Of rocks and volcanoes - December 27th

We’ve had a few adventures that have involved rocks the last few days with the trip to the Summit and the sleep out on the Rangatira Trig.

So it must be time for me to delve into the geology of the Chathams. The cool thing about geology is that you get layers in rocks and if you drill deeply into them, or they happen to be exposed on a cliff face for example, you can read millions of years of history like you do a book. The modern rocks are at the top and the deeper you go the older the rocks. Well, you can do that if you’re an expert, which I most certainly am not!

Here however is what I do know:

The Chatham Islands are on the Pacific plate, which is the same plate as much of the South Island of New Zealand. The Chathams are also part of what used to be Gondwanaland. Gondwanaland was a great southern continent which over eons slowly split apart to form South America, Africa, India, Antarctica, Australia and New Zealand. The way that the experts know this is because of fossils which have been found here. Continents that used to be part of Gondwanaland have fossils of spores of mosses and fern and pollen from conifers (cone bearing) trees.

Rangatira itself is made up of sediments which accumulated from a volcanic vent which erupted about 4 million years ago. Often volcanoes erupt at the edge of continental plates, but here at the Chathams we are right in the middle of a plate so the volcano was probably what they call a “hot spot” which are areas beneath the earths crust that are so hot that they are able to puncture through a continental plate.

What I can tell you for certain is that there are enough flat rocks on Rangatira Trig so that you can fit four mattresses comfortably and no one is in danger of falling off!