Geo Junkets: New Zealand , North Island (Part 2)
Jesse Garnett White (USA)
The Waipoua Forest and Parataiko Range
I viewed the tilted volcanic outcrops of early Miocene Waipoua Basalt above the Waimamaku River (Fig. 1), then drove into the small town of Waimamaku. I saw a backpacker standing on the sidewalk thumbing a ride holding a paperback in her left hand. She had freckles, black-rimmed glasses, and long blonde dreadlocks. Unrolling my window as I pulled the vehicle over, she walked up to the car, “Can I put my stuff in the back seat and sit up front with you?”. “Absolutely!” I replied. She tossed her hefty pack inside, hopped into the front seat, looked me directly in the eyes, and asked, “Where are you heading?” Reaching out to shake her hand, I finally managed to reply, “I have no idea! My name is Jesse.” “My name is Clear. I am going into the Waipoua Kauri Forest and then hope to get south of Auckland.” And so it was that we decided to stick together until it was time to part and that is exactly what we did.
We visited Tane Mahuta (The Giant Kauri Tree) in the Waipoua Forest. Joining a busload of German tourists, we walked through disinfecting stations (Fig. 2) where the soles of our shoes were scrubbed down and sprayed with disinfectant.
Tane Mahuta was immense (Fig. 3). The girth of the trunk, height and sprawling canopy signified what an entire forest of ancient Kauri must have looked like prior to colonisation. Now the forest is filled with skeletons of dead Kauri and Tane Mahuta is also at risk of dying.
The Waipoua Kauri Forest is part and parcel of the single largest, near-pristine forest tract left in Northland in New Zealand. Designated as a sanctuary in 1952, it is located within the heavily forested Parataiko Range (0 to 580m), a dissected plateau formed on deeply weathered, Lower Miocene Waipoua Subgroup basalt flows and coeval Miocene sediments (15.97 to 20.44 Ma). Outcrops of Waipoua Basalt cover 500km2 of western Northland. Between Kaihu and the Waimamaku valley, the formation consists of lava flows, tephra deposits and lapilli intruded by glomeroporphyritic plagioclase-olivine-augite basalt dike swarms.
Near Kaihu, the Whatoro Breccia Member consists of various igneous lithologies and Waipoua Basalt clasts in a brown tuffaceous matrix (Wright, 1980). The basalts were partially mapped by Harrington (1944) and Hay (1960), but Thompson (1961) was the first to compile a geological map, designate the type locality and name the Waipoua Basalt. Hayward (1972; 1973; 1975) and McFarlan (1974) investigated coastal outcrops mapped in greater detail by Wright (1977), including Maunganui Bluff (Wright, 1980).
Composed of lava flows, pyroclastic deposits, volcanic breccia, dikes and breccia dikes, the Waipoua Basalt extends inland 20km from the coast forming the south-westward tilted Tutamoe Plateau. It’s hypothesised to have erupted subaerially from an unlocated vent or vents. There isn’t any evidence that dike swarms produced significant amounts of lava and any indication of onshore scoria cones or eruptive sites have been eroded. Based on geological evidence, the closest point to a principle source area indicates that the basalts originated from an offshore location, west of Maunganui Bluff, coinciding with large positive gravity and magnetic anomalies.
Hatherton et al (1979) hypothesised that these anomalies are associated with an Eocene seamount. That being conjecture, apart from the spatial coincidence, confirmation and consensus is lacking for the source of the basalts. Geological evidence for an offshore source includes: thinning of basalts, tephra and decrease in grain size away from Maunganui Bluff, increasing quantity of dikes and gravity and magnetic anomalies near the bluff, and the underfit beheaded Waitapu valley (Wright, 1980).
The importance of erosive soils derived over time from these Miocene igneous outcrops cannot be understated. Their placement and subsequent erosion gave rise to the Waipoua forest diversity, Kauri stands and soil sites of international importance. Containing a diverse range of brown angular clays beneath indigenous vegetation, uncommon soil types including Hihi, Aaipoua, Katui, Parataiko, and Waimamaku (Arand et al, 1993) contribute to soil fertility and a species-rich and healthy forest. Kauri also has a considerable influence on soil environment, modifying available nutrient levels and soil moisture regimes (Verkaik and Braakhekke, 2007; Verkaik et al, 2007). Leaf litter, reproductive structures and bark flakes shed by individual Kauri, along with a slow decomposition rate (Enright and Ogden, 1987), lead to the formation of an organic layer that can be two to three metres deep, beneath mature specimens (Silvester, 2000).
Gibbs Farm, Auckland Geohazards and the Coromandel Peninsula
Leaving Tane Mahuta and Waipoua forest, we drove the long and winding Highway 12 to Highway 1. Rounding a corner on the Kaipara Coast Highway, I saw massive sculptures on the hillsides belonging to the eccentric billionaire, Alan Gibbs (Gibbs Farm; Fig. 4).
There didn’t seem to be a public entrance into the compound and all the gates were shut and locked. In a last-ditch effort, I turned up a gravel road for a better vantage point only to find another locked gate. We could see the humongous sculptures, fountains and outbuildings, and considered jumping the fence for a better look. As we contemplated trespassing, a large dual-trailer dump truck pulled up behind us. High in the cab with one arm hanging out the window, I asked the trucker (Peter), “Can we jump in with you for a better look?” “No bother, hop on in!” he replied. He drove us deep into the farm delivering the 28 tons of gravel, then dropped us back off on the way out.
The largest urban area in the country, the choked stop-and-go traffic on the motorways around Auckland are a bear. A landscape of subdued rolling hills over weathered basement Mesozoic greywacke overlain by Late Eocene to Early Miocene marine sediments and volcaniclastics makes up for the congestion. Marred by small volcanic cones, it’s easy to visualise past and potential effects of local volcanic, regional seismic, and tsunami related hazards around the city (Edbrooke et al, 2003). There is little doubt that future volcanic eruptions will occur with serious consequences for the city of Auckland.
The Auckland Volcanic Field (AVF) documents repeated and varied eruptions, with the most recent occurring approximately 600 years ago. The tsunami risk is also daunting, with at least one tsunami occurring every ten years along the coasts of New Zealand, with wave height greater than one meter. Troubling for Auckland is the tsunami hazard posed by the Kermadec Trench and southern New Hebrides Trench subduction zone (Power et al, 2013). The more exposed northern section of the east coast and outer islands in the Hauraki Gulf face the greatest hazard from regional tsunamis in the Auckland region (Lane et al, 2013).
Once through the city, it was clear sailing. We ate clear-made cheese and Tabasco sandwiches on white bread on our way to the Coromandel Peninsula, specifically Whitianga for the night. Driving from Auckland to Whitianga, we passed through the AVF, Huaraki Rift and Huaraki (Coromandel) Volcanic Zone (CVZ).
The changing tectonic regimes from convergent, passive, to extensional are reflected in four major North Island volcanic fields that developed in distinct tectonic settings at different times. These include Cenozoic arc volcanism in the Huaraki CVZ and Hauraki Rift, AVF intraplate basaltic volcanism and extensional arc volcanism of the Taupo Volcanic Zone (TVZ).
Late Oligocene subduction-related tectonics at the Australian-Pacific plate boundary produced andesite-dacite dominated volcanic island arc systems in what is now the North Island. CVZ magmatism and subsequent eruptions began in the early Miocene, followed by basaltic-rhyolitic volcanism associated with plate boundary migration and extension (Balance, 1976; Nicholson et al, 2004). CVZ volcanism continued until late Pliocene, before shifting south to the TVZ (Carter et al, 2003). CSV volcanic rocks and coeval volcaniclastics are divided into the Coromandel Group, Whitianga Group and Mercury basalt. Primarily calc-alkaline, these units overlie Manaia Hill Group Late Jurassic greywacke and argillite (Skinner, 1986).
The following morning, we left for a Department of Conservation (DOC) bunkhouse at Fletcher Bay. We’d considered going to the geothermal Hot Water Beach (HWB) but low tide wasn’t until 3:50pm and decided not to wait around. The thermal seeps at HWB flow from the Wharepapa Ignimbrite (5 to 6 Ma) and are associated with an NNE trending fracture zone and regional hot spring systems of the Coromandel Peninsula and Great Barrier Island. Cooling upper crustal rocks are the presumed heat source, with deep fluid temperatures reaching 170°C (Hochstein et al, 1996; Skinner, 1995). Seepages occur in five localities aligned over a distance of half a kilometre. The northern-most seep is under the ocean but the HWB seeps are between high and low tide level. Hot water discharges at numerous exit points over 15m (Hochstein et al, 1996).
The landscapes between Whitianga and Colville were mesmerising, as we drove the twisting roads around cliffs, mountain passes, estuaries and beaches (Figs. 5 and 6). Just out of Colville, we followed a cattle dog forcing cows down the road, herding them with ease. Once past the herd, we drove a gravel track that would be one of the prettiest drives I have ever witnessed. It follows the western shoreline, where the Moehau Range (Sleeping Wind) rises steeply from the sea (Fig. 7).
The range is composed of Upper Jurassic greywacke, intruded by dikes and plugs of porphyritic andesite and dacite (Kai-iti Porphyrites), and plutons of granodiorite and quartz-diorite (Paritu Plutonics). The greywacke is intensely deformed, due to late Mesozoic folding superimposed by Paritu intrusions rife with porphyritic intrusions (Skinner, 1975).
Views from the road between Colville and Fletcher Bay are stunning. There are no guard rails and the precipitous drops are truly life-ending. The coastline, mountains and flora made us delirious with happiness. Arriving at Fletcher Bay, we met the caretaker – a lovely lady named Heather. She gave us the entire bunkhouse. Excellent exposures of the Miocene Waitemata Group (altered volcanic glass), Colville Formation and Port Charles Andesite crop out at Fletcher Bay. The Colville is a fine-grained, thin-bedded flysch, composed of analcime in a matrix of andesite grit (Ballance, 1976a; Balance 1976b), basal conglomerate, calcareous sandstone, and lithic volcanic sandstone and siltstone over meta-greywacke. The Port Charles Andesite consists of hypersthene, augite and hornblende andesite flows (Skinner, 1967; Christie et al, 2002).
The next morning, I woke up refreshed, shook the dust off and watched a cowboy reign in cattle from the hillside with his dogs. They forced the cows down the trampled terraced hills into pens. A lone bull wasn’t having any of it and bore down on the dogs. The cowboy sent another dog running to assist. I watched it jump over a 2m fence with ease. Working as a team, the four dogs got the bull moving by nipping at its nose and ankles, pushing it towards the pens.
After breakfast, we drove to Tairua through Te Kouma, Te Mata and Tapu, through the mountains to Coroglen. The views of Wanganui Island, coastline and forests were incredible. On arrival at Hahei Beach, we swam in and floated on the rolling waves for hours. Hahei Beach is at the northern end of a belt of Whitianga Group acidic volcanic rocks (Schofield, 1967), subdivided into the Minden Rhyolite Subgroup and Coroglen Subgroup (Thompson, 1966; Hayward, 1974a, 1974b; Rabone, 1975; Skinner, 1976; and Moore 1979). The Whitianga Group at Hahei consists of breccia, lapilli breccia and tuff (Coroglen Subgroup), overlain by rhyolite lava domes (Minden Rhyolite Subgroup). Pyroclastic sediments were erupted in Late Miocene to pre-Pliocene, followed by the formation of Late Miocene rhyolite domes (Moore, 1983).
After a long soak in the waves, we drove to a crystal shop in Tairua, where I purchased two New Zealand Greenstone necklaces for Clear and me. Later, we found a thin strip of rocky beach near the mouth of the Tairua Estuary beneath Paku Hill (Fig. 8). There were thousands of wonderful colorful shells, including gastropods and bivalves.
That evening, I walked onto the sands of the upper estuary as the sun cast light on Paku Hill (Fig. 9) from behind the Coromandel Forest Park (Fig. 10).
The exposed estuary sand waves (Fig. 11) and stranded tide pools were crawling with gastropods.
Near the shoreline, the sand was dotted with hundreds of thousands of sand-crab burrows and trackways (Fig. 12).
Kohioawa Beach (and further non-geo hazards) and Putauaki Volcano
The following morning, I dropped Clear off in Paeroa, then forged onward towards Opatiki. I stopped for a swim at Kohioawa Beach, where I nearly lost my life. The surf looked super rough but I didn’t really care. I took off all of my clothes, piled them on the beach and got into the water. I waded out ankle deep, shin deep and then knee deep when a massive creeper wave came out of nowhere. The sand under my feet scooped out from under me pulling me under water and upside down. I felt my head and shoulder scrape the sand. When I surfaced, I had been sucked out beyond the breakers into the rollers. I could see people casting fishing lines out into the water on either side, but they were so far away and yelling wouldn’t do any good. I just did what anyone caught in a rip is supposed to do and started swimming parallel to the beach.
Naked and swimming sideways, I eventually crossed back over the breakers. I was so tired, I just let the waves push me back towards shore. Once I could get my feet, I tried to stand up but got pounded face first into the sand. Then I don’t remember anything until I woke up with the water lapping my legs and torso. I had sand in my ears, eyes, nose, on my face and in my hair. Sprawled prostrate on the beach, I had no idea what the hell was going on, but I could see my clothes about 100m away. I got up and started walking towards them like some kind of sun-burned sea-creature with man boobs and a bloated fish-filled belly.
Back in the car with all limbs still attached, I started towards Taupo. The views of Putauaki Volcano (Mount Edgecumbe) from State Highway 2 were stellar (Fig. 13).
Located near the eastern boundary of the Taupo Volcanic Zone (TVZ), it is situated on the south-eastern flank of the Whakatane Graben in the Bay of Plenty region (Nairn and Beanland, 1989). Putauaki is a dormant, steep sided, vegetation covered, multiple vent andesite-dacite composite cone (Duncan 1970; Nairn 1995; Wilson et al, 1995), with the last known eruption occurring 1,850 years ago. There are two craters on the summit, separated by a narrow ridge. The western crater contains a brackish lake but the eastern crater is deep and dry. There are also two craters on the lower flanks and a small incipient cone on the north side.
Stay tuned for GeoJunkets: New Zealand – Part 3, covering the Wairakei–Tauhara Geothermal Fields in the TVZ, Lake Taupo, Huka Falls (Fig. 14), Craters of the Moon Geothermal Area, New Plymouth, and Wellington and surrounding areas.
|The parts in this series comprise:|
|Geo Junkets: New Zealand, North Island (Part 1)|
|Geo Junkets: New Zealand, North Island (Part 2)|
|Geo Junkets: New Zealand, North Island (Part 3)|
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