New Zealand was the last country to have been discovered, but was also the last to be formed. About 85 million years ago it broke away from Godwana, the super-continent that also contained Australia, Africa and India, and slowly it started to sink. It started out about half the size of Australia, but by the time it had finished sinking (about 35 m years ago) it was down to less than a third of the size it is today, and was mainly made up of islands. In fact, it’s first appearance was as an arc of volcanoes. Ash from volcanoes began to build up on the ocean floor, along with other marine sediment, limestone and coal, and a bigger continent started to form.
About 25m years ago a shift in plate movement began to split apart the still mainly submerged continent. This is why, today, New Zealand is made up of two islands, and also why it is split between two different massive plates, the Australian plate and the Pacific plate. The North Island is on the Australian plate but the South Island has the fault line between the Australian and Pacific plate running diagonally across it. Everything west of the fault line is on the Australian plate and everything east – including Christchurch where we are at the moment – is on the Pacific plate. These constantly shifting plates are the major cause of New Zealand’s earthquakes, volcano formation and activity. Also all the mountains and natural disasters and differences in geology are all due to how the plates are moving and sliding over each other. In fact, New Zealand is being squashed, stretched, rotated and twisted all the time.
So, a bit more about those plates. Apart from the Australian / Pacific plates pushing against each other (the two New Zealand islands move away from each other at about 50mm a year), the oceanic plates (thinner), and continental plates (thicker) are constantly colliding, and the oceanic plates and being pushed under the continental plates. This process is called subduction. You would think that the plates slide smoothly, but friction makes them drag, causing shifts and crumples that then cause shallow earthquakes. When the constant pushing means something eventually gives, that’s when you get a bigger earthquake. Also, the subduction causes melting of the earth’s mantle (the layer under the earth’s crust), which produces a volcanic arc, and the formation of volcanoes.
So, what does this mean for New Zealand? It has about 50-80 earthquakes a day (20,000 a year, with about 250 big enough to be felt). These occur mainly in the South Island. Since records began in 1848, 26 earthquakes with magnitudes of over 6.0 have been recorded. Christchurch’s earthquake of 2011 was the second biggest natural disaster for the country (after the 8.2 magnitude earthquake in Wairarapa in 1855), and killed 185 people. Even now, in 2015, the city is still struggling with how to repair major damage. The North Island is volcano-land, with about 70 of them, but many of these are dormant or extinct. There have been 8 significant eruptions since the Maoris settled in 1300.
New Zealand is part of the Pacific Ring of Fire as you can see in this picture. It’s a very beautiful country, but considering all the natural disasters, I would not exactly want to live here! The picture below shows the ruins of Christchurch’s once lovely cathedral. Most of the center of Christchurch is still like this as, after the earthquake happened 3 years ago, they discovered they are right on a fault line. Now. no-one wants to rebuild in the same places. It’s really sad – like the heartbeat of the city has been ripped out.