Monday, August 16, 2010
Everyone is familiar with the term "sea level." We all know what it means. Or do we?
Of course sailors know that the sea isn't really level. There are waves and tides and wind surges and storm runoffs and all sorts of other factors that affect the level of the sea. So we use "mean sea level", the average height of the ocean, often measured as the halfway point between the mean high tide and the mean low tide. Then we can measure tides and surges in relation to mean sea level, usually only a few feet up and down.
So mean sea level is.... ummm level. The same height all over the earth. Right?
Well, not exactly. It all depends on what you mean by "height". The variation in the distance of the mean sea level of the ocean as measured from the center of the earth varies by many miles from place to place. Yes... miles.
It's all because of the earth's rotation. The earth isn't a perfect sphere. It's an oblate spheroid. It bulges at the equator. You knew that, right?
The land bulges. The sea bulges. So what if we could magically make the seas and oceans really level? For example, what would happen if the earth stopped spinning one day? No more centrifugal force. No more bulging. Over time, the earth’s shape would approximate a perfect sphere, but the most immediate readjusting would be done by the oceans which currently bulge as much as 5 miles at the equator.
The picture at the top of this post (shamelessly stolen from Strange Maps) shows what the map of the earth's continents and oceans would look like if the earth stood still and the seas leveled themselves out. Goodbye Canada, Russia and Europe. Hello to an equatorial megacontinent ringing the globe and two polar oceans.
You could drive around the world on land. I guess some record breaking circumnavigators would eventually bike it, walk it or run it. Leaving aside the issue of what wind patterns there might be on a non-rotating earth, you couldn't do a sailing circumnavigation any more, at least not in the sense of a route that crosses the equator and crosses every meridian. The best you could do would be to sail a circuit of the Southern Ocean or a similar route crossing every meridian in the new Northern Ocean at the latitude of the USA/Canadian border.
How strange is that possum?