Why are Caribbean tides so small?

19 April 2016



Why are Caribbean tides so small?


Kat Arney put this to Chris Smith...

Chris - Okay. The likely reason for this is the same reason you don't see very high tides in other parts of the earth's surface, and that is it's all down to how the water moves.

The reason water moves around the earth is because the earth is spinning inside the orbit of the moon, the moon is gravitationally attracting the bulge of water towards itself on the side of the earth closest to the moon, and there's also another bulge on the opposite side of the earth.

The earth then turns through that bulge, which effectively moves across the surface of the earth and it's going to interact with land masses. So if you have a certain coastal configuration that means that the water all heaps up in one place because it's got nowhere to go, you're going to see a bigger tide there than if the water can distribute and flatten out easily. 

A really good example of this is the Severn Estuary in the Bristol Channel. You've got the patch of the coastline of Wales and the north of Devon and Cornwall which narrows in like a funnel to a very narrow patch of coast. All of the incoming tide gets funnelled into a very small part of the estuary which heaps up the water there, drives a lot of water inland very fast and then it comes out again, and that's you get these very big tides.

In some places, when I was in Australia last year, I went to somewhere where some of the highest tropical tides are, in Northwestern Australia, up where the horizontal falls are, and it's between 10 and 13 metres the tide there.

So that's the reason - it's because the water having little place to go and being funnelled from a massive ocean into a relatively narrow section of the earth's surface and, if you have a lot of water entering a small area, you're going to get a very radical tide height change.


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