by Chris Barrett
Christine, (my wife) and I have just returned from a 9-day trip to the North Island of New Zealand. We both love nature, and while there did our best to see as much of the area as possible.
We spent a week based in the beautiful, tourist-popular, coastal town of Piahia at the Bay of Isles.
On the way to Piahia we passed by Portland, a locality just south of the coastal city of Whangarei. Outside Portland is a large quarry. Its walls are a cement grey limestone. It is quarried for making cement, but also blocks and rocks for other uses are produced. The limestone is around 100 m thick, with all but the upper 13 m being consistently high grade limestone. All formed from ancient sea floors.
The quarry is quite deep, cutting down into the side of a hill, but even at its lowest point is 63 meters above sea level. There is also coal underneath some of these areas of limestone to the north and west of Whangarei. A mine just 1.5 kilometers (km) north of the quarry had produced in excess of 4 million tons of coal from beneath this limestone level when it finally closed in 1971.
Heading northwards, we found ourselves driving over a landscape built around and over volcanic rock. We passed hills formed by volcano peaks, long since worn down. Much of the flow from volcanoes was spewed on top of the limestone level, which in places was heavily eroded before being overlain with the volcanic flows, which are in turn heavily eroded. If you want a glimpse of how erosion has effected volcanic basalts just Google “wairere boulders northland” and search images.
Kawiti Glow Worms
Some 50 km of winding road later, we passed a sign to the Kawiti glow worm cave. The turn off was about 5 km south of Kawakawa, and only half an hour’s drive from our destination.
We returned to the Glow Worm Cave the next day. The cave is about 200 meters long and runs underneath a layer of limestone. Basically the creek takes a shortcut from one side of a limestone ridge to the other. This is the same layer of limestone as at Portland, 50 km to the south. Again, it is formed from uplifted sea floor. It is not continuous because of either erosion or burial by volcanic activity.
The valleys that form the ridge are caused by erosion. Massive boulders hang from the edge of the creek where the cave exits the ridge; signs that the creek exit was once hundreds of meters farther out, the ridge much wider, and the cave much longer.
Our Maori guide gave us a fascinating commentary as we followed his glow worm-like lamp along the walkway. The worms only inhabit the upper regions of the cave where climbing crickets and floods cannot reach them. They looked like a milky way snaking their way along the pitch of the cave roof. The glow of the worms is effective in attracting flying insects to their doom.
Apparently a 26-year-old Charles Darwin went through the cave on Boxing Day, 1835, when he spent 9 days at the Bay of Isles, Piahia region. Here is a link which provides a fascinating insight into this event: https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10620386
After exiting the far end of the cave we climbed back over the ridge to the entry via an amazing path winding through massive, eroded chunks of limestone. Some boulders were up to 10 meters high, and carved into all kinds of fascinating shapes by the elements. It was this limestone erosion that was leaching down into the cave below and forming massive stalactites. Some are meters in diameter.
Much of the North Island was home to the massive, long-lived Kauri trees. Sadly, 90% of New Zealand's forests were destroyed by logging, farming and fire. In the 10% that remains there are just a few dozens of the larger kauri's with a diameter over 2 meters left.
We visited the largest few. Te Matua Ngahere, (Father of the Forest) has a diameter over 5 meters, and Tane Mahuta (Lord of the Forest), is 50 meters high with a slightly smaller diameter than Te Matua. Both trees are estimated to be almost 2000 years old. Later, in the Museum at Te Papa, we saw age rings on slightly smaller trees and the rings are clearly discernible in the kauri timber. In the museum we also saw illustrations of the tree trunk sizes of massive Kauris seen and recorded in the forests before logging and fires destroyed them. The largest was the famed The Forest Ghost, which was reportedly measured at 8.54 meters diameter. Tragically The Ghost was consumed by fire in 1890.
Lost Forests of the Past
These Kauri trees are impressive, and standing at the base of a 2000-year-old tree is both humbling and sobering, but it does not stop there. Traveling further northwards, we stopped at the Gum Diggers Park. This is 130 km northwards as the crow flies. Over 100 years ago Kauri gum was a valuable commodity, its resin being used in paints and other products. The gum forms on limbs and injuries on the Kauri. It then either falls to the ground and is buried on the forest floor, or is buried when the tree falls. This gum is typical of many conifers, but is of a superior quality on the kauri. Over 10,000 tons of gum was exported from New Zealand, and the country earned more money from gum than gold, another of its early resources. The kauri gum has the same appearance and qualities as amber. Some has aged significantly and is of amber quality, some is less aged, and is still called “gum” even though it is very hard.
Early pioneers, assisted by the Maori people, discovered that the swamps in the northland of the North Island were host to large amounts of gum from buried kauri forests. Thousands of buried kauri trees lie under farmland and swamps in the region. For reasons unknown, every buried tree found is lying east to west. Some suggest a tsunami.
These trees have been buried quickly and are preserved in peat bogs and swamps at depths of over 2 meters. The Gum Diggers Park has exposed one of these massive logs for tourists to see. Excavated down to about 3 meters with a stairway and decking beside it in the pit, lies a massive kauri log. The log is from a tree of a size indicative to be over 1000 years old. Information on the site suggests the tree was buried over 40,000 years ago.
Standing in the pit, looking back up at the wall extending to the swamp floor, is a journey in time. The swamp floor is not the highest level the land had reached. Protruding down from the current surface are the lower sections of taproots from a massive kauri tree. If you can imagine cutting beneath the roots of a tree about a meter below the base and leaving the roots below that point intact, you may begin to picture the scene. Effectively, high up above the current swamp floor there was a giant kauri tree, now long gone, and the floor has since eroded away to its current level, leaving just the lower section of its massive root system.
The wall of the pit extends down almost 2 meters to the top of the log, and shows a myriad of layers of time. Forest layers, seasons, fires, decomposed trees, and measures of life are compressed down into dense layers of peat, clay and gum: Then there is the log itself, buried in almost 2 meters of more rapidly deposited material. But, that is not the end. We did not see it, but apparently beneath this massive log lies yet another level of forests, occupied by even older logs, buried in an earlier mass destruction of kauri trees. Data on site suggests this older forest reaches ages of 100,000 years and was also destroyed by a large event.
The land at Gum Diggers Park is only meters above sea level, but is apparently geologically similar to the limestone seen elsewhere.
After Gum Diggers Park we went to the very top of the North Island and stood at the tip overlooking the convergence of the Pacific and Tasman seas. Their currents seemed to clash in a long line of eddies and sandy turbulence, perhaps reminiscent of the forces that have shaped the land of the long white cloud.
This is a selective overview of a fantastic time in NZ, and there is much more I could tell. If you read my wife's diary of the holiday, you would get an entirely different picture. For me, the very breeze blowing through the canopy of towering forest trees spoke of an ancient past, and the musty, earthiness of peat bog logs smelled of deep time.
Of course, I did not get to see the extinct Moa. Nor did we get a chance to see the critically endangered Kakopo, the world’s largest, but flightless, parrot. I did see a stuffed Kiwi in the museum; better luck next time. I cannot see any of these in Australia.
I share these snapshots because they are relevant to the age of this earth and living things upon it. I have drawn no conclusions. Observant readers will quickly see there are significant pointers to geological layers, ages and sequences which may raise challenging questions in light of traditional creation and flood stories.
Below is a map of the geology of the area with locations mentioned above identified, also a legend to match. Source: https://www.otago.ac.nz/geology/research/general_geology/maps/nzgeolkey.html