The Bream Head Reserve contains iconic geographical features that dominate the eastern seaboard of Northland. The mountains support striking geological structures that are the basis for much northern Maori mythology and are recorded on maps and charts of the earliest European explorers.
The Heads lie at the southern end of the Whangarei Peninsular about 45km south east from Whangarei. The distinctive land forms are the eroded evidence of a group of volcanoes active in the early Miocene (24-21 million years ago).
The volcanic period itself lasted around 6 million years. The tectonic fault line is one of the fractures between the Indo-Australian plate and the Pacific plate.
While the fault line is active elsewhere, there has been no volcanic activity around this part of the Northland allochthon for a long time. The geological explanation is that a subduction-related volcanic belt became active to the west of the current land in Northland in Miocene times and gradually moved south down to Taranaki. It produced mainly andesitic stratovolcanoes. Most of these volcanoes have been eroded, but remnants form the Waipoua Plateau and Waitakere Ranges (andesitic, 22-16 Ma). An eastern volcanic belt formed mainly andesitic volcanoes around Karikari (22.3-19.8 Ma), Whangaroa (20.5-17.5 Ma), Whangarei Heads (21.5-16.1 Ma), Bream Head, and created the Hen and Chicken Islands (19.5-16.5 Ma).
Variety of Rock Types
As with most of New Zealand, the basement rocks of the region are mainly composed of greywacke (indurated sandstone), argillite, and chert, together with volcanic rocks, such as basalt pillow lava. The distinctive chimneys or pipes on Whangarei Heads, Manaia and Mt Aubrey are the heat-hardened, most durable remnants of narrow cones of solidified magma and are largely composed of kimberlite or lamproite.
The surrounding landscape is composed of the eroded materials from the volcanic activity. They are supplemented and overlaid with dense orange red clays typically visible in roadside cuttings and construction sites.
Natural erosion created the land forms we see today. Human interventions that have modified the landscape are also visible. The Heads contain archaeological evidence of human contact dating back 800 years – to the beginnings of settlement of Aotearoa. Prominent hills and ridges show evidence of villages and gardens with terraced and fortified retreats for defending themselves against invaders.