Mountains and ranges
The Waikato region consists of valleys and coastal lands separated by ranges. The Thames valley is divided from the Waikato basin by greywacke hills running north through the Hapūakohe and Hūnua ranges. Another greywacke range separates the Waikato basin from the west coast. The Hakarimata and Taupiri ranges create a boundary between the middle and lower reaches of the Waikato River.
Waikato’s eastern boundary is the Kaimai Range, which runs south from Te Aroha, separating the Thames valley from the Bay of Plenty. The northern part is an extension of the volcanic rocks of the Coromandel Peninsula. The southern section consists of ignimbrite, which also forms the plateau at Mamaku in south Waikato. It was produced in volcanic eruptions in the Taupō Volcanic Zone 300,000–750,000 years ago.
A number of old eroded volcanoes ring the middle Waikato basin. To the west are Karioi, Pirongia and Kakepuku. To the east are Maungatautari, Maungakawa and Te Tāpui.
The Waikato River has changed course many times over several million years. Until about 20,000 years ago it flowed north through what is called the Hinuera gap at Piarere, down the Hauraki Plains to the Firth of Thames. Gradually, waterborne volcanic debris built up, causing the river path to turn sharply to the west near Maungatautari.
Rivers in the Waikato region are alluvial, which means they flow through flood plains they have created by depositing sediment. The largest, the Waikato, begins on Mt Ruapehu, flowing from Lake Taupō across the Volcanic Plateau, into the Waikato basin and out to the Tasman Sea. Its major tributary, the Waipā River, rises in the Rangitoto Range in the King Country. The two rivers converge at Ngāruawāhia.
The Thames valley is drained by the Waihou River, which flows from the Mamaku and Pātetere plateaus; the Piako River, which rises near Maungakawa; and the Waitoa River, which has its source in hill country near Piarere.
Wetlands, peat lakes and peat bogs abound in the Waikato lowlands, particularly in the central Thames valley, north of Taupiri and south of Hamilton. Drainage works to create farmland have destroyed some wetlands and split others into fragments. However, in the early 2000s the Waikato region still contained around 30% of New Zealand’s wetlands, including the Whangamarino Wetland and Kopuatai Peat Dome.
Harbours and coast
On the west coast are large tidal estuaries; the Raglan Harbour (Whāingaroa) and the Aotea Harbour. The coast’s distinctive ironsands have been mined at various places, including at Waikato Heads, for use in steel making.
There are small geothermal areas throughout the region. Although secondary to the large geothermal systems of the Taupō Volcanic Zone, some – notably the hot springs at Te Aroha, Ōkoroire and Waingaro – have been developed into tourist attractions.
The now-fertile loam soils of the Waikato basin were originally fine volcanic ash and debris that weathered. The Thames valley has poorly drained gley soils, made of alluvial material. The lower Thames valley and parts of the Waikato basin have peat soils, formed from decomposed wetland plants. Many of these gley and peat soils have been drained for agricultural purposes. The soils of south Waikato are derived from pumice – volcanic rock – and lack some important nutrients.
Fog and fire
Some say the notorious Waikato fogs were much worse when peat fires were common – as recently as the 1970s. Farmers clearing swampy land burned scrub, and the fire would often spread down roots to the peat below. As well as adding smoke to the foggy atmosphere, the long-burning fires had a distinctive smell and made a reddish glow on the horizon at night.
Waikato summers are long, hot and often humid. There is relatively high rainfall all year round, but in the early 2000s this pattern was disrupted. A severe drought in the summer of 2007–8 transformed the usually vivid green landscape to dusty brown, and further droughts were predicted.
Fogs often occur in winter, but usually lift to reveal a clear sunny day. They are becoming less frequent as a consequence of wetland drainage. Heavy frosts are also common in calm, clear conditions. Maximum daily temperatures range from 21 to 26°C in summer and 10 to 14°C in winter.