title: Using soil stratigraphy and tephrochronology to understand the origin, age, and classification of a unique Late Quaternary tephra-derived Ultisol in Aotearoa New Zealand

authors: Lowe, David J.

subjects: pedology

abstract: In this article, I show how an Ultisol, representative of a globally-important group of soils with clay-rich subsoils, low base saturation, and low fertility, in the central Waikato region in northern North Island, can be evaluated using soil stratigraphy and tephrochronology to answer challenging questions about its genesis, age and classification. The Kainui soil, a Typic Kandiudult (Soil Taxonomy) and Buried-granular Yellow Ultic Soil (New Zealand Soil Classification), occurs on low rolling hills of Mid-Quaternary age mainly in the Hamilton lowlands in, and north and northeast of, Hamilton city. It is a composite, multi-layered tephra-derived soil consisting of two distinct parts, upper and lower. The upper part is a coverbed typically c. 0.4–0.7 m in thickness (c. 0.6 m on average) comprising numerous late Quaternary rhyolitic and andesitic tephras that have been accumulating incrementally since c. 50 ka (the age of Rotoehu Ash at the coverbed’s base) whilst simultaneously being pedogenically altered (i.e., forming soil horizons) via developmental upbuilding pedogenesis during Marine Oxygen Isotope Stages (MOIS) 3-1. Any original depositional (fall) bedding has been almost entirely masked by pedogenic alteration. Sediments in lakes aged c. 20 ka adjacent to the low hills have preserved around 40 separate, thin, macroscopic tephra-fall beds mainly rhyolitic in composition, and equivalent subaerial deposits together form the upper c. 30 cm of the coverbed. Okareka (c. 21.8 ka), Okaia (c. 28.6 ka), Tahuna (c. 39.3 ka) and (especially) Rotoehu tephras make up the bulk of the lower c. 30 cm of the coverbed. Tephra admixing has occurred throughout the coverbed because of soil upbuilding processes. Moderately well drained, this upper profile is dominated by halloysite (not allophane) in the clay fraction because of limited desilication. In contrast, Otorohanga soils, on rolling hills to the south of Hamilton, are formed in equivalent but thicker (>c. 0.8 m) late Quaternary tephras ≤c. 50 ka that are somewhat more andesitic although predominantly rhyolitic overall. These deeper soils are well drained with strong desilication and thus are allophanic, generating Typic Hapludands. Ubiquitous redox features, together with short-lived contemporary reduction observed in the lower coverbed of a Kainui soil profile, indicate that the Kainui soil in general is likely to be saturated by perching for several days, or near saturation for several months, each year. The perching occurs because the coverbed overlies a slowly-permeable, buried, clay-rich paleosol on upper Hamilton Ash beds, >c. 50 ka in age, which makes up the lower part of the two-storeyed Kainui soil. The coverbed-paleosol boundary is a lithologic discontinuity (unconformity). Irregular in shape, it represents a tree-overturn paleosurface that may be c. 74 ka in age (MOIS 5/4 boundary). The buried paleosol is markedly altered and halloysitic with relict clay skins (forming paleo-argillic and/or paleo-kandic horizons) and redoximorphic features. It is inferred to have formed via developmental upbuilding pedogenesis during the Last Interglacial (MOIS 5e). The entire Hamilton Ash sequence, c. 3 m in thickness and overlain unconformably by Rotoehu Ash and underlain by c. 340-ka Rangitawa Tephra at the base, represents a thick composite (accretionary) set of clayey, welded paleosols developed by upbuilding pedogenesis from MOIS 10 to 5.

text: Using soil stratigraphy and tephrochronology to understand the origin, age, and classification of a unique Late Quaternary tephra-derived Ultisol in Aotearoa New Zealand In this article, I show how an Ultisol, representative of a globally-important group of soils with clay-rich subsoils, low base saturation, and low fertility, in the central Waikato region in northern North Island, can be evaluated using soil stratigraphy and tephrochronology to answer challenging questions about its genesis, age and classification. The Kainui soil, a Typic Kandiudult (Soil Taxonomy) and Buried-granular Yellow Ultic Soil (New Zealand Soil Classification), occurs on low rolling hills of Mid-Quaternary age mainly in the Hamilton lowlands in, and north and northeast of, Hamilton city. It is a composite, multi-layered tephra-derived soil consisting of two distinct parts, upper and lower. The upper part is a coverbed typically c. 0.4–0.7 m in thickness (c. 0.6 m on average) comprising numerous late Quaternary rhyolitic and andesitic tephras that have been accumulating incrementally since c. 50 ka (the age of Rotoehu Ash at the coverbed’s base) whilst simultaneously being pedogenically altered (i.e., forming soil horizons) via developmental upbuilding pedogenesis during Marine Oxygen Isotope Stages (MOIS) 3-1. Any original depositional (fall) bedding has been almost entirely masked by pedogenic alteration. Sediments in lakes aged c. 20 ka adjacent to the low hills have preserved around 40 separate, thin, macroscopic tephra-fall beds mainly rhyolitic in composition, and equivalent subaerial deposits together form the upper c. 30 cm of the coverbed. Okareka (c. 21.8 ka), Okaia (c. 28.6 ka), Tahuna (c. 39.3 ka) and (especially) Rotoehu tephras make up the bulk of the lower c. 30 cm of the coverbed. Tephra admixing has occurred throughout the coverbed because of soil upbuilding processes. Moderately well drained, this upper profile is dominated by halloysite (not allophane) in the clay fraction because of limited desilication. In contrast, Otorohanga soils, on rolling hills to the south of Hamilton, are formed in equivalent but thicker (>c. 0.8 m) late Quaternary tephras ≤c. 50 ka that are somewhat more andesitic although predominantly rhyolitic overall. These deeper soils are well drained with strong desilication and thus are allophanic, generating Typic Hapludands. Ubiquitous redox features, together with short-lived contemporary reduction observed in the lower coverbed of a Kainui soil profile, indicate that the Kainui soil in general is likely to be saturated by perching for several days, or near saturation for several months, each year. The perching occurs because the coverbed overlies a slowly-permeable, buried, clay-rich paleosol on upper Hamilton Ash beds, >c. 50 ka in age, which makes up the lower part of the two-storeyed Kainui soil. The coverbed-paleosol boundary is a lithologic discontinuity (unconformity). Irregular in shape, it represents a tree-overturn paleosurface that may be c. 74 ka in age (MOIS 5/4 boundary). The buried paleosol is markedly altered and halloysitic with relict clay skins (forming paleo-argillic and/or paleo-kandic horizons) and redoximorphic features. It is inferred to have formed via developmental upbuilding pedogenesis during the Last Interglacial (MOIS 5e). The entire Hamilton Ash sequence, c. 3 m in thickness and overlain unconformably by Rotoehu Ash and underlain by c. 340-ka Rangitawa Tephra at the base, represents a thick composite (accretionary) set of clayey, welded paleosols developed by upbuilding pedogenesis from MOIS 10 to 5.

year: 2019

title: Magnetic energy release in dynamic fan reconnection models

authors: Craig, Ian J.D.

subjects: MHD—plasmas—sun

abstract: The problem of dynamic, three-dimensional magnetic reconnection is considered. Analytic “fan current” solutions are derived by superposing plane-wave disturbances on magnetic X-point equilibria. The localization of the wave produces a strong current sheet containing the neutral point. It is shown that the classical rate of resistive dissipation in the sheet, namely Wn~n1/2, represents the slowest possible energy-loss rate for the disturbance. The conditions required for fast coronal reconnection are then discussed. It is pointed out that significant “flare-like” energy release may be possible under physically realizable conditions. Moreover, the small length scales associated with the current sheet widths of order ∆x~n1/2 suggest that conditions are probably collisionless close to the neutral point. It is argued that our results are consistent with magnetic reconnection simulations that display “stalling” of the merging rate at small plasma resistivities.

text: Magnetic energy release in dynamic fan reconnection models The problem of dynamic, three-dimensional magnetic reconnection is considered. Analytic “fan current” solutions are derived by superposing plane-wave disturbances on magnetic X-point equilibria. The localization of the wave produces a strong current sheet containing the neutral point. It is shown that the classical rate of resistive dissipation in the sheet, namely Wn~n1/2, represents the slowest possible energy-loss rate for the disturbance. The conditions required for fast coronal reconnection are then discussed. It is pointed out that significant “flare-like” energy release may be possible under physically realizable conditions. Moreover, the small length scales associated with the current sheet widths of order ∆x~n1/2 suggest that conditions are probably collisionless close to the neutral point. It is argued that our results are consistent with magnetic reconnection simulations that display “stalling” of the merging rate at small plasma resistivities.

year: 1999-01

title: Te Karauna Hou: the senior Ngati Rahiri rangatira

authors: Hart, Philip

abstract: Te Karauna Hou, the principal Ngati Rahiri rangatira living at Te Aroha in 1880, had a distinguished whakapapa linking him to several hapu. Before settling permanently at Te Aroha in the 1870s he lived in several places, especially at Kaitawa, on the southern outskirts of Thames. One of the principal rangatira in Hauraki, he was loyal to the Crown during the Waikato War, and later assisted Pakeha settlement. To emphasize his mana and that of his hapu, he held big festivities at Kaitawa and at Omahu pa at Te Aroha. 
In 1871, when Ngati Haua won a (temporary) victory in the land court over the ownership of the Aroha Block, Karauna took control of it on behalf of the Marutuahu confederation, and subsequently kept Ngati Haua at bay. For a time he opposed road-making on this block, but later agreed to it, for financial reasons. Like all rangatira, he sought to maximize his ownership of as many blocks of land as possible, sometimes having his lies exposed through his contradicting his earlier evidence. He also denied receiving money for land when his denials were easily disproved. Despite leasing and selling land, selling timber and gum, and opening his land to miners, he often struggled financially.  
Karauna claimed to have found gold in Hauraki in 1852, and was willing to open his land at Thames to miners, but did not invest in any claims before the Te Aroha rush, when he attempted to extract a bonus of £1,000 from the government for opening the field. After his death in 1885, Pakeha remembered with gratitude his friendly attitude to them, but they also remembered his drunkenness, which meant he lost the respect of both Maori and Pakeha in his latter years.

text: Te Karauna Hou: the senior Ngati Rahiri rangatira Te Karauna Hou, the principal Ngati Rahiri rangatira living at Te Aroha in 1880, had a distinguished whakapapa linking him to several hapu. Before settling permanently at Te Aroha in the 1870s he lived in several places, especially at Kaitawa, on the southern outskirts of Thames. One of the principal rangatira in Hauraki, he was loyal to the Crown during the Waikato War, and later assisted Pakeha settlement. To emphasize his mana and that of his hapu, he held big festivities at Kaitawa and at Omahu pa at Te Aroha. 
In 1871, when Ngati Haua won a (temporary) victory in the land court over the ownership of the Aroha Block, Karauna took control of it on behalf of the Marutuahu confederation, and subsequently kept Ngati Haua at bay. For a time he opposed road-making on this block, but later agreed to it, for financial reasons. Like all rangatira, he sought to maximize his ownership of as many blocks of land as possible, sometimes having his lies exposed through his contradicting his earlier evidence. He also denied receiving money for land when his denials were easily disproved. Despite leasing and selling land, selling timber and gum, and opening his land to miners, he often struggled financially.  
Karauna claimed to have found gold in Hauraki in 1852, and was willing to open his land at Thames to miners, but did not invest in any claims before the Te Aroha rush, when he attempted to extract a bonus of £1,000 from the government for opening the field. After his death in 1885, Pakeha remembered with gratitude his friendly attitude to them, but they also remembered his drunkenness, which meant he lost the respect of both Maori and Pakeha in his latter years.

year: 2016