title: Modelling volcanic tsunamis

authors: Prasetya, Gegar Sapta

subjects: tsunamis

abstract: Tsunamis generated by volcanic eruptions have caused about 25% of all deaths associated with volcano activity. The 1883 Krakatau eruption is one example of a fairly recent eruption that produced large tsunamis (-35 m) which caused a high death toll. Concern has also been raised by the potential tsunami generation of the Auckland Volcanic Field, and the impact of such events on the Auckland Region.
Although the generation of tsunamis by volcanic eruptions is a major hazard, the processes of tsunami generation are poorly understood. A review of volcanic tsunamis identified 10 main mechanisms. Four of these - caldera collapse, debris avalanches, submarine explosions, and pyroclastic flows - have been suggested as the mechanisms producing the largest tsunamis. All four mechanisms have also been suggested as being responsible for the tsunamis produced by the Krakatau eruption.
A combination of physical and numerical modelling was used to develop predictive tools to be applied to volcanoes in Indonesia and New Zealand. The physical modelling involved two main investigations:
• A 3 dimensional scale model of the Straits of Sunda and Krakatau. This examined the nature of tsunamis produced by caldera collapse, submarine explosions, and water displacement by debris avalanches and pyroclastic flows.
• A series of 2 dimensional simulations of the entrance of pyroclastic flows into the sea. A finite element numerical model was applied to the simulation of pyroclastic flow, maar formation and submarine explosion generation of tsunamis within the Auckland Volcanic Field.
The physical and numerical model results indicate that large scale pyroclastic flows are probably the cause of the main 1883 Krakatau tsunamis. A tsunami wave can easily be generated by gravity flows entering the water, regardless of the slope. The wave properties depend on the relative densities of the flow and the receiving body, and the velocity of the flow. The angle of entry of the flow into the water determines the deposition pattern of sediment. The formation of the Calmeyers and Steers shallow area on Krakatau event 1883 was reproduced by the pyroclastic experiments using coarse sand and mud with steep entry angle ~ 60°). The more dilute upper component of the pyroclastic flow that traveled along the sea surface for up to 45 km and killed more than 1000 people at Katimbang, Sumatera Island can also be explained. The experiments showed that less dense material from the pyroclastic flow propagates near the water surface. This is even more likely if the material is hot and gas-rich.
Physical and numerical model results showed that a single explosion cannot produce a high wave. If a super violent explosion did occur during the Krakatau event, then the water waves (tsunamis) that caused the devastating effect on the surrounding island coastal land were not caused by the direct transfer of explosive forces. Instead a sequence of one or more pyroclastic flows, or collapsing column in and around the Krakatau complex are the most likely mechanism causing the largest tsunami.
Numerical modelling of the Auckland Volcanic Field examined 4 scenarios:
• A series of submarine explosion;
• Pyroclastic flows from Rangitoto Island;
• Pyroclastic flows from Browns (Motukorea) Island;
• Submarine explosion within the Tamaki Estuary.
The first 3 scenarios produced regional effects, while the last was purely local event.
It was also found that the efficiency of the submarine explosion mechanism was increased by using a sequence of smaller explosions, instead of one large explosion. However the timing between explosions was found to be critical; if the explosions are too close together or too far apart, the efficiency decreases. It is considered that the optimal timing will vary with water depth and explosive yield.
The numerical modelling showed that volcanic tsunamis are not a major threat to Auckland. However under suitable conditions a volcanic eruption could produce moderately large tsunamis that generate strong currents.

text: Modelling volcanic tsunamis Tsunamis generated by volcanic eruptions have caused about 25% of all deaths associated with volcano activity. The 1883 Krakatau eruption is one example of a fairly recent eruption that produced large tsunamis (-35 m) which caused a high death toll. Concern has also been raised by the potential tsunami generation of the Auckland Volcanic Field, and the impact of such events on the Auckland Region.
Although the generation of tsunamis by volcanic eruptions is a major hazard, the processes of tsunami generation are poorly understood. A review of volcanic tsunamis identified 10 main mechanisms. Four of these - caldera collapse, debris avalanches, submarine explosions, and pyroclastic flows - have been suggested as the mechanisms producing the largest tsunamis. All four mechanisms have also been suggested as being responsible for the tsunamis produced by the Krakatau eruption.
A combination of physical and numerical modelling was used to develop predictive tools to be applied to volcanoes in Indonesia and New Zealand. The physical modelling involved two main investigations:
• A 3 dimensional scale model of the Straits of Sunda and Krakatau. This examined the nature of tsunamis produced by caldera collapse, submarine explosions, and water displacement by debris avalanches and pyroclastic flows.
• A series of 2 dimensional simulations of the entrance of pyroclastic flows into the sea. A finite element numerical model was applied to the simulation of pyroclastic flow, maar formation and submarine explosion generation of tsunamis within the Auckland Volcanic Field.
The physical and numerical model results indicate that large scale pyroclastic flows are probably the cause of the main 1883 Krakatau tsunamis. A tsunami wave can easily be generated by gravity flows entering the water, regardless of the slope. The wave properties depend on the relative densities of the flow and the receiving body, and the velocity of the flow. The angle of entry of the flow into the water determines the deposition pattern of sediment. The formation of the Calmeyers and Steers shallow area on Krakatau event 1883 was reproduced by the pyroclastic experiments using coarse sand and mud with steep entry angle ~ 60°). The more dilute upper component of the pyroclastic flow that traveled along the sea surface for up to 45 km and killed more than 1000 people at Katimbang, Sumatera Island can also be explained. The experiments showed that less dense material from the pyroclastic flow propagates near the water surface. This is even more likely if the material is hot and gas-rich.
Physical and numerical model results showed that a single explosion cannot produce a high wave. If a super violent explosion did occur during the Krakatau event, then the water waves (tsunamis) that caused the devastating effect on the surrounding island coastal land were not caused by the direct transfer of explosive forces. Instead a sequence of one or more pyroclastic flows, or collapsing column in and around the Krakatau complex are the most likely mechanism causing the largest tsunami.
Numerical modelling of the Auckland Volcanic Field examined 4 scenarios:
• A series of submarine explosion;
• Pyroclastic flows from Rangitoto Island;
• Pyroclastic flows from Browns (Motukorea) Island;
• Submarine explosion within the Tamaki Estuary.
The first 3 scenarios produced regional effects, while the last was purely local event.
It was also found that the efficiency of the submarine explosion mechanism was increased by using a sequence of smaller explosions, instead of one large explosion. However the timing between explosions was found to be critical; if the explosions are too close together or too far apart, the efficiency decreases. It is considered that the optimal timing will vary with water depth and explosive yield.
The numerical modelling showed that volcanic tsunamis are not a major threat to Auckland. However under suitable conditions a volcanic eruption could produce moderately large tsunamis that generate strong currents.

year: 1998

title: Methods of a national colorectal cancer cohort study: the PIPER Project

authors: Firth, Melissa

abstract: A national study looking at bowel cancer in New Zealand has previously been completed (the PIPER Project). The study included 5,610 patients and collected medical information about how each person was found to have bowel cancer and the treatment they received. This paper reports how the study was carried out. The information collected in the study will be used to look at the quality of care being provided to New Zealand patients with bowel cancer, and to find out if differences in care occur based on where people live, their ethnicity and their socioeconomic status.

text: Methods of a national colorectal cancer cohort study: the PIPER Project A national study looking at bowel cancer in New Zealand has previously been completed (the PIPER Project). The study included 5,610 patients and collected medical information about how each person was found to have bowel cancer and the treatment they received. This paper reports how the study was carried out. The information collected in the study will be used to look at the quality of care being provided to New Zealand patients with bowel cancer, and to find out if differences in care occur based on where people live, their ethnicity and their socioeconomic status.

year: 2016

title: The COVID-19 domestic vaccine pass: Implications for Māori

authors: Kukutai, Tahu

abstract: The New Zealand government has introduced a COVID-19 domestic vaccine pass to be used in conjunction with the COVID-19 Protection Framework. The Framework is likely to be activated soon after Cabinet meets on 29 November 2021. The pass will be necessary to access places and events that require proof of vaccination under the Framework.
This brief does not argue for or against the introduction of a domestic vaccine pass, but rather discusses key issues that it raises for Māori, and suggests actions to address them. We see four key issues:
• the lack of Māori involvement, as a Tiriti partner, on either the design or implementation of the COVID-19 domestic vaccine pass;
• disproportionate restriction on Māori mobility due to lower Māori vaccination rates;
• privacy and data security concerns;
• uneven implementation that could increase discrimination against Māori and other groups considered to pose a risk to others’ safety.
To respond to these issues we recommend that the implementation of the pass be designed in partnership with Māori and comply with Māori data sovereignty requirements. As Tiriti partners, Māori should expect that the pass will keep their communities safe, while providing opportunities to enact manaakitanga in the matrix of care, and the mana to manage their own affairs.

text: The COVID-19 domestic vaccine pass: Implications for Māori The New Zealand government has introduced a COVID-19 domestic vaccine pass to be used in conjunction with the COVID-19 Protection Framework. The Framework is likely to be activated soon after Cabinet meets on 29 November 2021. The pass will be necessary to access places and events that require proof of vaccination under the Framework.
This brief does not argue for or against the introduction of a domestic vaccine pass, but rather discusses key issues that it raises for Māori, and suggests actions to address them. We see four key issues:
• the lack of Māori involvement, as a Tiriti partner, on either the design or implementation of the COVID-19 domestic vaccine pass;
• disproportionate restriction on Māori mobility due to lower Māori vaccination rates;
• privacy and data security concerns;
• uneven implementation that could increase discrimination against Māori and other groups considered to pose a risk to others’ safety.
To respond to these issues we recommend that the implementation of the pass be designed in partnership with Māori and comply with Māori data sovereignty requirements. As Tiriti partners, Māori should expect that the pass will keep their communities safe, while providing opportunities to enact manaakitanga in the matrix of care, and the mana to manage their own affairs.

year: 2021-11-30