As the result of all the deep-sea surveys now available we know that the central rise of the Atlantic starts from Iceland as the Reykjanes Ridge with less than loon fathoms of water over it in most parts and runs south-westward until in 51° N.
The south coast is flat next the sea; but immediately underneath Vatnajokull there is a strip of gravel and sand, brought down and deposited by the glacial streams. The largest low-lying plain of Iceland, lying between Myrdalsjokull and Reykjanes, has an area of about 1550 sq.
On several occasions there have been volcanic outbreaks under the sea outside the peninsula of Reykjanes, islands appearing and afterwards disappearing again.
Earthquakes are frequent, especially in the districts which are peculiarly volcanic. Historical evidence goes to show that they are closely associated with three naturally defined regions: (I) the region between Skjalfandi and Axarfjdrllr in the north, where violent earth tremblings are extremely common; (2) at Faxafloi, where minor vibrations are frequent; (3) the southern lowlands, between Reykjanes and Myrdalsj6kull, have frequently been devastated by violent earthquake shocks, with great loss of property and life, e.g.