Bruce W. Hayward A Field Guide Volcanoes Bruce W. Hayward Aerial photography by of Auckland Alastair Jamieson Contents Introduction 1 Auckland Volcanic Field 2 How the volcanoes work 4 Wet explosive eruptions 4 Fire-fountaining and fiery explosive eruptions 6 Lava flows 8 Volcanic bombs and projectile blocks 11 Volcanic ‘hailstones’ 13 Lava caves 13 How old is each volcano? 16 Eruptions and sea level 24 Auckland’s next eruption? 26 The magma below Auckland 26 Time and place of Auckland’s next eruption 28 Monitoring for volcanic activity 30 The next eruption – what to expect 32 DEVORA 34 Auckland Lifelines Group 34 Human interaction with Auckland’s volcanoes 35 Māori occupation and use of Auckland’s volcanoes 35 Volcanoes as water sources 39 Volcanoes lost and damaged 42 Tūpuna Maunga Authority 44 Volcanoes of the Waitematā Harbour and North Shore 46 1. Rangitoto 48 2. Motukorea/Browns Island 62 3. Pupuke Moana/Pupuke Volcano 70 Northcote Road volcanic sequence 75 Takapuna Fossil Forest and Takapuna–Milford Coastal Walk 77 4. Te Kopua-o-Matakamokamo/Tank Farm/Tuff Crater 82 5. Te Kopua-o-Matakerepo/Onepoto Basin 86 6. Maungauika/North Head 90 7. Takarunga/Mt Victoria 96 8. Takararo/Mt Cambria 102 Volcanoes of central Auckland 104 9. Albert Park Volcano 106 10. Grafton Volcano 108 11. Pukekawa/Auckland Domain 112 12. Te Pou Hawaiki 116 13. Maungawhau/Mt Eden 118 14. Ōhinerangi/Mt Hobson/Ōhinerau 124 15. Te Kōpuke/Tītīkōpuke/Mt St John 128 Meola Reef Te Tokaroa 131 16. Maungakiekie/One Tree Hill 134 Hochstetter Pond and Puka Street Grotto 144 17. Te Tātua-a-Riukiuta/Three Kings 146 Liverpool Street tuff 151 18. Puketāpapa/Pukewīwī/Mt Roskill 152 19. Te Ahi-kā-a-Rakataura/Ōwairaka/Mt Albert 156 20. Te Hopua-a-Rangi/Gloucester Park 162 21. Rarotonga/Mt Smart 166 22. Ōrākei Basin 170 23. Maungarahiri/Little Rangitoto 176 Volcanoes of eastern Auckland 180 24. Whakamuhu/Glover Park/St Heliers 182 25. Taurere/Taylors Hill 186 26. Te Tauoma/Purchas Hill 190 27. Maungarei/Mt Wellington 194 Maungarei Stonefields Reserve and Heritage Trail 201 Waiatarua and Michaels Ave Reserve lava-flow- dammed lake and swamp 203 28. Te Kopua Kai-a-Hiku/Panmure Basin 204 29. Ōhuiarangi/Pigeon Mountain 208 East Tāmaki volcanoes 212 30. Styaks Swamp Crater 214 31. Matanginui/Green Mount 216 32. Te Puke-o-Taramainuku/Ōtara Hill 218 33. Hampton Park Volcano 220 34. Pukewairiki/Highbrook Park 224 35. Te Apunga-o-Tainui/McLennan Hills 228 36. Ōtāhuhu/Mt Richmond 232 37. Mt Robertson/Sturges Park 236 Volcanoes of southern Auckland 240 38. Boggust Park Crater 242 39. Te Pane-o-Mataaho/Māngere Mountain 244 Kiwi Esplanade pahoehoe flows 249 Ambury Regional Park lava flows 250 40. Māngere Lagoon 254 41. Te Motu-a-Hiaroa/Puketūtū 258 42. Moerangi/Waitomokia/Mt Gabriel 264 43. Puketapapakanga-a-Hape/Pukeiti 268 44. Ōtuataua 272 45. Maungataketake/Elletts Mountain 276 Ihumātao Fossil Forest 280 46. Te Pūkaki Tapu-o-Poutukeka/Pūkaki Lagoon 282 47. Crater Hill 286 48. Kohuora Crater 290 49. Cemetery Crater 294 50. Ash Hill Crater 296 51. Te Manurewa-o-Tamapahore/Matukutūruru/Wiri Mountain 298 Wiri Lava Cave 302 52. Matukutūreia/McLaughlins Mountain 304 53. Puhinui Craters 308 Historic basalt buildings of Auckland 310 Glossary 319 Select bibliography 322 Acknowledgements 326 Index 327 m Maungarei/Mt Wellington scoria cone from the southwest in 2018. Photo by Alastair Jamieson Auckland Volcanic Field Most people think of a volcano as a single large a different location and build a relatively small cone that has built up by a series of eruptions volcano that never erupts again. Volcanoes of over a lifetime of thousands to hundreds of this type erupt for a few days to several years thousands of years. All the iconic cone volcanoes and are separated by hundreds to thousands of of the world are of this kind and include most years of inactivity. They tend to erupt within a of New Zealand’s best-known volcanoes, such discrete area that is called a volcanic field and the as Mts Taranaki, Ruapehu, Ngāuruhoe and Auckland Volcanic Field is a classic example. In Whakaari/White Island. Over time, this type of these volcanic fields the magma composition is volcano erupts a considerable amount of lava consistently basalt. Volcanic fields with numerous and ash, often from a single vent at the centre of small centres that each erupted once are called the cone. They all have a magma chamber at a monogenetic. The exact number of volcanoes relatively shallow depth (5–10 km) beneath them in the Auckland Volcanic Field depends on how that periodically clears its throat and erupts part they are counted, as some cones and craters are of its contents at the surface. clustered close together and can be counted Another type of volcanism occurs where there separately or in combination. This book recog- is no magma chamber in the crust but, periodi- nises 53 individual volcanoes. cally, relatively small quantities of molten mantle The Auckland Volcanic Field has erupted rock rise from depths of 60–90 km and erupt at spasmodically over the last 200,000 years. the surface. Each of these eruptions surface in While it is currently dormant, the last eruption, 2 o The best-known symbol or icon Rangitoto, was only around 600 years ago and of Auckland City is Rangitoto Island the field is considered to be still alive and likely – the youngest and largest volcano to erupt again. All of Auckland’s volcanoes, in the Auckland Volcanic Field. except Rangitoto, erupted on land. Sometimes q Motukorea/Browns Island is a combination of volcanic the lava probably set the surrounding forest on landforms (tuff ring, scoria cone, fire but any evidence of this has disappeared. lava flows) produced by all three Each volcano would have killed the native forest styles of eruption that characterise in the immediate vicinity, and in several places Auckland’s volcanoes. Photo by the remains of these forests are buried and Alastair Jamieson preserved by volcanic ash or lava flows. The two best and most easily viewed examples are at Takapuna Reef and at the end of Renton Rd, near Auckland Airport. 3 How the volcanoes work The styles of eruption, types of rock produced and resulting landforms in Auckland’s Volcanic Field ERUPTION STYLE SCIENTIFIC TERM ROCK PRODUCED LANDFORM Phreatomagmatic, Tuff (hardened volcanic Explosion crater (maar), Wet explosive Surtseyan & phreatic ash), tuff breccia tuff cone or tuff ring Fire-fountaining & fiery Scoria (lapilli, cinders), Scoria cone Hawaiian & Strombolian explosive spatter, volcanic bombs (cinder cone) Lava flow, lava field, Lava outpouring Strombolian & Hawaiian Basaltic lava or small lava shield Wet explosive eruptions These eruptions are called phreatomagmatic When many of Auckland’s volcanoes first as they involve both steam and magma. They erupted, the rising magma came into contact with result in the upwards and outwards ejection of a near-surface groundwater in aquifers or swampy rapidly expanding cloud of steam, magmatic gas, ground. Initially, the heat from the extremely hot fragmented lava and other pieces of rock from magma (about 1000–1200 ˚C) caused the water the vent walls. to flash to steam, resulting in a violent explosion, The solid particles that erupted into the rather like what happens when cold water is air and were deposited over the ground are splashed into a pan of extremely hot oil. These referred to by the general term tephra. Tephra first explosive eruptions may have involved only is divided on the basis of particle size into ash steam and are referred to as phreatic or steam (fragments smaller than 2 mm), lapilli (2–64 mm eruptions. The steam blasted up through the across), and blocks and bombs (greater than overlying ground, throwing out large and small 64 mm). Wet explosive eruption columns rose fragments of rock and soil and creating a small to heights of a kilometre or more and the less crater. Deposits from these kinds of eruption dense volcanic ash and lapilli within them were are often structureless heaps of angular blocks dispersed by the wind. in a matrix of finely comminuted soil and rock Fallout tephra accumulated on the ground (known as tuff breccia). on the downwind side of the volcano. Blocks of Commonly, but not always, the steam blast solid rock were ejected from the vent on ballistic eruptions were followed by those that also trajectories and landed nearby. Around the involved the rising magma, the surface of which denser base of the eruption column, base surges was instantly chilled, solidified and explosively of superheated steam, gas, ash and lapilli were fragmented when it encountered the cold water. blasted out sideways at speeds up to 200 km/h. 4 o Cartoon of a wet explosive eruption from an Auckland volcano. This style of eruption typically forms an explosion crater surrounded by a tuff ring composed of hardened layers of volcanic ash. Illustration by Margaret Morley These turbulent base surges devastated and partly buried areas within 3–5 km of the vent and were the most dangerous style of eruption produced by Auckland’s volcanoes. As these surges passed they commonly left behind wavy beds of fine ash, sometimes with cross-bedded dune forms. Wet explosive eruptions usually come in a series of pulsating episodes interspersed by short periods of inactivity. These eruptions typically produced a relatively shallow (50–100 m deep), wide (200–1000 m across), circular explosion crater surrounded by a low ring of bedded m Part of a sea cliff on Motukorea/Browns Island showing volcanic ash and lapilli. The ash and lapilli bedded tuff. Each layer represents an explosive pulse.