Background to the archaeology of Ahuahu Great Mercury Island

Ahuahu Great Mercury Island is the largest island in the Mercury Group off the east coast of the Coromandel Peninsula. The northern half of the 1700 ha island is farmed in mixed sheep and beef grazing and the southern half of the island is planted in pine trees. It is very much an island of two halves joined by a relatively stable sand flat of low elevation.

The northern half of the island has andesite overlying older rhyolite, and the southern half is rhyolite, reflecting the volcanic activity which formed the island and the Coromandel Peninsula, and occurred at two separate times – in the Pleistocene -Pliocene period between about 2 - 5 million years ago, and the Pliocene - Miocene,  several million years earlier. The soils which form on the parent rocks are different, and one of our research questions is to investigate whether the distribution of sites, and types of sites, on the island are related to the geology and soils.

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The cultural landscape

The island has a dense and well-preserved cultural landscape. There are 23 pa defended by ditches and banks. In the northern part of the island there are also large areas of Māori gardens easily recognised by surface stones having been rearranged into lines down the slope, and cross walls which allow soil to be built up behind them to create deeper soils for gardening. There are also sites where basalt from Tahanga at Opito has been worked into adzes, sites with depressions in the ground where kumara were stored in underground rectangular pits, and some sites with shell midden. 

Tool-making

There is abundant chert, a fine grained volcanic stone which comes in several colours, which was flaked to make cutting and scraping tools, and petrified wood, also used to make tools. The Coromandel region has some of the most valuable stone resources in the North Island – basalt from Opito used to make adzes and obsidian from Cook’s Beach, Hahei, Mayor Island and Whangamata. All of these stone materials have been found in excavated sites on the island.

A shell-midden revealed

In 2009 a severe storm eroded about 10 metres of sand from White’s Beach in the centre of the island exposing shell midden and a charcoal-rich black layer about 1.5 metres down from the top of the dune. Samples of shell and charcoal were collected, and given a unique number in Archsite, the national database of archaeological sites (T10/944). Sea mammal bones, fish and dog bones were present in the sample and shell was radiocarbon dated to around the late 1400s. This site was investigated further in 2012.

The evidence for gardening

In the northern part of the island, surface rock has been moved around to create linear rows down slopes. In some sites the lines consist of single stones placed end on end, in other sites multiple stones have been piled up to form a row elevated above the ground surface. There are 21 areas of gardening, the largest is at Tamewhera in the northwest part of the island and covers several hectares.

Other less obvious garden areas consist of parallel drains running down a slope, which are now only visible at certain times of the day or seasonal conditions. Kumara storage pits were often left open when finished with, and these are now visible as roughly rectangular depressions in the ground. Kumara pits are present in a number of sites including pa. Two large pits excavated on Stingray Point Pa in 1955 must have held a large quantity of kumara.

Archaeologists on the island

Stingray Point Pa

In 1954 a party of archaeology students accompanied Jack Golson a recently appointed lecturer in archaeology at the University of Auckland to the island. After recording some sites they excavated a terrace on Stingray Point Pa (Matakawau) which had two kumara storage pits. Within each pit there were more than 80 postholes, most representing rebuilding of the roof structures but also later activities on the terrace dug into the infilled pits. There was a complex system of drains inside each pit to remove any water which seeped in and also larger features to drain the water outside the pits.

A more comprehensive site survey of the island in 1972-3 by Steve Edson, a student at the University of Auckland identified 91 sites, and provided maps of most of the pa.

Huruhi Harbour

Professor Geoff Irwin of the University of Auckland carried out an excavation of a pa in Huruhi Harbour in 1984. The pa was relatively small but was unusual in that the ditch and bank which provided the defensive barrier between the interior and exterior of the pa only covered half of the distance from one side of the pa to the other. Excavations showed there were no other means of defence such as palisades. Perhaps the ditch and bank was incomplete.