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Iceland isn't only situated on a divergent boundary (which in itself can rise up to shallow depths because of higher static and dynamic lift btw.) but also on a (postulated) pretty deep rooted mantle plume that may produce enough magma to rise to subaerial heights. Edit: The magma that erupts at an ocean ridge is "welded" to the sides ("sheeted dykes"). ...


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The reason islands don't form along divergent plate boundaries is that these boundaries are at the bottom of the sea, and usually quite deep. Although mid ocean ridges are volcanic, the magma doesn't get a chance to pile up and reach the surface because the plates are not static. They are slowly spreading apart, and the magma is needed to form fresh oceanic ...


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