In recent days, however, some unsettling measurements have been recorded: The shaking has moved to the north. Because most of the earthquakes in that area have, up until now, occurred at depths of more than ten kilometers, an eruption is not expected in the area, the local authorities have said. The magma seems to be contained in the depths thus far.
If the lava was being spewed in shallower water, there would be a danger of large steam explosions, says to Ramon Ortiz, the science advisor to the local government. But there are no fears of large eruptions on land according to Spain's National Geographic Institute (IGN). The only risk is in the immediate vicinity of the eruption site, where there may be lava flows and rocks flung into the air. Still, many of the nearly 600 residents of the fishing village of La Restinga on the southern tip of the island have now returned home after being evacuated two weeks ago.
A Major Eruption?
The risk of large, explosive eruptions in the Canary Islands, however, "should not be neglected," Sobradelo and her colleagues insist in their study. The frequency of their occurrence cannot currently be estimated. But even the most momentous outbursts of the past few centuries remained localised. In 1706, lava from the Pico del Teide volcano hit Tenerife, burying the port town of Garachio in the northwest of the island where massive black boulders now form the remnants of the lava flow. On Lanzarote, lava poured through villages in the north of the island from 1730 to 1740 and again in 1824. La Palma has experienced more than a hundred eruptions in the past 20,000 years; most recently in 1971 when a flow of lava ran into the sea.
El Hierro is the youngest of the Canary Islands, appearing above the surface of the sea just over a million years ago. As such, it is likely its magma reservoir may still be very large; geologists suspect it is around ten kilometers below the seabed -- most of the tremors have occurred at this depth. The last confirmed eruption was in 550 BC, although there are also disputable reports of an event in 1793.
In the eastern Canaries, on the other hand, supplies of lava have largely run out; they have already been far removed from the magma source. On Lanzarote and Gran Canaria, volcanic activity has already lasted 15 million years, on Fuerteventura 20 million. Although there has not been an eruption on Fuerteventura in the past 20,000 years, the volcano is still considered active -- unlike La Gomera, which seems to have run out of fresh magma. The island is expected to be spared from any future volcanic eruptions. It pays a price for this, however -- without any new lava, La Gomera will be washed away by rain and sea, and eventually, over the course of millions of years, will gradually sink back into the ocean.
Only fresh magma secures the existence of the Canaries; it was volcanic eruptions which allowed the islands to grow above the water in the first place. The sea is already at work trying to reclaim the land. Coastal roads have repeatedly had to be moved inland after being battered by floods. But the recent underwater lava eruptions could be creating new land near El Hierro, and residents are waiting eagerly to see if it will grow beyond the surface.