It's hard to imagine but Banks Peninsula was once an Island that stood for 12 million years separated by 50km of sea from the closest landmass.
Banks Island had a very large volcanic mountain on it that was covered in snow most of the year (when it was not live).
Some 20,000 years ago, the mainland joined with the island because of enormous erosion from the Southern Alps. Rocks and pebbles rolled down gullies or were washed along in glaciers, rivers and streams to create the fertile Canterbury Plains and the Peninsula.
Many ancient lava flows can be observed from our vessels including Cathedral Cave near Akaroa which is the best example on the Peninsula of lava flows and erosion by the sea.
The two harbours of Akaroa and Lyttelton are actually the twin craters of the magnificent volcano. About 2 million years separated the eruptions of Lyttelton and Akaroa. Ash and dust from these eruptions would have entered the atmosphere, reducing the intensity of incoming sunlight. The resulting effect on the climate would have enhanced the conditions that favoured growing glacial ice sheets during the Ice Age.
Around 11 million years ago the sea rushed in to create the much more peaceful environment that you'll experience today.
Volcanoes are not the most solid of structures and are essentially piles of cinders. Erosion quickly eats into the softer material, and even the stronger rock cannot survive once it is left exposed. Once activity ceases the volcano begins to crumble away. An extinct volcano weathers away at the same rate it grew in the first place. This is extremely slow in human terms but is very rapid on the geological time scale.
The Akaroa volcano was similar in height to Mount Ruapehu, which is an active volcano located in the centre of New Zealand's North Island.
