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Understanding Northern NZ

Book Review [1]
Out of the Ocean, Into the Fire: History in the rocks, fossils and landforms of Auckland, Northland and Coromandel.
by Bruce W. Hayward (Geoscience Society of New Zealand, 336 pages, distributed by Potton & Burton [2], $50)
Reviewed by Simon Nathan

outoftheocean-web22017 is the fiftieth anniversary of the development of the concept of plate tectonics – now widely accepted as an explanation of how the earth works, including the relationship between mountains, earthquakes and volcanoes. New Zealand is situated on a major plate boundary, and our understanding of local geology has been completely rethought in recent years.

This magnificently illustrated book is a synthesis of current knowledge of the geology and landscapes of northern New Zealand, a complex region that was difficult to understand before the era of plate tectonics. Although written for the non-specialist reader, the book is the product of decades of research, mainly by former students and staff of the University of Auckland, in which Bruce Hayward has played a prominent part.

After an introductory chapter, the text is organised into 11 chapters, starting with the oldest greywacke basement rocks, and progressively working upwards to the development of the present landscape over the last one million years. The text is interspersed with text boxes, which deal mainly with specific geological features, especially fossils, rocks and mining. The ‘Fire’ aspect of the title is covered in three chapters (6, 7 & 9) dealing with volcanism that has been semi-continuous over the last 24 million years, leaving many distinctive landforms. It is claimed that the volcanic activity is of greater diversity than in any other area of similar size elsewhere in the world – volcanic arcs of andesite volcanoes, giant caldera volcanoes, searing ignimbrite flows and rhyolite domes followed by over 200 small basalt volcanoes.

The region north of Auckland has long been puzzling to those of us from further south. Because of the warm climate the rocks are often deeply weathered, poorly exposed and prone to landsliding. There are many examples where the rock sequence appears muddled or upside-down. Recognition of the Northland Allochthon – a pile of huge landslide slices emplaced during the Miocene period – now provides an explanation, but the story seemed impossibly complicated to those without detailed technical knowledge. Chapter 4, “Northland’s displaced rocks” provides a masterly explanation of this major feature of Northland geology, well illustrated by diagrams and photographs. Incidentally, one of the keys to unravelling this confusing story has been the dating of different rock masses by microscopic fossils, a field in which Hayward has played a leading part.

The final chapter (13) is a guide to specific geological features of interest throughout the region, with maps and information how to find the localities.

One of the features of the book is the wonderful colour illustrations – photographs, diagrams and maps – typically with two to five on each full-page spread. I suspect that many readers will start by scanning the images, and then return to read the text in the sections that interest them.

This is a book written with great affection by an author who has spent much of his working life deciphering the geology of northern New Zealand as well as leading innumerable field trips to features of interest. His pride in the region is clear, with claims that it includes the largest cone volcano in New Zealand (Waitakere), the largest shield volcano (Waipoua), the whitest pottery clay as well as concretions that are much larger than the Moeraki boulders. In 2017 it is the definitive story of the geology and landscape of northern New Zealand – a wonderful Christmas present for anyone interested in the natural environment.

 

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