El Hierro is an island born of fire. As the most western of the Canary Islands, its young volcanic landscape is made up of a variety of craters and lava flows. But the island itself is merely the tip of a volcanic system rising up from the deep ocean.
Off the south coast of the island, the research vessel Poseidon - operated by Germany's GEOMAR Helmholtz center for ocean research Kiel - is positioned exactly above the submarine volcano. Onboard is an international team of scientists who have gathered to investigate the youngest crater, about 90 metres below.
"So the Canary Islands are what we refer to as a hot spot, a place where very deep melt from the mantle is making it to the sea floor and we're looking at a location which has a high density of volcanic centres. If you look on the island behind us you can see that there are as many as 30 or 40 small volcanic cones where magma has made it to the surface. We're here investigating the volcanic and hydrothermal activity at one of the sites that erupted in 2011. We want to know what are the long term impacts of such an eruption and how long does the volcano stay hot and could it erupt again", says Mark Hannington, a Canadian marine geologist working for GEOMAR.
El Hierro may seem calm and peaceful now but that certainly wasn't the case in 2011. Alerted by their seismic readings, geologists rang the alarm bell about an imminent eruption. The otherwise sleepy town of La Restinga - a haven for fishermen and dive tourists - was completely evacuated. In October 2011, the volcano finally erupted, not on land but in the ocean.
These images - filmed at a submarine volcano in the Pacific - show what the scene may have looked like under water.
As sulphur and other gases flowed from the volcano, the ocean off La Restinga turned green. Unique porous rocks appeared floating on the water surface and were named after the fishing port nearby: restingolitas.
After close to five months, the volcanic activity ceased and peace returned to El Hierro. More than four years later, seisomologists from the GEOMAR team are checking to what extent the earth here is still trembling.
"We set up devices called seismometers here, passive instruments which continuously register any seismologic tremors at different sites around the island. Our primary goal is to better understand the deformation still taking place here. For example the island has been liften by several centimetres since 2011. And even when it has been very quiet here for some time and the eruption is long over, there is still a low level of microseismicity. Every other day, there are small events, the strongest are about two to three in magnitude but they are certainly detectable", says Dietrich Lange, a German seismologist working for GEOMAR.
Because the island of El Hierro is simply the tip of a volcanic system otherwise covered by the sea, there is much to be learned from studying the geology exposed on land. Mapping the geological features here can help to interpret and predict the landscape underneath the ocean.
"What we do every day involves a lot of hiking to cover a lot of ground and just looking at the different features we see so the different kinds of lava flows, different flow morphologies and different ages of flows and also just documenting the different features we see. So different volcanic cones or landslide features and in that way we put together the geological map", says Melissa Anderson, a Canadian PhD student in geology at GEOMAR.
"On top of my satellite base image, I overlay tracing paper and that's where I draw on my contacts between different features that I see as I am hiking. [..] So this provides ground truthing as we call it for the different features we see on land that also occur on the sea floor."
Out at sea, the scientists are using a small submersible called JAGO, to take a close and personal look at the newly formed landscape under water.
"JAGO is Germany's only manned research submersible. We can dive to a maximum of 400 metres with two people onboard. Of course JAGO carries lights because it gets very dark at depth. We have a robotic arm to take samples...I always feel privileged to go to places where no- one has been before", says Jürgen Schauer, the pilot of the JAGO submersible.
"It's very quiet and it's very serene, especially when you get below the surface and it gets very calm and it's almost like descending into a dream because it's getting dark as you go down, the... it's a world that you are not normally in so it is very dream like and when you're at the bottom of course it also gets very exciting, it gets very intense. You're not the least bit concerned about being claustrophobic or being cold or being hungry or any of those things they just disappear because you are absolutely focused on what you can see", says expedition leader Mark Hannington.
"I think there have only been a few volcanic eruptions in the history of mankind which people have actually been able to see. And even if it has already been four years since the eruption here, it's very special to see the results of this recent eruption", says Sven Peterson, a German marine geologist at GEOMAR.
Scientists can stay down in the submersible for hours allowing them to explore the underwater landscape. Meanwhile, the support team at the surface closely monitors their progress and guides JAGO's navigation along the complex topography.
"So we use a manned submersible because as geologists we need to get that third dimension. Being able to look in three dimensions is extremely important and also for sampling. It's much easier for the pilot of the submersible to collect a sample if you are close to it", says Mark Hannington.
The scientists in JAGO collect samples of rocks as well as fluids that are still being emitted from the volcano.
"These are all the smoking gun of the volcano, they tell us the condition of the volcano, they tell us how active it is, they tell us what elements, what minerals are being extracted from the volcano and being precipitated at the sea floor and in the water column", says Mark Hannington.
Just what exactly is happening to the sea water is the research subject of two Canary Island scientists. They have been monitoring changes in temperature and chemistry at this site ever since 2011.
"We have installed a series of sensors in JAGO which has allowed us to constantly measure all of the changes we might see in this zone. In addition, we have also brought an integrated Niskin bottle to take water samples and also two teflon samplers which have enabled us to sample directly in the zone where we think maximum emissions are still being produced so that we can measure pH and iron", says Magdalena Santana-Casiano, a chemical oceanographer from the University of Las Palmas de Gran Canaria.
Most of El Hierro's south coast has been set aside as a marine reserve established by the local fishermen themselves. The emissions from the 2011 eruption killed off a significant number of fish in the area. But life here has made a spectacular comeback and populations of fish and other marine animals have bounced back to former strengths.
"So the impact of the volcano has been positive in the sense that these waters are generally poor in nutrients which we call oligotrophic waters. So the emissions have brought more nutrients, more iron and this has benefited the area. And overall this has positively affected the organisms", according to Magdalena Santana-Casiano.
The rock samples brought up by JAGO will be catalogued, packaged and taken back to the lab for analysis. This will include investigating their internal structure and their mineral composition.
The findings from this expedition will shed more light on what is happening at El Hierro but will also resonate on a global scale.
"So our overall objective here is to better understand the impact of volcanism in the ocean. More than 80 percent of volcanic activity on the planet is actually in the ocean not on land and so the opportunity to study a volcano that has erupted gives us a much better sense of the impact that that process has in the ocean environment. And we take this one observation point and we multiply it a hundred thousand times to get a better picture of how this might be impacting the oceans at a global scale", says Mark Hannington.
Among the finds made on this trip is the discovery that the youngest crater from the recent eruption is still emitting warm water heated by the magma below it.
For the time being, it's uncertain when the volcano here might erupt again. But the present research has already succeeded in bringing some of El Hierro's secrets to the surface.
ENDS