title: Depositional record of historic lahars in the Whangaehu Gorge, Mt. Ruapehu

authors: Graettinger, Alison Hollomon

subjects: lahars

abstract: Mt. Ruapehu is one of the most lahar prone volcanoes in the world, having both a crater lake and six small glaciers upon its 2797 m summit.  The major outlet for the crater lake, the Whangaehu Gorge, has hosted over 46 historic lahars.  However, the low preservation of debris flow deposits, as a result of frequent remobilisation on steep slopes, allows for the detailed description of only 9 lahar events over the last 150 years.  Field investigation, historic aerial photos, two airborne LiDAR surveys and direct measurements have been utilised to describe the sedimentology, geomorphology and distribution of historic lahar deposits in the first 11 km of the Whangaehu Gorge.  Inundation maps have been created for 1945, 1953, 1975, September 1995, October 1995, March 2007 and September 2007.  Grain size distribution, componentry and geomorphology of the 1861, 1975, September 1995, October 1995, 1999 and 2007 lahar deposits have been compared.

The lahar deposits are massive, very poorly sorted, silty gravels that form a series of unconsolidated terraces.  The limited sediment sources in the steep sided Whangaehu Gorge, including minor historic eruption products, results in significant recycling of lahar deposits.  However, the deposits can be differentiated by proportions of lithological components and in some cases anthropogenic debris.  The abundance of hydrothermally altered material reflects the role of Crater Lake in lahar formation, although, some of these materials (gypsum, sulphur and snow) are only temporary. 

Non-cohesive debris flows and occasional snow slurry lahars have been formed by a range of triggering mechanisms associated with and independent of eruptions.  Lahars have been formed in the Whangaehu Valley as the result of ejected crater lake water and associated snow melt (1975, September 1995 and September 2007), as well as the progressive displacement of lake water as a result of lava dome growth (1945) and uplift of the lake floor (1968).  Inter-eruption lahars occur as a result of Crater Lake outburst floods (1861, 1953 and March 2007) and remobilisation by precipitation and the collapse of tephra laden snow (October 1995 and 1999).  

The comparison of historic lahars also reflects the range of lahar magnitudes experienced historically on Ruapehu.  The most recent Crater Lake outburst of March 2007, with a peak discharge of 1700-2500 m3/s is the second largest recorded lahar, behind only the eruption-generated lahar of April 1975 with a peak discharge of 5000-7500 m3/s.

Lahar mitigation can subsequently be based on lahar generation and incorporation of the vast amounts of data collected before and after the 2007 outburst flood.  Recent remobilisation and phreatic activity suggest the significant under-representation of small volume events like rain-generated and snow slurry lahars in the geologic record.

text: Depositional record of historic lahars in the Whangaehu Gorge, Mt. Ruapehu Mt. Ruapehu is one of the most lahar prone volcanoes in the world, having both a crater lake and six small glaciers upon its 2797 m summit.  The major outlet for the crater lake, the Whangaehu Gorge, has hosted over 46 historic lahars.  However, the low preservation of debris flow deposits, as a result of frequent remobilisation on steep slopes, allows for the detailed description of only 9 lahar events over the last 150 years.  Field investigation, historic aerial photos, two airborne LiDAR surveys and direct measurements have been utilised to describe the sedimentology, geomorphology and distribution of historic lahar deposits in the first 11 km of the Whangaehu Gorge.  Inundation maps have been created for 1945, 1953, 1975, September 1995, October 1995, March 2007 and September 2007.  Grain size distribution, componentry and geomorphology of the 1861, 1975, September 1995, October 1995, 1999 and 2007 lahar deposits have been compared.

The lahar deposits are massive, very poorly sorted, silty gravels that form a series of unconsolidated terraces.  The limited sediment sources in the steep sided Whangaehu Gorge, including minor historic eruption products, results in significant recycling of lahar deposits.  However, the deposits can be differentiated by proportions of lithological components and in some cases anthropogenic debris.  The abundance of hydrothermally altered material reflects the role of Crater Lake in lahar formation, although, some of these materials (gypsum, sulphur and snow) are only temporary. 

Non-cohesive debris flows and occasional snow slurry lahars have been formed by a range of triggering mechanisms associated with and independent of eruptions.  Lahars have been formed in the Whangaehu Valley as the result of ejected crater lake water and associated snow melt (1975, September 1995 and September 2007), as well as the progressive displacement of lake water as a result of lava dome growth (1945) and uplift of the lake floor (1968).  Inter-eruption lahars occur as a result of Crater Lake outburst floods (1861, 1953 and March 2007) and remobilisation by precipitation and the collapse of tephra laden snow (October 1995 and 1999).  

The comparison of historic lahars also reflects the range of lahar magnitudes experienced historically on Ruapehu.  The most recent Crater Lake outburst of March 2007, with a peak discharge of 1700-2500 m3/s is the second largest recorded lahar, behind only the eruption-generated lahar of April 1975 with a peak discharge of 5000-7500 m3/s.

Lahar mitigation can subsequently be based on lahar generation and incorporation of the vast amounts of data collected before and after the 2007 outburst flood.  Recent remobilisation and phreatic activity suggest the significant under-representation of small volume events like rain-generated and snow slurry lahars in the geologic record.

year: 2008

title: Boosting decision stumps for dynamic feature selection on data streams

authors: Barddal, Jean Paul

subjects: computer science

abstract: Feature selection targets the identification of which features of a dataset are relevant to the learning task. It is also widely known and used to improve computation times, reduce computation requirements, and to decrease the impact of the curse of dimensionality and enhancing the generalization rates of classifiers. In data streams, classifiers shall benefit from all the items above, but more importantly, from the fact that the relevant subset of features may drift over time. In this paper, we propose a novel dynamic feature selection method for data streams called Adaptive Boosting for Feature Selection (ABFS). ABFS chains decision stumps and drift detectors, and as a result, identifies which features are relevant to the learning task as the stream progresses with reasonable success. In addition to our proposed algorithm, we bring feature selection-specific metrics from batch learning to streaming scenarios. Next, we evaluate ABFS according to these metrics in both synthetic and real-world scenarios. As a result, ABFS improves the classification rates of different types of learners and eventually enhances computational resources usage.

text: Boosting decision stumps for dynamic feature selection on data streams Feature selection targets the identification of which features of a dataset are relevant to the learning task. It is also widely known and used to improve computation times, reduce computation requirements, and to decrease the impact of the curse of dimensionality and enhancing the generalization rates of classifiers. In data streams, classifiers shall benefit from all the items above, but more importantly, from the fact that the relevant subset of features may drift over time. In this paper, we propose a novel dynamic feature selection method for data streams called Adaptive Boosting for Feature Selection (ABFS). ABFS chains decision stumps and drift detectors, and as a result, identifies which features are relevant to the learning task as the stream progresses with reasonable success. In addition to our proposed algorithm, we bring feature selection-specific metrics from batch learning to streaming scenarios. Next, we evaluate ABFS according to these metrics in both synthetic and real-world scenarios. As a result, ABFS improves the classification rates of different types of learners and eventually enhances computational resources usage.

year: 2019

title: Consequences of cultural satisfaction at work: A study of New Zealand Māori

authors: Haar, Jarrod M.

subjects: cultural satisfaction at work

abstract: To expand our understanding of indigenous workers and the importance of indigenous culture in the workplace, we tested the outcomes of cultural satisfaction at work using structural equation modelling with a sample of 174 Māori employees. We show that, consistent with social exchange theory, Māori who are more satisfied with the level of understanding of their cultural values in the workplace report better job outcomes. Cultural satisfaction at work directly predicted loyalty and organisational citizenship behaviours (OCBs). Furthermore, direct-effects and mediation models were tested, showing that loyalty fully mediated the influence of cultural satisfaction at work on OCBs. The implications for HRM are that indigenous workers who are more satisfied with the way their cultural beliefs are valued in the workplace are likely to be more loyal and may be superior performance. The findings highlight the importance for employers of having regard to the culture of their indigenous workers.

text: Consequences of cultural satisfaction at work: A study of New Zealand Māori To expand our understanding of indigenous workers and the importance of indigenous culture in the workplace, we tested the outcomes of cultural satisfaction at work using structural equation modelling with a sample of 174 Māori employees. We show that, consistent with social exchange theory, Māori who are more satisfied with the level of understanding of their cultural values in the workplace report better job outcomes. Cultural satisfaction at work directly predicted loyalty and organisational citizenship behaviours (OCBs). Furthermore, direct-effects and mediation models were tested, showing that loyalty fully mediated the influence of cultural satisfaction at work on OCBs. The implications for HRM are that indigenous workers who are more satisfied with the way their cultural beliefs are valued in the workplace are likely to be more loyal and may be superior performance. The findings highlight the importance for employers of having regard to the culture of their indigenous workers.

year: 2011