Confirmation of central volcanoes off the Icelandic coast

THE Icelandic shelf and slope region occupies much of the transition zone between the complex Icelandic hot spot and more uniform ocean-ridge areas to the north and south. This transition zone is relatively little known geologically, but in this communication we summarise some recent observations on the nature of its basement. It is well known¹ that the shelf is generally narrower off the eastern half of Iceland than off its western half. This is most obvious south of Iceland, where the shelf width changes suddenly at the eastern volcanic zone; the insular slope is also steepest off south-eastern and north-eastern Iceland. Recent geophysical surveys^1,2 in the southern and south-eastern shelf area have indicated the presence of an abrupt basement scarp now covered by sediments, 5-14 km inside the bathymetric shelf break (Fig. 1). This scarp is at least 1 km high and only a few km in mean width. No such basement scarp is indicated in comparable surveys conducted so far off western Iceland^1-3; north-east of the island, detailed data is not yet available.