title: Depositional record of historic lahars in the upper Whangaehu Valley, Mt. Ruapehu, New Zealand: implications for trigger mechanisms, flow dynamics and lahar hazards

authors: Graettinger, Alison H.

subjects: lahars

abstract: Mt. Ruapehu, in the central North Island of New Zealand, is one of the most lahar-prone volcanoes in the world. Since historic observations began in 1861 AD, more than 50 individual lahars have been recorded in the Whangaehu valley alone, the natural outlet to the summit Crater Lake. These lahars have been triggered by a variety of mechanisms, including explosive eruptions that displaced Crater Lake water over the outlet or ejected it onto the snow-clad summit area of the volcano; rain-remobilisation of tephra deposits on steep slopes; displacement over the outlet as a result of syn-eruptive changes in lake bathymetry; and lake break-outs from Crater Lake following impoundment of excess water behind temporary barriers of tephra and/or ice emplaced over the outlet. However, only 9 lahar deposits can be distinguished in the upper Whangaehu valley on sedimentological, stratigraphic, geomorphic and petrological grounds, and these are skewed towards either the largest or the most recent flows. In some cases magnitude can be reconstructed from deposit geometry, with the largest lahars producing the highest level terraces, the coarsest deposits, and crossing drainage divides into normally inactive channels. This under-representation of historic events reflects the low preservation potential of unconsolidated deposits in a steep alpine environment, and the overprinting and recycling effect of large magnitude lahars that rework material down to bedrock and effectively reset the stratigraphic record. Development of magnitude-frequency relationships for Ruapehu lahars therefore requires the identification of lahar deposits in proximal, medial and distal settings in order to ensure that the full range of events is represented.

text: Depositional record of historic lahars in the upper Whangaehu Valley, Mt. Ruapehu, New Zealand: implications for trigger mechanisms, flow dynamics and lahar hazards Mt. Ruapehu, in the central North Island of New Zealand, is one of the most lahar-prone volcanoes in the world. Since historic observations began in 1861 AD, more than 50 individual lahars have been recorded in the Whangaehu valley alone, the natural outlet to the summit Crater Lake. These lahars have been triggered by a variety of mechanisms, including explosive eruptions that displaced Crater Lake water over the outlet or ejected it onto the snow-clad summit area of the volcano; rain-remobilisation of tephra deposits on steep slopes; displacement over the outlet as a result of syn-eruptive changes in lake bathymetry; and lake break-outs from Crater Lake following impoundment of excess water behind temporary barriers of tephra and/or ice emplaced over the outlet. However, only 9 lahar deposits can be distinguished in the upper Whangaehu valley on sedimentological, stratigraphic, geomorphic and petrological grounds, and these are skewed towards either the largest or the most recent flows. In some cases magnitude can be reconstructed from deposit geometry, with the largest lahars producing the highest level terraces, the coarsest deposits, and crossing drainage divides into normally inactive channels. This under-representation of historic events reflects the low preservation potential of unconsolidated deposits in a steep alpine environment, and the overprinting and recycling effect of large magnitude lahars that rework material down to bedrock and effectively reset the stratigraphic record. Development of magnitude-frequency relationships for Ruapehu lahars therefore requires the identification of lahar deposits in proximal, medial and distal settings in order to ensure that the full range of events is represented.

year: 2010

title: Comparison of simulation and experimental results of a tractor seat with nonlinear stiffness and dead-band damping

authors: Duke, Mike

abstract: A low friction tractor seat with nonlinear stiffness and dead-band damping was investigated both by simulation and experimentation. The objective was to determine if a practical, soft suspension system could be developed that offered improved vibration performance compared to a typical mechanical commercial tractor seat suspension. A hard damper was used to prevent end stop impacts that were more likely with the soft suspension. In addition the damper had a dead-band centered at the seat's static equilibrium position. The dead-band damping was achieved with a switchable damper using relative seat displacement as the control signal. The objective of the dead-band was to allow a soft undamped operating region that gave good vibration attenuation. If the relative seat displacement passed the dead-band limits due to sudden harsh inputs, the hard damping would take over and prevent end stop impacts. An experimental rig with nonlinear seat and switchable damping was built and tested with the same parameters and inputs as those used in the simulations. The simulation and experimental results compared well. Both the simulation and experimental results showed that a combination of nonlinear stiffness and dead-band damping used on a tractor seat gives reduced rms acceleration compared to a linear, conventionally damped seat.

text: Comparison of simulation and experimental results of a tractor seat with nonlinear stiffness and dead-band damping A low friction tractor seat with nonlinear stiffness and dead-band damping was investigated both by simulation and experimentation. The objective was to determine if a practical, soft suspension system could be developed that offered improved vibration performance compared to a typical mechanical commercial tractor seat suspension. A hard damper was used to prevent end stop impacts that were more likely with the soft suspension. In addition the damper had a dead-band centered at the seat's static equilibrium position. The dead-band damping was achieved with a switchable damper using relative seat displacement as the control signal. The objective of the dead-band was to allow a soft undamped operating region that gave good vibration attenuation. If the relative seat displacement passed the dead-band limits due to sudden harsh inputs, the hard damping would take over and prevent end stop impacts. An experimental rig with nonlinear seat and switchable damping was built and tested with the same parameters and inputs as those used in the simulations. The simulation and experimental results compared well. Both the simulation and experimental results showed that a combination of nonlinear stiffness and dead-band damping used on a tractor seat gives reduced rms acceleration compared to a linear, conventionally damped seat.

year: 2012

title: Evaluation of Rongo Atea: Alcohol and Other Drug Treatment Centre for Adolescents

authors: Paki, Helen Mary

subjects: Alcohol

abstract: Abstract Rongo Ātea is a residential abstinence-based Kaupapa Māori alcohol and other drug programme accommodating youth between the ages of 13 and 17. This evaluation investigates the role that staff play at Rongo Ātea along with a number of other factors including the physical environment; stages of change; programme implementation and aftercare. As a Kaupapa Māori programme, the role of how culture and identity can influence positive change is also explored along with the development of a youth-focused approach. I utilised a three phase framework borrowed from the work of Mason Durie (2008) to organise themes. These three phases, which Durie (2008) based on marae encounters, include Whakapiri (Engagement); Whakamarama (Enlightenment); and Whakamana (Empowerment) as they aptly reflect a three phase intervention approach: detoxification and early programme engagement; learning and development through ongoing programme commitment; and post treatment outcomes and aftercare. The data collection phase of this evaluation took place in 2006 and was initiated by the manager of Rongo Ātea who requested an evaluation to identify programme strengths and limitations from the perspectives of staff and students, and to make recommendations to Rongo Ātea that would assist with further programme developments. I utilised a collaborative and participatory approach (Bishop, 1996; Patton, 1990). Kaupapa Māori research principles were reflected in the use of ‘kanohi kitea’— face to face contact (Smith, 1999). With appropriate training and management support, staff could have a greater influence on programme outcomes. Evaluation findings suggest that drug and alcohol intervention and treatment for young people in New Zealand is significantly under-resourced, particularly in the areas of detoxification and aftercare. To be effective, residential treatment programmes should consist of a three stage programme covering detoxification; treatment; and aftercare incorporating an integrated approach. A greater emphasis on working with whānau alongside the young person is recommended.

text: Evaluation of Rongo Atea: Alcohol and Other Drug Treatment Centre for Adolescents Abstract Rongo Ātea is a residential abstinence-based Kaupapa Māori alcohol and other drug programme accommodating youth between the ages of 13 and 17. This evaluation investigates the role that staff play at Rongo Ātea along with a number of other factors including the physical environment; stages of change; programme implementation and aftercare. As a Kaupapa Māori programme, the role of how culture and identity can influence positive change is also explored along with the development of a youth-focused approach. I utilised a three phase framework borrowed from the work of Mason Durie (2008) to organise themes. These three phases, which Durie (2008) based on marae encounters, include Whakapiri (Engagement); Whakamarama (Enlightenment); and Whakamana (Empowerment) as they aptly reflect a three phase intervention approach: detoxification and early programme engagement; learning and development through ongoing programme commitment; and post treatment outcomes and aftercare. The data collection phase of this evaluation took place in 2006 and was initiated by the manager of Rongo Ātea who requested an evaluation to identify programme strengths and limitations from the perspectives of staff and students, and to make recommendations to Rongo Ātea that would assist with further programme developments. I utilised a collaborative and participatory approach (Bishop, 1996; Patton, 1990). Kaupapa Māori research principles were reflected in the use of ‘kanohi kitea’— face to face contact (Smith, 1999). With appropriate training and management support, staff could have a greater influence on programme outcomes. Evaluation findings suggest that drug and alcohol intervention and treatment for young people in New Zealand is significantly under-resourced, particularly in the areas of detoxification and aftercare. To be effective, residential treatment programmes should consist of a three stage programme covering detoxification; treatment; and aftercare incorporating an integrated approach. A greater emphasis on working with whānau alongside the young person is recommended.

year: 2010