There were also "V" formations in the cliff where a section of tuff had collapsed, leaving a clear fault in the strata.
GeoTours
Auckland Volcanic Experience
Auckland Rainforest and Coast
- Stories of the Rocks and Volcanoes.
Discovery 1: Auckland: City of Volcanoes Morning 8am to noon or Afternoon 1pm to 5pm.
Back to Discovery 1
Murray Baker has been running GeoTours since 1995 Murray has a degree in geology and is also very knowledgable about plants, trees and seaweeds which you will see on your tour. He's great at explaining things, and has samples of different kinds of volcanic rocks and ash in the van for you to have a look at. There is also a speaker system in the minivan so he can talk to you about what you are seeing while you are going along.
Our tour went on till 5.30 and we were learning the whole time, with a short break for afternoon tea provided by Murray. This tour is perfect for any overseas visitors who are curious about volcanoes, but it is also fascinating for locals; Daphne and Miriam both learned heaps. So it would be a really good birthday present for someone, or an excursion for you and your visitors.
Our pick up point was opposite the ferry buildings in Quay Street. This is where all the coaches and the AirBus go from, now that the Downtown Airline Terminal has gone. It's really handy for anyone coming across on the ferry. Murray also does hotel pick-ups - when we boarded there were already two passengers on the bus, Larry from America and Eric from China.
We headed out across the bridge, with Murray talking about the general geological history of the Auckland region, and pointing out that the harbour used to be the Waitemata River Valley.
We went first to Tank Farm, with a little bit of social history of the area on the way. Murray had charts and maps to show us how the tuff crater was formed and how it has evolved into its present state, with mangroves covering the now filled-in crater. Where the houses stand, high over the crater, is the tuff ring. Scoria cones and tuff rings can form in a few days.
Murray talked about Rangitoto, Auckland's youngest volcano, and showed us a lava bomb from its eruption. He also had a jar of little lapilli from Mt Wellington, and some very fine ash from the Taupo eruption. Explosion craters throw out tuff; lava fountains produce the bombs, scoria and lapilli, and lava flow solidifies into basalt, either with or without vesicles (little gas bubbles).
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From Tank Farm we went to Lake Pupuke (one of Auckland's oldest volcanic craters), down by Smale's Quarry. On one side of the channel of water leading to the lake there was a big outcrop of basalt. On the other side there was a bank of tuff. In it there was a perfect cross section of the remains of a small volcanic cone, and a huge lava bomb embedded high in the cliff face. There were also "V" formations in the cliff where a section of tuff had collapsed, leaving a clear fault in the strata. |
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| Murray showed us that the bubble holes in the rock are smaller near the top edge, where the gas rises fast while the lava is still molten. As the lava cools and solidifies it is harder for the gas to rise, and the lower bubbles coalesce, leaving larger holes lower down in the rock. All the holes in the rocks are constantly being enlarged by the corrosive action of the salt water.
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Some of the cylindrical tree holes were later filled in with more flowing lava, so that there are casts of the tree branches and trunks. Murray showed us the difference between Pahoehoe lava, with its circular flow marks, and craggy a'a lava. (Larry says it's called a'a because that's what you say when you walk on it, because it's very sharp.) |
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| There are also big flattish holes, gas blisters, where there are tiny "stalactites" formed when the still molten lava dripped from the upper surface of the hole. On the sides of some blisters there are dribble marks like melting butter - but the drips and dribbles are all solid rock. In one place we saw where drips had fallen from the upper surface and lie like little rock straws on the lower surface. We looked at the great big well-like hole where there had been a huge tree (probably kauri) felled by the lava flow, and walked on round to the Takapuna Reef area. Here we saw tuff and lava. The ferrous parts of the tuff have reacted to the chemicals in the salt water and turned rusty coloured. |
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The reef itself is nearly all trees, many of which are casts, so that they look like solid rock. In other places, two trees are so close together that the "neck" of lava around one vanished stump has retained solid lava fused to the next one, making an arch formation. We examined more casts and holes and drips all the way back to the van and then went back across the harbour. First we went to the Domain, another of Auckland's oldest volcanoes. We drove slowly through, with Murray pointing out the shapes of the crater. |
| Then it was into Cornwall Park, where we had our tea stop. (Coffee or any one of several kinds of tea and cold water) On the way up One Tree Hill we passed the Observatory, and Maori fortifications and storage pits. Visitors write their names in rocks at the bottom of the different craters on this mountain, and Murray sees it change daily. Some of the writing is in Japanese. At the top of the hill, by the memorial and the poor tattered tree we looked out over volcanic Auckland, with Murray pointing out all the features as we slowly walked around the summit. The sun was setting by this time and the city looked just beautiful. | 
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Our last stop was at Three Kings, where Murray told us that the gently sloping road we were driving on was formed on the thick layer of tuff ejected from the big crater we could see behind the houses. He led us across the road to where there was a cutting showing about three metres of tuff in many thin layers. All this material had been ejected in a matter of minutes from the eruption. Murray showed us different materials in the layers, including some tiny round things he described as "fossilised raindrops", formed when the rain fell through the ash clouds and became coated until they were solid ash. |
GeoTours runs most days - check in the low season. Bookings are essential.
Murray hands out a printed tour guide with drawings and explanations, a glossary and a bibliography.
As well as the morning or afternoon tours there are full day tours, which include the west coast area, with rainforest and gannets. Tours vary according to weather and tide conditions, so even if you do the same tour as we did, you may see different things. Check out their brochure.
For those wishing to do a longer tour there are tours of 2, 3, or 6 days. These may cover Coromandel, The Central Plateau (Rotorua region or Taupo-Tongariro region), West Coast (North Is), East Coast - Hawkes Bay, or Northland.
by Miriam Beatson 6/00
For price and time details see main page
GeoTours
Murray Baker (Geologist)
Or by phone (06) 3626829
mobile phone (0274) 860771
POST: P.O. Box 494 Levin, New Zealand
Email: murray@geotours.co.nz
© GeoTours, 2000