29th Feb

A very lazy day.

Popped over to the island for a look around. 30 minutes later we were waiting on the dock for the tender to come back.

The 'shops' go about 100m either side of the wharf, and that's about all she wrote.

Sarah wanted to look at the pearl shops, but the one onboard seems better.

Geography 101

Back to the reef quandary. I went to a talk about the types of islands. Now I understand. First, you will see on any map of this area, that the islands are in strings, going up and to the left. Up, and to the left. This is because... No. Let's go back a step.

Islands are volcanic. They are created when lava pours from a hotspot way under the sea floor, and makes it's way to the seabed. Like any volcano, it forms a cone, as it gets bigger. More and more lava comes out, the bigger the cone. Some are big enough to appear above sea level. Some? Not so much.

Now, back to the strings. The entire area is on a tectonic plate, which is moving. You guessed it, up and to the left. Northwest. Apparently it moves at about the speed your fingernails grow.

The tectonic plate is above the source of the lava, so that as the plate moves northwest, it leaves a trail of islands behind it.

If you have ever seen those guys making mini donuts at the mall, you will know what I mean. The dough blob is a predefined amount, which is squirted into the hot oil. The shape is set, and the new donut floats off, while another one is made in its place. That's the islands, a series of donuts floating along in a row. The islands in each string that are the oldest, are the ones at the top left of each string. The first donuts off the rank.

Now, because of the water temperature, as well as the alignment of other chemical planets, coral grows on the shores of these islands. Coral needs something solid to grow on, and it likes to grow towards the sun, so the shore is the perfect place. This is called a fringe reef.

Over time, the island itself starts to erode. Solid rock from lava will stay longer, but much of the other flotsam that makes up the land will erode more quickly. After a couple of million years, the shore line will have receded from the reef, sometimes a long way. The reef hasn’t moved, but the island is much smaller now, and there is a lagoon between the island and the reef. It is now a barrier reef.

Another couple of million years later, and the island may have disappeared altogether, leaving just the reef. It is now an atoll.

Look at that map of the pacific again, and the older islands to the north west, are either atolls, or they have barrier reefs and lagoons. The ones towards the bottom right are younger, and have no decent lagoons, and sometimes only fringe reefs. The aging process of an island chain is laid out in front of your eyes. Cool huh?