title: Highly specialized microbial diversity in hyper-arid polar desert

authors: Pointing, Stephen B.

subjects: Antarctica

abstract: The McMurdo Dry Valleys in Antarctica are a cold hyperarid polar desert that present extreme challenges to life. Here, we report a culture-independent survey of multidomain microbial biodiversity in McKelvey Valley, a pristine example of the coldest desert on Earth. We demonstrate that life has adapted to form highly-specialized communities in distinct lithic niches occurring concomitantly within this terrain. Endoliths and chasmoliths in sandstone displayed greatest diversity, whereas soil was relatively depauperate and lacked a significant photoautotrophic component, apart from isolated islands of hypolithic cyanobacterial colonization on quartz rocks in soil contact. Communities supported previously unreported polar bacteria and fungi, but archaea were absent from all niches. Lithic community structure did not vary significantly on a landscape scale and stochastic moisture input due to snowmelt resulted in increases in colonization frequency without significantly affecting diversity. The findings show that biodiversity near the cold-arid limit for life is more complex than previously appreciated, but communities lack variability probably due to the high selective pressures of this extreme environment.

text: Highly specialized microbial diversity in hyper-arid polar desert The McMurdo Dry Valleys in Antarctica are a cold hyperarid polar desert that present extreme challenges to life. Here, we report a culture-independent survey of multidomain microbial biodiversity in McKelvey Valley, a pristine example of the coldest desert on Earth. We demonstrate that life has adapted to form highly-specialized communities in distinct lithic niches occurring concomitantly within this terrain. Endoliths and chasmoliths in sandstone displayed greatest diversity, whereas soil was relatively depauperate and lacked a significant photoautotrophic component, apart from isolated islands of hypolithic cyanobacterial colonization on quartz rocks in soil contact. Communities supported previously unreported polar bacteria and fungi, but archaea were absent from all niches. Lithic community structure did not vary significantly on a landscape scale and stochastic moisture input due to snowmelt resulted in increases in colonization frequency without significantly affecting diversity. The findings show that biodiversity near the cold-arid limit for life is more complex than previously appreciated, but communities lack variability probably due to the high selective pressures of this extreme environment.

year: 2009-11-24

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: Aihe Pepene

authors: Hart, Philip

abstract: Sharing the same illustrious whakapapa as his brother Reha Aperahama, Aihe Pepene was prominent when living in the Thames district before settling at Te Aroha in 1878. When speculators tried to acquire the Thames foreshore from Pepene and others in 1870, he became involved in the subsequent legal actions over unpaid promissory notes. Later he would acquire interests in many blocks of land, and received a steady income by leasing or selling these plus his share in the goldfields revenue. When the Aroha Block was considered by the land court for the last time, in 1878, he conducted the case for Ngati Rahiri.
He invested in four Hauraki goldfields, and was briefly an owner and skipper of two small river steamers, an unsuccessful endeavour that resulted in his being forced to sell more land to meet his debts. Once his 1880 and 1881 financial difficulties were resolved, no more such problems recurred. 
A leading rangatira in Hauraki generally as well as at Te Aroha, he would be elected to a Maori Committee that was soon revealed to have no significance. Closely involved with Pakeha, he assisted settlement, and his loyalty to the Crown was illustrated by his becoming an officer in the Thames Native Volunteer Corps. A member of the Church of England for many years, like many Maori he became a Mormon, a faith perhaps more appropriate to his private life, for he had more than one wife, notoriously eloping with the wife of a more senior rangatira despite already being married.

text: Aihe Pepene Sharing the same illustrious whakapapa as his brother Reha Aperahama, Aihe Pepene was prominent when living in the Thames district before settling at Te Aroha in 1878. When speculators tried to acquire the Thames foreshore from Pepene and others in 1870, he became involved in the subsequent legal actions over unpaid promissory notes. Later he would acquire interests in many blocks of land, and received a steady income by leasing or selling these plus his share in the goldfields revenue. When the Aroha Block was considered by the land court for the last time, in 1878, he conducted the case for Ngati Rahiri.
He invested in four Hauraki goldfields, and was briefly an owner and skipper of two small river steamers, an unsuccessful endeavour that resulted in his being forced to sell more land to meet his debts. Once his 1880 and 1881 financial difficulties were resolved, no more such problems recurred. 
A leading rangatira in Hauraki generally as well as at Te Aroha, he would be elected to a Maori Committee that was soon revealed to have no significance. Closely involved with Pakeha, he assisted settlement, and his loyalty to the Crown was illustrated by his becoming an officer in the Thames Native Volunteer Corps. A member of the Church of England for many years, like many Maori he became a Mormon, a faith perhaps more appropriate to his private life, for he had more than one wife, notoriously eloping with the wife of a more senior rangatira despite already being married.

year: 2016