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3 The consequences of the powerful Taupo eruption of c. AD 232, showing the position of the vent, now submerged under Lake Taupo; the area covered by ashfall to a depth of 10 cm or more, with thickness contours (isopachs) in centimetres; the final extent of deposits from the extremely energetic pyroclastic flow, which spread a layer of loose ignimbrite across 20,000 km 2 , covering all neighbouring 

3 The consequences of the powerful Taupo eruption of c. AD 232, showing the position of the vent, now submerged under Lake Taupo; the area covered by ashfall to a depth of 10 cm or more, with thickness contours (isopachs) in centimetres; the final extent of deposits from the extremely energetic pyroclastic flow, which spread a layer of loose ignimbrite across 20,000 km 2 , covering all neighbouring 

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This chapter introduces the story of Pureora Forest Park (PFP), in the central North Island, New Zealand, by describing the extremely violent Taupo eruption of c. AD 232 and its consequences for the surrounding forests and mountains. It gives a broad-scale local geological history, detailing the origins of some important local sedimentary rocks and...

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Context 1
... were erupted from Mangakino caldera, referred to collectively as Pakaumanu Group (Briggs et al. 1993; Leonard et al. 2010) [3, 19]. Mangakino caldera has since been completely infilled by rhyolite lava domes. The ignimbrite cap on flat-topped Hikurangi is the Mangakino-derived Ongatiti ignimbrite, aged c. 1.23 Mya (Edbrooke 2005) 5]. Later, the large Whakamaru caldera, which lies north of Lake Taupo, erupted pyroclastic materials in an episode of intense volcanism, generating Whakamaru Group ignimbrites around 350,000 years ago. The Whakamaru 1 and 2 ignimbrites comprise about 1500 and 500 km 3 of eruptive material (volumes are given as ‘dense rock equivalent’ , DRE), respectively (Wilson et al. 2009) [50]. Both therefore qualify as products of so- called ‘super - eruption’ volcanic events (Wilson 2008) [49]. The Whakamaru ignimbrites are very extensive in the Pureora area (including much of the park), both west and east of Lake Taupo, and further north in the Tokoroa area (Leonard et al. 2010) [19]. The next major event was the Oruanui eruption, another ‘super - eruption’ episode at Taupo volcano, which generated about 530 km 3 of material (DRE) or 1170 km 3 as loose material (Wilson 2001) [48]. Also known as the Kawakawa eruption, the event is dated to c. 25,400 years ago (Vandergoes et al. 2013) [39]. The complex eruption produced a number of pyroclastic flow deposits, everywhere soft and non-welded (i.e. they comprise pumice clasts in a coarse ash matrix), known as Oruanui ignimbrite. In addition, fall deposits were blown at least 1500 km beyond the New Zealand archipelago. The Oruanui ignimbrite is found both to the northeast and southeast of the Pureora area, and it is extensive around the flanks of Taupo volcano (Leonard et al. 2010; Wilson 2001) [19, 48]. The Oruanui eruption was centred on the northern part of modern-day Lake Taupo (including Western Bay), and formed a large, 35-km-wide elliptical caldera forming the modern shape of the northern lake. The Waikato River, which for tens of millennia had flowed north across the Hauraki Plains into the Firth of Thames and beyond, was diverted westward into the Hamilton Basin around 22,000 years ago, partly because volcaniclastic debris from the Oruanui eruption washed down and eventually blocked the river at Piarere, near the junction of SH1 and SH 29 (Manville and Wilson 2004; McCraw 2011; Selby and Lowe 1992) 23, 27, 33]. Since the Oruanui/Kawakawa eruption, Taupo volcano has erupted a further 28 times, most recently as the so-called Taupo eruption (Wilson 1993; Wilson et al. 2009) [47, 50]. Rhyolitic ash materials from many of these 28 eruptions, and also equivalent distal deposits from rhyolitic eruptions in the Okataina Volcanic Centre near Rotorua , would have blanketed or ‘dusted’ the Pureora area when wind directions were suitable. At the same time, the andesitic volcanoes of Tongariro Volcanic Centre to the southeast of Pureora (Ruapehu, Ngauruhoe, Tongariro) have also been active, erupting very frequently since the earliest events dating back to c. 275,000 years ago (Lee et al. 2011) [17]. Multiple, thin, andesitic ash beds of varying thickness, often only a few millimetres or so, were frequently deposited on the Hauhungaroa and southern Rangitoto Ranges. Several prominent andesitic ash-bed deposits of Holocene age (the Holocene comprises the past 11,700 years) derived from volcanoes in the Tongariro Volcanic Centre include the Mangamate tephra (erupted c. 11,200 years ago), Papakai tephra (c. 5000 years ago), and Mangatawai tephra (c. 3000 years ago). Occasionally, ash from Mt Taranaki (Egmont volcano), which began activity about 130,000 years ago (Townsend et al. 2008) [38], was blown as far east as Pureora and beyond, one recent thin bed being the Burrell ash (c. AD 1655) (Moebis et al. 2011) [28]. The most recent eruptions of the area (since the Taupo eruption), and their effects on Maori society, are summarised by Lowe et al. (2002) [21]. The complex Taupo eruption sequence of c. AD 232 has been divided into seven phases. The products of each are described as subunits Y1 to Y7 of unit Y by Wilson (Wilson 1993; Wilson and Walker 1985) [46, 47]. The eruption was centred on vents near the now-submerged Horomatangi Reefs in the northeastern part of Lake Taupo (Fig. 1.3). Four eruptions of varying character and eruption style, generating Initial ash (subunit Y1), Hatepe plinian (Y2), Hatepe ash (Y3), and Rotongaio ash (Y4) took place, the wide variations relating to differences in discharge rate and the degree of interaction between the magma and water in proto-Lake Taupo and from rainstorms (Wilson 1985; Wilson and Walker 1985) [45, 46]. The fifth event in the sequence, Taupo plinian (Y5), generated a towering column of ash about 35 to 40 km high (Houghton et al. 2015 ) [14] comprising about 23 km 3 of loose material. Ash from this plinian column was blown eastwards across the country well beyond Hawke’s Bay and into the Pacific Ocean (Fig. 1.3). During this phase, minor intraplinian pyroclastic flows were generated near the vent area (Y6). The column then collapsed catastrophically to generate powerful ground-hugging pyroclastic flows (density currents) of hot gas, ash, pumice, crystals, and rock fragments that raced radially outward at speeds of more than 150 m/s (200-300 m/s near the vent) to form the Taupo ignimbrite (Y7), containing at least 30 km 3 of loose material (Wilson 1985) [45]. See Fig. 1.4. The soft Taupo ignimbrite is non-welded, and was emplaced entirely within about 400 seconds (Wilson 1985) [45]. Its temperature was about 380 – 500°C at more than c. 40 km from vents; within c. 30 – 40 km of the vents it was about 150 – 300°C (Hudspith et al. 2010; McClelland et al. 2004) [15, 26]. The extreme violence of the emplacement of Taupo ignimbrite caused the deposit to be spread thinly over the landscape to an average thickness of only c. 1.5 m, and the high energy release (  150 ± 50 megatons of TNT equivalent: Lowe and de Lange 2000) [20], enabled the Taupo ignimbrite to rush over hills and mountains up to c. 1500 m above the vent  no other pyroclastic flow is known to have climbed higher (Francis 1993) [6]  and the only mountain within its range that it did not ascend entirely was Ruapehu itself. That is why the beech trees on the southern and western slopes of Ruapehu were the only ones within 80 km of Taupo to escape complete destruction, and hence survived to spread and re-clothe the central volcanic mountains with beech forests similar to those that grew there before the eruption. It is likely that this climactic ignimbrite-emplacement phase generated an atmospheric shock wave, producing a volcano-meteorological tsunami that reached coastal areas worldwide (Lowe and de Lange 2000) [20]. The total eruptive bulk (loose) volume for the Taupo eruptives has been estimated at c. 105 km 3 (equivalent to c.35 km 3 DRE) (Wilson et al. 2009) [50]. Following the Taupo eruption, Lake Taupo refilled and reached a higher level than today’s, as is evident from the semi-continuous, wave-cut bench and highstand shoreline deposits (Manville et al. 1999; Manville et al. 2007) [22, 24]. Dramatic, sudden failure of a pumiceous pyroclastic dam led to the release of a peak discharge of 20,000  40,000 m 3 /sec. Tonnes of loose pumice and other materials were washed down the Waikato River as a break-out flood event (Manville et al. 2007) [24], choking the river bed and depositing sediment many metres thick along the margins (Thornton 1985) [37]. Pre-existing sediments were cannibalised in part and transported as well as the mainly pumiceous materials. Temporary dams formed on the Ongarue River, followed by flash floods as the dams collapsed (Walker and Cooke 2003) [40]. Riparian terraces formed from the Taupo eruption-derived pumiceous alluvium (known geologically as Taupo Pumice Alluvium) are now common throughout many central North Island waterways (Manville et al. 2009; Nicholls 1986) [25, 30]. The violent emplacement of the Taupo ignimbrite devastated the forests, and charred logs as large as 1 m in diameter may be found in situ close to the vents (Froggatt et al. 1981) [7]. Hudspith et al. (2010) [15]estimated that about 1 km 3 of forest timber was almost instantly incinerated. The degree and nature of vegetation disturbance arising from the Taupo fallout deposits (rather than ignimbrite emplacement) varied according to the thickness of ashfall, local topographical features, and probably the vigour of the forest. Immediately after the eruption, stands of bracken and other seral taxa flourished. Revegetation was complete within about 200 years of the eruption, even at sites overwhelmed by the Taupo ignimbrite (Wilmshurst and McGlone 1996) [43]. Products of most of the main phases of the eruption are shown here. Hatepe plinian, Hatepe ash, Rotongaio ash, and Taupo plinian are all fall deposits, comprising pyroclastic materials blasted into the air that were then blown by the wind to fall over the land surface like a blanketing snowfall. The characteristics of each unit relate in part to the rate of magma eruption and the amount of water entering the vent, so that the ensuing deposits range from coarse pumice clasts (open symbols), small rock fragments (closed symbols), and coarse to fine ash (fine stipple and dashes). The final deposit, Taupo ignimbrite, is the material that was spread across the landscape by the pyroclastic flow generated by the collapse of the towering plinian eruption column (Houghton et al. 2015; Wilson 1985) [14, 45]. The Hatepe ash phase of the eruption was abruptly terminated (possibly when lake water flooded deep into the vent), and running water from torrential rain carved gullies into the deposits (marked by ‘E’, indicating erosion by flowing water). After a break of less than about three weeks (Wilson 1993) [47], fine, dark- grey ‘muddy’ Rotongaio ash, and then pumices of the Taupo plinian phase, were ...
Context 2
... mode of origin. Pyroclastic flows infill valleys forming extensive, thick sheets of fragmental rhyolitic material, and mount ridges forming thin veneer deposits. After deposition, thick, very hot (600-700°C) deposits (such as those infilling valleys) can weld or sinter together to varying degrees of hardness. At one end of the hardness spectrum, some ignimbrites are rock solid (referred to as densely-welded ignimbrite), and at the other end, some can be excavated with a spoon (referred to as weakly welded). Others may be entirely non-welded: for example, Taupo ignimbrite and Oruanui ignimbrite are both non-welded ignimbrites (Smith et al. 2012) [35]. More than a dozen ignimbrites were erupted from Mangakino caldera, referred to collectively as Pakaumanu Group (Briggs et al. 1993; Leonard et al. 2010) [3, 19]. Mangakino caldera has since been completely infilled by rhyolite lava domes. The ignimbrite cap on flat-topped Hikurangi is the Mangakino-derived Ongatiti ignimbrite, aged c. 1.23 Mya (Edbrooke 2005) 5]. Later, the large Whakamaru caldera, which lies north of Lake Taupo, erupted pyroclastic materials in an episode of intense volcanism, generating Whakamaru Group ignimbrites around 350,000 years ago. The Whakamaru 1 and 2 ignimbrites comprise about 1500 and 500 km 3 of eruptive material (volumes are given as ‘dense rock equivalent’ , DRE), respectively (Wilson et al. 2009) [50]. Both therefore qualify as products of so- called ‘super - eruption’ volcanic events (Wilson 2008) [49]. The Whakamaru ignimbrites are very extensive in the Pureora area (including much of the park), both west and east of Lake Taupo, and further north in the Tokoroa area (Leonard et al. 2010) [19]. The next major event was the Oruanui eruption, another ‘super - eruption’ episode at Taupo volcano, which generated about 530 km 3 of material (DRE) or 1170 km 3 as loose material (Wilson 2001) [48]. Also known as the Kawakawa eruption, the event is dated to c. 25,400 years ago (Vandergoes et al. 2013) [39]. The complex eruption produced a number of pyroclastic flow deposits, everywhere soft and non-welded (i.e. they comprise pumice clasts in a coarse ash matrix), known as Oruanui ignimbrite. In addition, fall deposits were blown at least 1500 km beyond the New Zealand archipelago. The Oruanui ignimbrite is found both to the northeast and southeast of the Pureora area, and it is extensive around the flanks of Taupo volcano (Leonard et al. 2010; Wilson 2001) [19, 48]. The Oruanui eruption was centred on the northern part of modern-day Lake Taupo (including Western Bay), and formed a large, 35-km-wide elliptical caldera forming the modern shape of the northern lake. The Waikato River, which for tens of millennia had flowed north across the Hauraki Plains into the Firth of Thames and beyond, was diverted westward into the Hamilton Basin around 22,000 years ago, partly because volcaniclastic debris from the Oruanui eruption washed down and eventually blocked the river at Piarere, near the junction of SH1 and SH 29 (Manville and Wilson 2004; McCraw 2011; Selby and Lowe 1992) 23, 27, 33]. Since the Oruanui/Kawakawa eruption, Taupo volcano has erupted a further 28 times, most recently as the so-called Taupo eruption (Wilson 1993; Wilson et al. 2009) [47, 50]. Rhyolitic ash materials from many of these 28 eruptions, and also equivalent distal deposits from rhyolitic eruptions in the Okataina Volcanic Centre near Rotorua , would have blanketed or ‘dusted’ the Pureora area when wind directions were suitable. At the same time, the andesitic volcanoes of Tongariro Volcanic Centre to the southeast of Pureora (Ruapehu, Ngauruhoe, Tongariro) have also been active, erupting very frequently since the earliest events dating back to c. 275,000 years ago (Lee et al. 2011) [17]. Multiple, thin, andesitic ash beds of varying thickness, often only a few millimetres or so, were frequently deposited on the Hauhungaroa and southern Rangitoto Ranges. Several prominent andesitic ash-bed deposits of Holocene age (the Holocene comprises the past 11,700 years) derived from volcanoes in the Tongariro Volcanic Centre include the Mangamate tephra (erupted c. 11,200 years ago), Papakai tephra (c. 5000 years ago), and Mangatawai tephra (c. 3000 years ago). Occasionally, ash from Mt Taranaki (Egmont volcano), which began activity about 130,000 years ago (Townsend et al. 2008) [38], was blown as far east as Pureora and beyond, one recent thin bed being the Burrell ash (c. AD 1655) (Moebis et al. 2011) [28]. The most recent eruptions of the area (since the Taupo eruption), and their effects on Maori society, are summarised by Lowe et al. (2002) [21]. The complex Taupo eruption sequence of c. AD 232 has been divided into seven phases. The products of each are described as subunits Y1 to Y7 of unit Y by Wilson (Wilson 1993; Wilson and Walker 1985) [46, 47]. The eruption was centred on vents near the now-submerged Horomatangi Reefs in the northeastern part of Lake Taupo (Fig. 1.3). Four eruptions of varying character and eruption style, generating Initial ash (subunit Y1), Hatepe plinian (Y2), Hatepe ash (Y3), and Rotongaio ash (Y4) took place, the wide variations relating to differences in discharge rate and the degree of interaction between the magma and water in proto-Lake Taupo and from rainstorms (Wilson 1985; Wilson and Walker 1985) [45, 46]. The fifth event in the sequence, Taupo plinian (Y5), generated a towering column of ash about 35 to 40 km high (Houghton et al. 2015 ) [14] comprising about 23 km 3 of loose material. Ash from this plinian column was blown eastwards across the country well beyond Hawke’s Bay and into the Pacific Ocean (Fig. 1.3). During this phase, minor intraplinian pyroclastic flows were generated near the vent area (Y6). The column then collapsed catastrophically to generate powerful ground-hugging pyroclastic flows (density currents) of hot gas, ash, pumice, crystals, and rock fragments that raced radially outward at speeds of more than 150 m/s (200-300 m/s near the vent) to form the Taupo ignimbrite (Y7), containing at least 30 km 3 of loose material (Wilson 1985) [45]. See Fig. 1.4. The soft Taupo ignimbrite is non-welded, and was emplaced entirely within about 400 seconds (Wilson 1985) [45]. Its temperature was about 380 – 500°C at more than c. 40 km from vents; within c. 30 – 40 km of the vents it was about 150 – 300°C (Hudspith et al. 2010; McClelland et al. 2004) [15, 26]. The extreme violence of the emplacement of Taupo ignimbrite caused the deposit to be spread thinly over the landscape to an average thickness of only c. 1.5 m, and the high energy release (  150 ± 50 megatons of TNT equivalent: Lowe and de Lange 2000) [20], enabled the Taupo ignimbrite to rush over hills and mountains up to c. 1500 m above the vent  no other pyroclastic flow is known to have climbed higher (Francis 1993) [6]  and the only mountain within its range that it did not ascend entirely was Ruapehu itself. That is why the beech trees on the southern and western slopes of Ruapehu were the only ones within 80 km of Taupo to escape complete destruction, and hence survived to spread and re-clothe the central volcanic mountains with beech forests similar to those that grew there before the eruption. It is likely that this climactic ignimbrite-emplacement phase generated an atmospheric shock wave, producing a volcano-meteorological tsunami that reached coastal areas worldwide (Lowe and de Lange 2000) [20]. The total eruptive bulk (loose) volume for the Taupo eruptives has been estimated at c. 105 km 3 (equivalent to c.35 km 3 DRE) (Wilson et al. 2009) [50]. Following the Taupo eruption, Lake Taupo refilled and reached a higher level than today’s, as is evident from the semi-continuous, wave-cut bench and highstand shoreline deposits (Manville et al. 1999; Manville et al. 2007) [22, 24]. Dramatic, sudden failure of a pumiceous pyroclastic dam led to the release of a peak discharge of 20,000  40,000 m 3 /sec. Tonnes of loose pumice and other materials were washed down the Waikato River as a break-out flood event (Manville et al. 2007) [24], choking the river bed and depositing sediment many metres thick along the margins (Thornton 1985) [37]. Pre-existing sediments were cannibalised in part and transported as well as the mainly pumiceous materials. Temporary dams formed on the Ongarue River, followed by flash floods as the dams collapsed (Walker and Cooke 2003) [40]. Riparian terraces formed from the Taupo eruption-derived pumiceous alluvium (known geologically as Taupo Pumice Alluvium) are now common throughout many central North Island waterways (Manville et al. 2009; Nicholls 1986) [25, 30]. The violent emplacement of the Taupo ignimbrite devastated the forests, and charred logs as large as 1 m in diameter may be found in situ close to the vents (Froggatt et al. 1981) [7]. Hudspith et al. (2010) [15]estimated that about 1 km 3 of forest timber was almost instantly incinerated. The degree and nature of vegetation disturbance arising from the Taupo fallout deposits (rather than ignimbrite emplacement) varied according to the thickness of ashfall, local topographical features, and probably the vigour of the forest. Immediately after the eruption, stands of bracken and other seral taxa flourished. Revegetation was complete within about 200 years of the eruption, even at sites overwhelmed by the Taupo ignimbrite (Wilmshurst and McGlone 1996) [43]. Products of most of the main phases of the eruption are shown here. Hatepe plinian, Hatepe ash, Rotongaio ash, and Taupo plinian are all fall deposits, comprising pyroclastic materials blasted into the air that were then blown by the wind to fall over the land surface like a blanketing snowfall. The characteristics of each unit relate in part to the rate of magma eruption and the amount of water entering the vent, so that the ensuing deposits range from coarse pumice clasts (open symbols), small rock fragments (closed ...

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This thesis considers the transfer and adaptation of Polynesian horticulture to New Zealand through examination of the archaeology of the Waikato Horticultural Complex, an inland horticultural system relying on intensive soil adaptation within a swidden process. The successful transfer and adaptation of Polynesian horticulture, a system developed in the tropics and based on tropical plants, to the temperate climate of New Zealand has long been considered enigmatic with a number of attempts to understand how this was effected. The Waikato Horticultural Complex is characterised by the quarrying and transport of course lithic material to garden sites, often glossed as Maori-made soils, that are recognised as distinct soil types by soil scientists. The Waikato Horticultural Complex presents archaeologically in two similar but distinct aspects indicating two parallel agronomic processes. A multi-disciplinary approach has been followed in examining the Waikato Horticultural Complex. The examination of the Waikato Horticultural Complex occurs at two scales. The first places the horticultural system within the wider regional landscape through understanding its scale and its interaction with that landscape, primarily the soils, geology and vegetation. Secondly the Waikato Horticultural Complex is contextualised with a review of the archaeology of Polynesian horticulture as understood in Eastern Polynesia, along with an examination of the literature describing the 'made soils' phenomena in New Zealand, where it appears to be a strategy distinct within Polynesia. Specifically the nature of the Waikato Horticultural Complex is described and characterised. The data relating to the Waikato Horticultural Complex drawn on for this thesis has been derived from a mass of reporting generated through the Cultural Heritage Management process. Most of this reporting has been created by the author of this thesis. This data describes the collective attributes or features of the Waikato Horticultural Complex, which relate to forest clearance, garden development including the quarrying of course lithic material and the features and context in which it is found following transport to the gardens, crop storage structures along with elements reflecting domestic activities. Data relating to the palaeo-environment, along with plant microfossil data relating to cultigens is reviewed. Questions of depositional processes and function of the transported material within the associated archaeological contexts are central to understanding potential motives for the application of the labour intensive process. As well as 'standard' archaeological techniques two additional approaches have been applied. At the micro-scale, soil micromorphological techniques have been applied to the examination of both manifestations of the made soil phenomenon, which have resolved questions about depositional and post-depositional processes and the presence or absence of relict features from now-destroyed components of the gardens. To further test the role of actual and potential elements of the agronomy employed in relation to the transported material the results from experimental garden plots have also been considered.