Intertidal 2015

description / images

This project explores environmental changes over the last 800 years on a small stretch of Northland coastline, the sandspit at the mouth of the Mangawhai Estuary.

Paleoenvironmental evidence suggests that the dunefield at Mangawhai was once forested with totara, hoheria, titoki and matai. This coastal vegetation was destroyed by fire around 800 years ago. Subsequent incursions of wind-blown sand from the beach and foredunes have resulted in a layer of charcoal being trapped beneath metres of sand. Easterly gales periodically expose edges of this seam and blast particles into the air where they blend with sand. Then, according to density, size of grains and the variability of wind speed and terrain, everything comes to rest in extraordinary patterns – swirling arabesques, subtle and infinitely complex.

Mangawhai exposed carbon Bruce Foster NZ

There are 16 middens on the site, many extensive in area and up to a meter in depth. After centuries of erosion they now sit on sandy pedestals and mounds, some around 13 m high. They contain the remains of a variety of fish and shellfish species, including snapper, jack and blue mackerel, and closer to the surface, pipi and tuatua. These refuse heaps are evidence of 150 years of kaimoana harvesting which began about 450 years ago.

Mangawhai middens 0766 Bruce Foster NZ.jpg

Scattered across the surfaces of many middens are the fractured remains of oven stones. These volcanic rocks probably have their origins 5–12 million years ago, their stories revealed now in their textures and fractures and gradations of colour. Some have been smoothed by persistent sand blasting, others look as though they’ve only just come out of a fire – sharp and angular and tinged with wood smoke.

Mangawhai fractured umu stone Bruce Foster NZ

The last person to hold one of these stones was cooking shellfish here around 1600. They were quite possibly Te Uri ō Hau or Ngāti Manuhuri people. Their occupancy came to an abrupt end with the battle of Te Ika ā Ranganui in 1825 in which the local people were decimated. The invading Ngāpuhi then scoured the district for survivors who were killed and buried on the coastline between Mangawhai and Pākiri. A tapu has only recently been lifted.

Mangawhai Fairy Tern refuge Bruce Foster

Since my first visit to the dunes in 1977, artefacts of the industrial age have washed ashore at Mangawhai in increasing numbers. Storm surges carry this material beyond the foredunes and gales distribute the lighter objects over the dunes. Degradation rates for these objects vary from up to 20 years for plastic bags, 450 years for plastic bottles and 600 years for fishing lines. As it is folded back into nature, this litter of unknown origin mixes, blends and sometimes mimics the debris of earlier human activity. The spit is also home to New Zealand's most critically threatened endemic bird,  the tara iti or fairy tern, a victim of introduced predators. This vast archeological site is an eerie place, a stark picture of dramatic and irreversible environmental change.

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Mangawhai Sandspit Excavation, 1978, Peter Pearce
Recent Evolution of the Mangawhai Spit Dunefield, 1988, N.J.Enright and M.J.Anderson
Submissions by the Auckland Regional Council, 2009, Vanessa Turner