El Hierro. Photo: Creative Commons
As I am gearing up for my yearly work trip to the Canary Islands, the 2011–2012 submarine eruption off the island of El Hierro is on my mind.
The Canary Islands are a group of volcanic islands offshore northwest Africa, and part of Spain. Across millions of years, the islands have undergone numerous eruption cycles and partial collapse events.
This image of El Hierro was acquired by one of the Copernicus Sentinel-2 satellites. on 9 December 2023. Photo: Wikimedia Commons
Eruptions below the ocean can be impactful, and this includes the unrest period. Unrest is the activity before the eruption itself. This includes seismic activity, the earthquakes that occur as magma, hydrothermal fluids, and gases, move through the brittle crustal rock, breaking the rock as it goes and possibly activating nearby faults.
Janine Krippner
This unrest can profoundly disrupt communities, even when the eruption ends up occurring below the ocean.
This was the case leading to the El Hierro eruption. For the communities living through this unrest, the uncertainty is its own kind of crisis. There is no way of knowing where the new vent will open, as is the case for our own Auckland Volcanic Field. We also cannot know exactly when, though that becomes clearer closer to the start of the eruption. The other unknowns are how big the eruption will be, then how long it will last. Although estimates can be made for those too with the right monitoring and information.
Unrest was first detected in July 2011. The volcanic crisis had begun. The seismicity was largely below the island, caused by the intrusion and accumulation of magma that was centred around 10-15 km below the surface. This resulted in around 27cm of uplift.
As volcanologists, we are tasked with understanding the range of scenarios and helping decision makers, responders, and communities to prepare for activity with that uncertainty. This is a tough job with high stakes, and with real impacts for the people who live there. We can all imagine that not knowing if a volcano were to erupt below your home or business for weeks on end would leave scars.
In September the seismicity showed magma migrating southwards. Magma doesn’t just travel straight upwards in settings like this. Seismicity was also accompanied by ground deformation, the slight movement of the surface from the magma accumulating below.
When the main vent opened on October 10, located 1.8 km off the southern coast at 900m below sea level, the damage had been done. These are complex and difficult situations for everyone involved, especially when there hasn’t been an eruption in recent memory.
Volcanoes are complicated, and so are people and society. It takes scientists and communities working together to help reduce the impacts of these events. The social sciences are critical to effectively doing so.
The eruption ended on March 5, 2012, and volcanologists go on to spend years working on the data to learn more about how these eruptions progress. There is always a lot to learn about the volcanic system, but also the human side of these events and how we can better support our communities next time.
And there will always be a next time.
El Hierro. Photo: Creative Commons
