Many of us live in countries where we tend to take the natural world and nature for granted. We know that there are trees, animals, hills and rivers but we tend to just assume that they will always be there. This week that we have spent in and around Rotorua in New Zealand has made me realise how very different nature can be and how volatile, or uncertain, everything really is. As you may know our earth is made up of three separate parts the core, the mantle, made up of hot rocks and gases, and the crust. The core, like the core of an apple, is in the middle. The crust, like the crust on a slice of bread, is on the outside, which leaves the mantle in between these two. The core is solid which is why, when I was very young I could never dig down to Australia like I thought I could. Actually I always got bored after about half a metre so that may be another reason.

The mantle is a layer of hot melted rock that covers the core and the crust, which is the thinnest layer, sits neatly on the mantle. However it is still in most places about 80kms thick. What is more the crust is divided into 14 major tectonic plates. Some people say less, some say more but you and I don't really care how many just that there are some and they are there. Unfortunately these crusts are moving, very slowly but they are moving. That means of course that the earth hasn't always looked how it is today. Once all continents were probably linked together in a big landmass called Pangaea. Then this split into two and then bits started dropping off these two until we are where we are now. But we are still moving. New Zealand is heading north at the rate of about 1 centimetre every three years. But if you're planning to go to the equator don't sit at Cape Reinga and wait because you may be a bit old when you get there.

It is the crusts or plates that are moving. There are three types of crust; oceanic, continental or a bit of both. Oceanic crust is much harder. The crust can either move together or apart. When moving apart, new crust can form in the gap but in New Zealand that is not what is happening. New Zealand sits directly on the border between the Pacific Continental Plate and the Indo-Australian Plate and they are moving together. In the North Island the Pacific Plate is pushing under the Australian one while in the South Island it is the other way around. So what, you may ask happens when they do this and I will try and tell you. In simple terms you get earthquakes, volcanoes and mountains and New Zealand has loads of these. Plates pushing against each other cause stress, think about standing in a queue of people and think of the stress there, and when the stress gets too much the plates jump apart causing an earthquake. When a plate dives below another one its rocks go down into the hot mantle of the earth and then can be forced back, especially if the crust or plate is quite thin above it, in the form of a volcano. The rock is often thrown into the air but if this happens underwater it rapidly cools and forms new rock creating islands.

In and around Rotorua the actual crust of the earth is very thin so the hot rocks and gases are really near to the surface. When you arrive in Rotorua it looks as though everyone has got their kettles boiling because steam seems to be rising everywhere. All around the town, on the banks of the rivers and up into some of the hills you can see steam, all day, every day. But that is not all. In some places the steam actually gushes up into the air at regular or irregular intervals. These gushes are called geysers and they happen because the pressure of the hot water below has found an opening of soft rock and the steam can, every so often, escape. In other places you can actually see the water in pools bubbling and when we were at a place called Whakarewarewa we watched one pool and after about ten minutes the water suddenly rose up about 20 cms, stayed like that for a minute or two and then went down. We were told this happens every hour.

In some cases the pressure under the ground will force a layer of mud to spurt forth. Now all of these gases that are bubbling away contain minerals and elements which, when they reach the surface and react with air or water leave deposits on the surface. In many places around here you can see multi-coloured rocks. These gases are also what give Rotorua its very distinctive smell. The main gas that causes this is sulphur and it smells a lot like rotten eggs. After a while, so the residents say, you tend to get used to it. But talking of residents brings me to another point. Nowadays everyone knows what is going on here. Scientists can explain it although they know they cannot completely predict what is going to happen and when. All of the attractions where you can walk among these bubbling pools, geysers and hot rocks are checked every day to make sure they are safe. Quite often the crust can be so soft that it will just collapse and a big crater will form.

So what must it have been like for the very first Maori who came here? How did they know which bits to walk on, where to build their villages and what would collapse next. I think we learned from Whakarewarewa village, which has been there among the hot pools and springs for over 160 years that, the Maori watch nature very carefully and, through experience, observation and traditional knowledge they can see and understand things really well. Of course how many Maori were hurt or even killed in those first few years we don't really know but it must have been quite strange to them. Thinking about it, the whole idea of living there seems quite strange to me today. When the pool at Whakarewarewa begins to rise you can feel the earth tremble beneath your feet; when you walk in some places you can put your hand on the ground and the earth is really hot; when you think that there is a geyser maybe waiting to push through the earth right below your feet then you really know you are living among nature. It's quite amazing and I hope the pictures show something of that feeling to you.