The caldera wall in almost vertical around its entirity. Here the lava wall towers above the caldera floor on the eastern side of the caldera. Lava units are part of the old main cone sequence. They are conspicuously flow banded.
Another view of the caldera wall on the eastern side of the caldera. Columnar jointing is present in this very thick main Cone lava flow.
This image hightlights the advantage of spending more time on the island than any geoscientist before me. All of my predesessors were people who may have visited the island with a tour group and grabbed a sample of two, and then wrote up a short paragraph in a paper. By doing a bit of "bush bashing" I discovered two, never before visited but very significant outcrops, in the caldera wall. The next four images are at Location A, and the remainder are at Location B.
Location A - Interbedded with the main cone lavas was this beige-coloured ignimbrite sequence which showed a general fining upwards in each unit. The basal layer of each ignimbrite is a surge deposit. It was uniquely cemented, as no other ignimbrite unit on the island was this cemented. It is highly likely that this unit was altered and cemeted by hydrothermal fluids.
Location A - the ignimbrite unit shows the standard ignimbrite unit sequence with base surge deposits at the base grading up to a massive, fining upwards unit.
Location A - The base surge, lower unit of the ignimbrite. The surge deposit shows cross bedding, and it also contains abundant accretionary lapilli.
Location A - At the bottom of the ignimbrite sequence at this location, the beds of accretionary are in a cross-bedded unit which show that the accretionary lapilli were deposited by a surge cloud that was very wet. Thus the intial eruptive episode of this ignimbrite sequence possibly was affected by a previously, but now no longer existing, crater lake.
SECraterWall.jpg)
Location B - You wonder how with the multitude of visitors to Mayor Island, no one had ever been to this locality. Now it is famous for the overlying lava unit which has been written up in sevaral paper as being a unique flow which was a low-viscosity fountain-fed lava flow. Here the flow drapes over a previous escarpment as defined by the discordant lava flow - tephra unit contact. These two people were 1st other than myself to visit this locality and my supervisor now Professor Roger Briggs, being the one on the right, wrote one of the papers (Stevenson, Briggs and Hodder, 1993)
Here a major time break in the Mayor Island volcano was discovered. The red coloured unit is a poorly developed palaeosol (oxidised iron staining) which indicated a period of quiescence. Not only that, there was time for trees to grow.
My Major discovery and the 2nd ever date to be determined for the volcano. Here a largely intact tree trunk was discovered, lying on its side, and it is included within Plinian pumce deposit that was the initial phase of activity, after the quiescence, leading to the low-viscosity fountain-fed lava flow. The woody material was sampled and C14 dated - age determined as 8,000 ± 75 yrs B.P. Consequently, this date has proved to be very significant.
Close-up view of the tree trunk that was discovered at Location B. C14 dated at 8,000 ± 75 yrs B.P.
The spectacular view from Location B. View to the south, across Te Paritu Lake, up to Tutaretare trig (320m).
A beautiful bush walk. The track along the top of the caldera wall above the vicinity of Location A.
