title: Towards a Better Understanding of Coastal Cliff Erosion in Waitemata Group Rock; Auckland, New Zealand.

authors: Bell, Jessica Emily

subjects: Waitemata Group

abstract: The soft sedimentary deposits of the Waitemata Group which outcrop on the eastern coastline of the Auckland region are a coastal cliff erosion hazard. The determination of the rate that these cliffs erode for hazard zonation purposes still requires research. A database has been collated of a range of structural, geological, geomorphic and climate parameters from 16 representative cliff sites in order to statistically assess what parameters influence cliff erosion and why erosion rates vary within the relatively uniform geology. 

Four different lithological units have been defined: sandstone beds of turbidites; sandstone beds of densites (contain rip-up clasts); sand to gravel beds of debrites; and siltstone beds. Cliff rock has very weak to weak intact rock strength; apertures of 0.1 to 15 mm; infill types are soft clay and grit, and hard calcite and iron; spacing of discontinuities are smaller in siltstone beds (≥ 5 mm), and up to 5 m in sandstone and debrite beds; bedding and fault planes are continuous, joints are non-continuous; block size is dictated by bed thickness and non-continuous joints. Shore platform widths were used to determine long-term erosion rates which range from 1.2 to 53.0 mm y-1. Platform morphologies are either sloping or horizontal or are a combination of both. Higher platform benches found at some sites are considered to be the result of a higher period of sea-level or are high-tide benches. Intact and rock mass strength increases northwards. Cliff heights are 8 to 38 m; cliff angles are 51 to 79 . Conditions for sporadic planar and wedge failure were determined at some sites; frittered siltstone and low durability sandstone allow smaller-scale, continual erosion. Castor Bay, Army Bay, Waiwera Beach and Leigh Marine Reserve have the lowest rock mass quality. Musick Point, Narrowneck Beach and Waiake Bay have good rock mass quality.

A conceptual model for coastal cliff erosion has been developed for Waitemata Group coastal cliffs, based on the dominant processes that act on the cliffs determined from statistical analysis (student t-test, correlation and regression) and field observations. The primary factor for cliff erosion is bed dip, whereby seaward dipping beds have higher erosion rates than landward dipping beds. The secondary factors for cliff erosion include: the intact and rock mass strength of the rock; the rock mass quality; strength of the siltstone beds; strength and structure of the sandstone beds; and orientation of the bedding planes with respect to the cliff face. Shear stresses are enhanced when beds dip seaward and thus shear failure along continuous surfaces is achievable. When beds dip landward the influence of shear stresses along bedding planes, and their contribution to the removal of individual blocks of rock, is severely inhibited resulting in reduced rates of erosion.  There is no relationship between cliff height and erosion rates and cliff heights are mainly controlled by the pre-existing landscape. Cliff angle is controlled by the proportion of sandstone and siltstone (whereby lower cliff angles are more siltstone-dominated), rock mass strength and weathering.  Erosion rates do vary in Waitemata Group rock of the Auckland region because of the variation in structural and geomorphic conditions of the cliff, most strongly controlled by the dip angle of bedding planes.

text: Towards a Better Understanding of Coastal Cliff Erosion in Waitemata Group Rock; Auckland, New Zealand. The soft sedimentary deposits of the Waitemata Group which outcrop on the eastern coastline of the Auckland region are a coastal cliff erosion hazard. The determination of the rate that these cliffs erode for hazard zonation purposes still requires research. A database has been collated of a range of structural, geological, geomorphic and climate parameters from 16 representative cliff sites in order to statistically assess what parameters influence cliff erosion and why erosion rates vary within the relatively uniform geology. 

Four different lithological units have been defined: sandstone beds of turbidites; sandstone beds of densites (contain rip-up clasts); sand to gravel beds of debrites; and siltstone beds. Cliff rock has very weak to weak intact rock strength; apertures of 0.1 to 15 mm; infill types are soft clay and grit, and hard calcite and iron; spacing of discontinuities are smaller in siltstone beds (≥ 5 mm), and up to 5 m in sandstone and debrite beds; bedding and fault planes are continuous, joints are non-continuous; block size is dictated by bed thickness and non-continuous joints. Shore platform widths were used to determine long-term erosion rates which range from 1.2 to 53.0 mm y-1. Platform morphologies are either sloping or horizontal or are a combination of both. Higher platform benches found at some sites are considered to be the result of a higher period of sea-level or are high-tide benches. Intact and rock mass strength increases northwards. Cliff heights are 8 to 38 m; cliff angles are 51 to 79 . Conditions for sporadic planar and wedge failure were determined at some sites; frittered siltstone and low durability sandstone allow smaller-scale, continual erosion. Castor Bay, Army Bay, Waiwera Beach and Leigh Marine Reserve have the lowest rock mass quality. Musick Point, Narrowneck Beach and Waiake Bay have good rock mass quality.

A conceptual model for coastal cliff erosion has been developed for Waitemata Group coastal cliffs, based on the dominant processes that act on the cliffs determined from statistical analysis (student t-test, correlation and regression) and field observations. The primary factor for cliff erosion is bed dip, whereby seaward dipping beds have higher erosion rates than landward dipping beds. The secondary factors for cliff erosion include: the intact and rock mass strength of the rock; the rock mass quality; strength of the siltstone beds; strength and structure of the sandstone beds; and orientation of the bedding planes with respect to the cliff face. Shear stresses are enhanced when beds dip seaward and thus shear failure along continuous surfaces is achievable. When beds dip landward the influence of shear stresses along bedding planes, and their contribution to the removal of individual blocks of rock, is severely inhibited resulting in reduced rates of erosion.  There is no relationship between cliff height and erosion rates and cliff heights are mainly controlled by the pre-existing landscape. Cliff angle is controlled by the proportion of sandstone and siltstone (whereby lower cliff angles are more siltstone-dominated), rock mass strength and weathering.  Erosion rates do vary in Waitemata Group rock of the Auckland region because of the variation in structural and geomorphic conditions of the cliff, most strongly controlled by the dip angle of bedding planes.

year: 2007

title: Limited role of climate change in extreme low rainfall associated with southern Madagascar food insecurity, 2019–21

authors: Harrington, Luke J.

abstract: Southern Madagascar recently experienced a severe food security crisis, made significantly worse by well below average rainfall from July 2019 to June 2021. This exceptional drought has affected a region with high pre-existing levels of vulnerability to food insecurity (subsistence agriculture and pastoralism in the region is rain-fed only), while impacts have been compounded further by COVID-19 restrictions and pest infestations. The rainy seasons of both 2019/20 and 2020/21 saw just 60% of normal rainfall across the Grand South region and was estimated as a 1-in-135 year dry event, only surpassed in severity by the devastating drought of 1990–92. Based on a combination of observations and climate modelling, the likelihood of experiencing such poor rains in the region was not significantly increased due to human-caused climate change: while the observations and models combine to indicate a small shift toward more droughts like the 2019–2021 event as a consequence of climate change, these trends remain overwhelmed by natural variability. This result is consistent with previous research, with the Intergovernmental Panel on Climate Change (IPCC)'s Sixth Assessment Report concluding that any perceptible changes in drought will only emerge in this region if global mean temperatures exceed 2 °C above pre-industrial levels.

text: Limited role of climate change in extreme low rainfall associated with southern Madagascar food insecurity, 2019–21 Southern Madagascar recently experienced a severe food security crisis, made significantly worse by well below average rainfall from July 2019 to June 2021. This exceptional drought has affected a region with high pre-existing levels of vulnerability to food insecurity (subsistence agriculture and pastoralism in the region is rain-fed only), while impacts have been compounded further by COVID-19 restrictions and pest infestations. The rainy seasons of both 2019/20 and 2020/21 saw just 60% of normal rainfall across the Grand South region and was estimated as a 1-in-135 year dry event, only surpassed in severity by the devastating drought of 1990–92. Based on a combination of observations and climate modelling, the likelihood of experiencing such poor rains in the region was not significantly increased due to human-caused climate change: while the observations and models combine to indicate a small shift toward more droughts like the 2019–2021 event as a consequence of climate change, these trends remain overwhelmed by natural variability. This result is consistent with previous research, with the Intergovernmental Panel on Climate Change (IPCC)'s Sixth Assessment Report concluding that any perceptible changes in drought will only emerge in this region if global mean temperatures exceed 2 °C above pre-industrial levels.

year: 2022-12-01

title: Respecting and recognising Indigenous rights when challenged by commercial activities

authors: Toki, Valmaine

abstract: The United Nations Declaration on the Rights of Indigenous Peoples was hailed as a triumph among Indigenous peoples, signalling a long-awaited recognition of their fundamental human rights. Despite this, many violations of these basic rights continue, particularly in relation to extractive industries and business activities. In response, a business reference guide seeks to inform industries of their responsibilities. This article examines the tenuous relationship between Indigenous rights, state responsibilities and business expectations.

text: Respecting and recognising Indigenous rights when challenged by commercial activities The United Nations Declaration on the Rights of Indigenous Peoples was hailed as a triumph among Indigenous peoples, signalling a long-awaited recognition of their fundamental human rights. Despite this, many violations of these basic rights continue, particularly in relation to extractive industries and business activities. In response, a business reference guide seeks to inform industries of their responsibilities. This article examines the tenuous relationship between Indigenous rights, state responsibilities and business expectations.

year: 2018