Auckland straddles the Auckland Volcanic Field, which has produced approximately 50 volcanoes. These take the form of cones, lakes, lagoons, islands and depressions, and several have produced extensive lava flows. Most of the cones have been partly or completely quarried away. The individual volcanoes are all considered extinct, although the volcanic field itself is merely dormant.

Unlike the explosive subduction-driven volcanism in the central North Island, such as at Mount Ruapehu and Lake Taupo, Auckland's volcanoes are fueled entirely by basaltic magma. The most recent and by far the largest volcano, Rangitoto Island, was formed within the last 1000 years, and its eruptions destroyed the Māori settlements on neighbouring Motutapu Island some 700 years ago.

Rangitoto's size, its symmetry, its position guarding the entrance to Waitemata Harbour and its visibility from many parts of the Auckland region make it Auckland's most iconic natural feature. Few birds and insects inhabit the island because of the rich acidic soil and the type of flora growing out of the rocky soil.

Harbours and Gulf

Auckland lies on and around an isthmus, less than two kilometres wide at its narrowest point, between Mangere Inlet and the Tamaki River. There are two harbours in the Auckland urban area surrounding this isthmus: Waitemata Harbour to the north, which opens east to the Hauraki Gulf, and Manukau Harbour to the south, which opens west to the Tasman Sea.

Bridges span parts of both harbours, notably the Auckland Harbour Bridge crossing the Waitemata Harbour west of the Auckland Central Business District (CBD). The Mangere Bridge and the Upper Harbour Bridge span the upper reaches of the Manukau and Waitemata Harbours, respectively. In earlier times, portage paths crossed the narrowest sections of the isthmus.

Several islands of the Hauraki Gulf are administered as part of Auckland City, though they are not officially part of the Auckland metropolitan area. Parts of Waiheke Island effectively function as Auckland suburbs, while various smaller islands near Auckland are mostly zoned 'recreational open space' or are nature sanctuaries.

Climate

Auckland has a warm-temperate climate, with warm, humid summers and mild, damp winters. It is the warmest main centre of New Zealand and is also one of the sunniest, with an average of 2060 sunshine hours per annum. The average daily maximum temperature is 23.7 °C in February, and 14.5 °C in July. The absolute maximum recorded temperature is 32.4 °C, while the absolute minimum is -2.5. High levels of rainfall occur almost year-round with an average of 1240 mm per year spread over 137 'rain days'.

Climatic conditions vary in different parts of the city owing to geography such as hills, land cover and distance from the sea, hence unofficial temperature records exist, such as a maximum of 34°C in west Auckland. On 27 July 1939 Auckland received its only recorded snowfall.

The early morning calm on the isthmus during settled weather, before the sea breeze rises, was described as early as 1853: "In all seasons, the beauty of the day is in the early morning. At that time, generally, a solemn stillness holds, and a perfect calm prevails..." Many Aucklanders used this time of day to walk and run in parks.

As car ownership rates are very high and emissions controls relatively weak, Auckland suffers from some air pollution, especially in regards to fine particles emissions. There are also occasional breaches of guideline levels of carbon monoxide. While maritime winds normally disperse the pollution relatively quickly it can sometimes become visible as smog, especially on calm winter days.