Distribution of Mid-Ocean Ridges in the Southern Hemisphere

It is well known that land mass around equator is regularly distributed. The three mid-ocean ridges of the Pacific, Atlantic and Indian oceans are found to be aligned 90° apart, directly N-S, reaching southwards from equator a couple of thousand kilometers. Studying the N-S aligned volcanic zone of Northern Iceland, it is interesting to see that it is found directly north of the Mid-Atlantic Ridge of the Southern Hemisphere. The pattern of those three N-S aligned ridges therefore form an interesting pattern with Iceland included, far up north!

The drawing is superimposed on [Manuscript painting of Heezen-Tharp “World ocean floor” map by Berann]. https://www.loc.gov/item/2010586277/

How can these ridges be so regularly distributed, besides being found in context with the volcanic zones of Iceland? The answer is found in the convection rolls pattern formed by different layers withing the mantle. Together they form N-S oriented polygons, and the crust breaks in harmony with the resulting pattern. In many cases, though, ridges follow the division lines between convection rolls, and in some cases they follow other mathematical rules as well.

The fact, that the intervals between the parallel N-S sections span 90°, further adds to the feel of regularity. Each interval corresponds to the width of three convection rolls, each spanning 30° from east to west. To fully understand this, the whole system must be kept in mind, but this is a good beginning to consider what is going on.

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