Northland is a narrow peninsula, about 330 kilometres long from Auckland to Cape Rēinga. Of this, 265 kilometres (including the Aupōuri Peninsula) lie within Northland’s regional and 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, found mainly in narrow river valleys and coastal areas. The main upland areas are the Maungataniwha, Tūtāmoe and Waimā ranges, peaking at around 780 metres above sea level. There are spectacular remnants of old volcanoes at various places, including Whāngārei 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 with several extensive, shallow harbours. The largest are those of 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 coast. The main groups are the Hen and Chickens, Poor Knights and Cavalli islands, and 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 dry spells stem the flow in smaller rivers. There are several small, shallow lakes, man-made 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 moved the New Zealand micro-continent away from Australia and Antarctica. However, except for the southern South Island, the rest of the country has been bent around to a north-easterly direction 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 135 and 280 million years ago. This was once covered by layers of softer rocks – sandstone, coal deposits, limestone and shale – that eroded away.
Uplifted blocks of greywacke form the broken hill country between the Mangawhai and Whangaroa harbours, and to the west of Whāngārei. 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 up to 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 was 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 agriculture.