Evidence of crustal drift from Icelandic geology

Abstract

Iceland, the only substantial landmass astride a mid-oceanic ridge, supplies details of how the necessary dilation for continental drift could be accomplished. Two types of approach have been made. In one, the visible dilation—evidenced by gaping cracks and volcanic fissure eruptions—in the active volcanic zones crossing Iceland has been measured. It amounts to about 30 m in the last 3000 to 5000 yr. In the other, the dykes—dilation fissures infilled with once-fluid basalt— which fed the Tertiary lavas of the older parts of Iceland have been measured. It is found that a prism of basalt lavas with a cross-section of 80 km2 requires 3 to 6 km in thickness of dyke feeders. Extending these figures, for a prism of lavas 10 km thick with the present width of Iceland, a dilation of 200 to 400 km of dyke feeders is necessitated. While a dilation of this order is much less than the amount needed to separate America from Europe, it at least shows how substantial amounts of dilation could be achieved by dyke injection.