Paku on the Coromandel

Paku at the Mouth of Tairua Harbour.

The story of Paku involves an eight million year building project. It started with two crustal plates grinding relentlessly past each other.

• Chapter one opens eight million years ago, with an explosive eruption that blew pumice and ash from a fissure, leaving a vent surrounded by ignimbrite and breccia.

• Chapter two begins with rhyolite lava squeezing through the fissure into the surrounding ignimbrite, building a rhyolite dome.

• Two massive crustal plates locked in an eight million year slow-motion collision generate large quantities of energy. In chapter three of Paku history, a violent eruption cleared the vent and rhyolite lava was free to flow over existing structures. A new dome forms, crowning the original. Towards the end of the chapter, the sticky lava mess cools and solidifies. Eventually, the lava in the fissure solidifies, plugging the vent ending a violent period of history.

• Chapter four tells the story of global warming. It lasts 20,000 years, taking us to the present day.

• Chapter five begins with another round of global warming. The ending lies in an uncertain future as we attempt to halt its progress.

Tairua, two tides.

Nearing the end of the last ice age, about 20,000 years ago, Tairua was a broad river valley far from the coast.

Global warming released an immense volume of water from the polar ice caps, while sea levels rose as much as 120 metres.

Sea levels rose at a rate of 10 metres every century and reached their current peak about 6,500 years ago.

Vanishing Volcanoes.

Every rock has a story; every landscape has a history.

The geological history of the last 4.5 billion years is a work of fiction based on fact. The curved fluid writing of rhyolite punctuated with breccia and ignimbrite tells the history of Paku.

A dome within a dome

Twin rhyolite domes shared the same vent. Eight million years of exposure to sun, wind, rain and tides have reduced large parts of the original structure to volcanic rubble.

Cold hard facts, the rocks.

Molten rhyolite (darker colour) pushed up the vent into the overlying light coloured ignimbrite.

Darker material is rhyolite; the rest is ignimbrite at the base of Paku.

Molten rhyolite has the consistency of thick treacle.

The glass used in windows and drinking glasses is almost entirely silicon dioxide (SiO2)

Rhyolite has a very large silica content. It isn’t surprising it is highly viscous like molten glass and flows like thick treacle.

Rhyolite, a swirly ropy messy treacle lava flow.

Bands in rhyolite lava

Rhyolite is easily recognised by layers or bands. The flow banding pattern results when quart and feldspar minerals segregate during slow cooling as the lava flows.

Bands close together can indicate the lava was flowing faster.

New Zealand's Coastline in the Ice Age.