El Hierro Eruption Continues, but not Likely to Form new Island

By Erik Klemetti
October 17, 2011

The eruption off the southern coast of El Hierro in the Canary Islands looks to be subsiding and from the sound of it, the focus of the activity is slowly migrating into shallower water. However, so far all the activity has remained submarine, producing an impressive discoloration of the ocean as tephra and volcanic gases are released from the vents. Check out this image of the eruption seen on October 16 (courtesy of Dave Mayer):

An EO-1 image of the submarine plume from El Hierro in the Canary Islands. Image taken October 16, 2011 and courtesy of NASA. Image processing by Dave Mayer and annonation by Erik.

In the image, you can clearly see the plume of the eruption spreading westward from the main vent area, which is just off the southern tip of the island. It looks like the main fissure might be 2-3 km in length and is close to on strike with the rift axis for the main El Hierro edifice. Ramon Ortiz, coordinator of a government scientific team, said that if/when the eruption reaches shallower water, we should expect to see the surface water start to steam, followed by explosions of steam and magma and finally the emergence of an island. If you want to see how that might look, just look at images of the 2009 eruption of Hunga Tonga Hunga Ha'apai in Tonga to see how a submarine eruption in shallow water behaves, producing "rooster tails" tens to hundreds of meters tall. There is already dark pumice spotted floating on the surface of the ocean (see below) along the southern coast of the island as well (and these clasts generated a lot of discussion amongst the geotweeps).

Dark pumaceous clasts spotted floating on the ocean near the eruption at El Hierro, October 14, 2011. Image by IGN.

As for the residents of La Restiga and the southwestern coast of Hierro, the local government allowed them to return to their homes on Saturday, however on Monday, many residents are still wary of returning. It does seem like there is a lot of confusion amongst the residents of exactly what the nature of the eruption will be as many have voiced concerned about returning when the volcano is "about to explode". This activity is not likely to produce a large, destruction event like the 1902 Pelee pyroclastic flow, but should be more like Surtsey or, when it reaches land, like the 1971 eruption at La Palma (although possibly larger in volume), which were tourist attractions rather than death. The activity will be monitored closely, including the installation of hydrophones in the harbor to listen for new explosions on the seafloor (note: some of this graphic is a little scientifically dubious, like the area labeled "magma") if the eruption continues to propagate towards land. However, the eruption, even if it comes closer to land, is not a major hazard to people on the island beyond the potential for bombs/ash to be thrown on land or, if the eruption makes it to land, lava flows. The Spanish government has closed the port at La Restiga due to the volcanic debris and air traffic is restricted over the eruption and there is also concern about how the eruption might effect marine reserves around Hierro. If an new island does emerge from this eruption and has any permanence, there will be the question of exactly whose island it is and what to name it – but Nemesio Pérez of the Instituto Vulcanológico de Canarias seems to think that there isn't enough magma to produce any new island off of El Hierro.

One thing that is remarkable about this eruption is how the towns on the south coast of El Hierro are nestled between all these volcanic vents. I saw an image of the discolored sea surface from the eruption with a hamlet on the coast in the background. I see at least ten small scoria/cinder cones in the area around the town (see below), all evidence of the volcanic legacy (and recent legacy at that to preserve these cones) along the southern coast of El Hierro.

The discoloration of the Atlantic Ocean off of El Hierro due to the ongoing eruption. Note the abundant cinder/scoria cones on the island near the small town, meaning an eruption in this area isn't unexpected. Image by IGN.

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