Northland is a narrow peninsula, stretching about 330 kilometres from Auckland to Cape Rēinga. Of this, 265 kilometres (including the Aupōuri Peninsula) is within Northland’s administrative boundaries.
The region is 85 kilometres across at its widest point, and 7.5 kilometres at its narrowest. The typical inland landscape is rolling hill country. Flat land is rare, and found mainly in narrow river valleys and coastal areas. The main upland areas are the Maungataniwha, Tūtāmoe and Waimā ranges, with the highest point around 780 metres above sea level. There are spectacular remnants of old volcanoes at various places, including Whangārei Heads and around Whangaroa Harbour.
Coastal and inland waters
The coastline, about 1,700 kilometres long, is the most distinctive feature. The straight western coastline is indented by several extensive, shallow harbours, the largest being Kaipara and Hokianga. The east coast has an irregular outline, with rocky headlands, deep-water harbours, and sheltered, sandy bays and beaches. Numerous islands lie off the east coast. The main groups are the Hen and Chickens, Poor Knights and Cavalli islands. The Bay of Islands is named for its sprinkling of 150 islands.
Rivers and streams dissect the land. Many are short, with small catchments. Intense rainfall causes flash floods, while prolonged summer dry spells reduce the flow in smaller rivers. There are several small, shallow lakes, of human construction or formed by dune or volcanic activity.
Northland has been shaped by geological processes for over 250 million years. The land has changed size and seas have advanced and retreated many times. About 25 million years ago there was widespread overthrusting of rocks from the north-east. Geologists liken this to a giant bulldozer scraping all before it and slowly rolling it over and over. This has produced a complex arrangement of sedimentary and volcanic rocks.
A different direction
The way Northland points to the north-west is believed by scientists to be a remnant of New Zealand’s original geological orientation. This angle was established between 60 and 80 million years ago, when the opening of the Tasman Sea separated the New Zealand micro-continent from Australia and Antarctica. The rest of the country has been bent around to a north-easterly axis during the past 30 or so million years.
The foundation rock is mostly greywacke, a hard compressed sandstone that was laid down on the seabed between 280 and 135 million years ago. This was once covered by layers of softer rocks – sandstone, coal deposits, limestone and shale – that have eroded away.
Uplifted blocks of greywacke form the broken hill country between the Mangawhai and Whangaroa harbours, and to the west of Whangārei. Deposits are progressively deeper further west, and are over 5 kilometres below the surface along the coast near Dargaville.
Ancient volcanic rocks make up many of Northland’s ranges. In more recent times the inland Bay of Islands became peppered with volcanoes, some of them active until 2,000 years ago. From Matauri Bay south to Tāheke and eastward from Hōreke to Paihia, there were over 20 centres of eruption. Lakes, swamps and waterfalls formed in and around lava flows.
The soils were the despair of early farmers. Most are strongly leached, warm, heavy clays with thin topsoils and low subsoil fertility. Although much of the forest has been removed, its influence on soil formation was marked. Kauri trees produced deep layers of highly acidic litter, resulting in poor soil. Although drainage and fertilisers can improve productivity, many of the soils are better suited to forestry than to agriculture.