The Firth of Thames

The Firth of Thames is the large body of water that occupies a rift valley or graben between the Coromandel Peninsula and Hunua Ranges, and which continues into the Hauraki Plains to the south. The term firth is an old Scottish/English term indicating where a large river body empties to the sea, and the Firth of Thames is where the Waihou and Piako meet the ocean.

​

The Waihou River was named the Thames River by Captain Cook when he navigated almost 25km upriver in 1769, and the town of Thames grew at its southern point. The Hauraki Plains and the Firth of Thames history stretches back to prehistoric times, with the plains being formed by the original Waikato River which for over 300,000 years drained into the Firth of Thames.

​

Archiologists believe the catastrophic Oruanui eruption of the Taupo volcano around 26,500 years ago, estimated to be 15 times bigger than the better-known Taupo eruption around 1800 years ago, changed the course of the river at what is called the Hinuera Gap (south of Matamata). At this time the river found a basin south of the Manukau harbour and filled it, becoming the river we know as NZ’s largest today. 

Riverstones found in the cliffs alongside the Firth (as in Orere Point) trace their origins to those different geological times.