P. Rotorua eruptive episode is the latest expression of western Okataina volcanism. Okataina is one of the world's most active rhyolitic volcanoes and this eruptive episode provides an ideal opportunity to examine the nature, dynamics and impacts of a large magnitude explosive eruption from this volcanic centre.

This re-investigation of the Rotorua eruptive episode has lead to the grouping of the deposits into two distinct phases of eruption. The Rotorua Tephra and Eastern Dome (previously thought to be Te Rere-related) are termed 'Rotorua A' phase. Trig 7693 andMiddle domes (previously linked to the source of the Rotorua Tephra) have been grouped with the Upper Rotorua Tephra into the. 'Rotorua B' phase. These groupings are predominantly based on mineralogy and geochemistry on samples of pyroclastic and dome deposits.

The eruptive sequence began with a small initial ash without a basalt trigger, followed soon after by a plinian fall deposit (1.62 km³) directed to the NW. Dome growth ensued (Eastern dome), creating an extensive rhyolite dome (0.72 km³) in the Okareka Embayment. Soon after Eastern dome growth (based on the absence of paleosol development) the Rotorua B phase was initiated. This phase of predominant effusive dome growth lead to the construction of the coalesced Trig 7693 and Middle domes. Periodic vulcanian explosions and dome collapses lead to the localised dispersal to the S and E, of pyroclastic density currents and fall.

A new age of 12941 ± 75 ¹⁴C years BP was obtained from charcoal in a surge deposit at a proximal site. This results in a revised age for the Rotorua eruption of 15 700 cal yrs BP. The eruption duration is estimated to exceed 15 yrs, based on a total dome volume of 1.37 km³, assuming a growth rate of 3 m ³/s.

To the NW, the Rotorua A plinian deposit (Ap-1 to Ap-10 sub units) is overall normally graded, however cm-scale bedding is evident throughout the deposit. The grain size ranges from a block-sized, basal sub unit to a medium ash, upper. The plinian tephra is biotite-poor compared to the distinct Rotorua B deposits (previously 'Upper Rotorua Tephra'), which is biotite-rich.

Whole rock geochemistry on the Rotorua A pyroclastics, forms an apparent trend, suggesting the magma supplying the explosive phase was compositional zoned prior to eruption and was subsequently disrupted immediately prior to or during eruption. The Rotorua A and B phases plot as distinct clusters in all binary element plots. Intensive parameters calculated on Fe-Ti oxides highlights the distinction between Rotorua A (Rotorua Tephra and Eastern Dome) and Trig 7693 and Middle domes. Isotopic evidence indicates the Trig 7 693 and Middle domes were supplied by a separate magma
batch to the Rotorua A phase, suggesting small ( <1 km³) magma batches were residing in close proximity.

An eruption of this size today would cause the total destruction of Rotorua City (home to >50,000 people) due to ~ 1.5 m of volcanic ejecta accumulating in this region. This would cripple the central North Island for weeks to months. Due to the length of the eruption, mitigation would be required for an extended period after the initial phase of the eruptive episode. Livestock would be severely affected from blanketing tephra, along with the complete collapse of intensive forestry operations in the Rotorua District. National and international flights from Hamilton and Auckland airports would be heavily disrupted causing major economic losses. Respiratory problems and contaminated water intake would continue for a long period after the cessation of volcanic activity.

text: The nature and dynamics of the Rotorua eruptive episode, Okataina Volcanic Centre, Taupo Volcanic Zone The 15.7 cal yrs B.P. Rotorua eruptive episode is the latest expression of western Okataina volcanism. Okataina is one of the world's most active rhyolitic volcanoes and this eruptive episode provides an ideal opportunity to examine the nature, dynamics and impacts of a large magnitude explosive eruption from this volcanic centre.

This re-investigation of the Rotorua eruptive episode has lead to the grouping of the deposits into two distinct phases of eruption. The Rotorua Tephra and Eastern Dome (previously thought to be Te Rere-related) are termed 'Rotorua A' phase. Trig 7693 andMiddle domes (previously linked to the source of the Rotorua Tephra) have been grouped with the Upper Rotorua Tephra into the. 'Rotorua B' phase. These groupings are predominantly based on mineralogy and geochemistry on samples of pyroclastic and dome deposits.

The eruptive sequence began with a small initial ash without a basalt trigger, followed soon after by a plinian fall deposit (1.62 km³) directed to the NW. Dome growth ensued (Eastern dome), creating an extensive rhyolite dome (0.72 km³) in the Okareka Embayment. Soon after Eastern dome growth (based on the absence of paleosol development) the Rotorua B phase was initiated. This phase of predominant effusive dome growth lead to the construction of the coalesced Trig 7693 and Middle domes. Periodic vulcanian explosions and dome collapses lead to the localised dispersal to the S and E, of pyroclastic density currents and fall.

A new age of 12941 ± 75 ¹⁴C years BP was obtained from charcoal in a surge deposit at a proximal site. This results in a revised age for the Rotorua eruption of 15 700 cal yrs BP. The eruption duration is estimated to exceed 15 yrs, based on a total dome volume of 1.37 km³, assuming a growth rate of 3 m ³/s.

To the NW, the Rotorua A plinian deposit (Ap-1 to Ap-10 sub units) is overall normally graded, however cm-scale bedding is evident throughout the deposit. The grain size ranges from a block-sized, basal sub unit to a medium ash, upper. The plinian tephra is biotite-poor compared to the distinct Rotorua B deposits (previously 'Upper Rotorua Tephra'), which is biotite-rich.

Whole rock geochemistry on the Rotorua A pyroclastics, forms an apparent trend, suggesting the magma supplying the explosive phase was compositional zoned prior to eruption and was subsequently disrupted immediately prior to or during eruption. The Rotorua A and B phases plot as distinct clusters in all binary element plots. Intensive parameters calculated on Fe-Ti oxides highlights the distinction between Rotorua A (Rotorua Tephra and Eastern Dome) and Trig 7693 and Middle domes. Isotopic evidence indicates the Trig 7 693 and Middle domes were supplied by a separate magma
batch to the Rotorua A phase, suggesting small ( <1 km³) magma batches were residing in close proximity.

An eruption of this size today would cause the total destruction of Rotorua City (home to >50,000 people) due to ~ 1.5 m of volcanic ejecta accumulating in this region. This would cripple the central North Island for weeks to months. Due to the length of the eruption, mitigation would be required for an extended period after the initial phase of the eruptive episode. Livestock would be severely affected from blanketing tephra, along with the complete collapse of intensive forestry operations in the Rotorua District. National and international flights from Hamilton and Auckland airports would be heavily disrupted causing major economic losses. Respiratory problems and contaminated water intake would continue for a long period after the cessation of volcanic activity.

year: 2002

title: Clustering with finite data from semi-parametric mixture distributions

authors: Wang, Yong

subjects: computer science

abstract: Existing clustering methods for the semi-parametric mixture distribution perform well as the volume of data increases. However, they all suffer from a serious drawback in finite-data situations: small outlying groups of data points can be completely ignored in the clusters that are produced, no matter how far away they lie from the major clusters. This can result in unbounded loss if the loss function is sensitive to the distance between clusters. 
This paper proposes a new distance-based clustering method that overcomes the problem by avoiding global constraints. Experimental results illustrate its superiority to existing methods when small clusters are present in finite data sets; they also suggest that it is more accurate and stable than other methods even when there are no small clusters.

text: Clustering with finite data from semi-parametric mixture distributions Existing clustering methods for the semi-parametric mixture distribution perform well as the volume of data increases. However, they all suffer from a serious drawback in finite-data situations: small outlying groups of data points can be completely ignored in the clusters that are produced, no matter how far away they lie from the major clusters. This can result in unbounded loss if the loss function is sensitive to the distance between clusters. 
This paper proposes a new distance-based clustering method that overcomes the problem by avoiding global constraints. Experimental results illustrate its superiority to existing methods when small clusters are present in finite data sets; they also suggest that it is more accurate and stable than other methods even when there are no small clusters.

year: 1999-11

title: Weaving the realities and responsibilities: Crossing culture and concepts of healing within co-existing mental health and addictive disorders.

authors: McLachlan, Andre David

subjects: Maori

abstract: Within ‘Mainstream’ western and Kaupapa Māori services, competing priorities often mean that cultural and clinical services are not implemented in unison. Without this ‘unison’, treatment of Māori with co-existing mental health and addictive disorders may be ineffective. This paper reflects the journey of a small social service agency ‘Pai Ake Solutions Limited’ (PASL) in integrating western clinical approaches within tikanga Māori values. 
Pai Ake Solutions Limited (PASL) provides a range of group and individual services to whānau who are affected by mental illness and co-existing substance use problems. The initial development of the service was based on the whakaaro of providing ‘pai ake’ (better) services for whānau in the greater Waikato. These services were initially founded on the strong values of founders Mihaka Hohua and the late Ritchie Re Cribb, which were influenced by the practices and experiences of Ngati Kahangungu, Ngati Haua, and Waikato-Maniopoto. From an initial non-clinical service provision contract, PASL began receiving referrals from individuals and whānau whose needs were not being met by mainstream service providers. Encouraging outcomes and an internal agency review of clientele utilising the service, identified that those accessing PASL services were experiencing socially and clinically significant mental and physical health, addiction and psychosocial problems.

text: Weaving the realities and responsibilities: Crossing culture and concepts of healing within co-existing mental health and addictive disorders. Within ‘Mainstream’ western and Kaupapa Māori services, competing priorities often mean that cultural and clinical services are not implemented in unison. Without this ‘unison’, treatment of Māori with co-existing mental health and addictive disorders may be ineffective. This paper reflects the journey of a small social service agency ‘Pai Ake Solutions Limited’ (PASL) in integrating western clinical approaches within tikanga Māori values. 
Pai Ake Solutions Limited (PASL) provides a range of group and individual services to whānau who are affected by mental illness and co-existing substance use problems. The initial development of the service was based on the whakaaro of providing ‘pai ake’ (better) services for whānau in the greater Waikato. These services were initially founded on the strong values of founders Mihaka Hohua and the late Ritchie Re Cribb, which were influenced by the practices and experiences of Ngati Kahangungu, Ngati Haua, and Waikato-Maniopoto. From an initial non-clinical service provision contract, PASL began receiving referrals from individuals and whānau whose needs were not being met by mainstream service providers. Encouraging outcomes and an internal agency review of clientele utilising the service, identified that those accessing PASL services were experiencing socially and clinically significant mental and physical health, addiction and psychosocial problems.

year: 2008