In our continuing effort to monitor geo-physical conditions that could affect us we must once again elevate the alert for a potential East Coast tsunami related to a potential of a major eruption of El Heirro. This is not to say an eruption is eminent, however both the presence of multiple HARMONIC quakes and rapid island bulging indicates that El Heirro is not as stable as previously thought.
It has been a few months now since the eruption at El Hierro in the Canary Islands was declared “over”. There may be some passive degassing on the seafloor from the new vent that formed at depth to the south of the island, but things had settled down. Even the people of Restinga were putting the eruption in the past, with both webcams taken offline and the guarantee of €600,000 (~$750,000) from the government to aid fishermen whose livelihoods had been altered by the closed fisheries. However, with any active volcano, it can be difficult to predict when exactly an eruptive cycle is truly done.
However starting late last week, seismicity under the island has resumed and its manifestation is very similar to what we saw last summer during the lead up to the eruption of El Hierro in October 2011. Over 50 earthquakes have been recorded at El Hierro, some as large as ~M3.5 and AVCAN thinks that the new seismicity suggests that magma is moving in the same conduits as the fall 2011 activity. The earthquakes are, as of June 23, were still deep – upwards of 15-25 km below the surface. This likely supports the idea that there is new magma entering the El Hierro system at depth. Now, last summer it took months of constant seismicity before we saw any surface manifestation (the submarine vent at ~88 meters depth), so we may not know if this new intrusion of magma will lead to new eruptions until the fall.
Then by last Monday, June 25th, the unusually strong earthquake swarm under El Hierro Island continued, harmonic volcanic tremor had reappeared short time ago at about 16h10 UTC. The tremor, a low-frequency ground vibration, is thought to be caused by moving magma. It had been strong last Sunday and Monday and correlated well with a southward propagation of earthquake locations, suggesting that magma at about 20 km depth flew from underneath the El Golfo area towards the EL Julan (south) coast, in a similar way as before the Oct 2011 eruption, but became blocked there, and did not reach the southern rift zone near La Restinga. After the cease of tremor in the afternoon, earthquakes still continued at high rate, marking a record figure with over 180 quakes larger than M2 Sunday alone, and more than 150 quakes larger than M1.5 on Monday. In other words, pressure continued to cause wide-spread rock fracturing underground and cause small intrusions of fluids. Now, the re-appearance of tremor could mean that magma is moving again somewhere underneath the island. Where to and whether or not it might reach the surface and initiate a new eruption is difficult to know at the moment. It is essential to continue to monitor location and magnitude of earthquakes.
AS of Friday, following days of almost continual earthquakes, residents of the small Canary island of El Hierro are once again living in fear of a volcanic eruption as their island begins to lift. According to the National Geographic Institute of Spain, increases in seismic activity on the island has seen literally hundreds of earthquakes, known as a swarm, shaking the island and gradually increasing in strength since June 25. Around 750 earthquakes have been recorded although few have been strong enough to be felt by the residents until the last two days The island has been placed on yellow alert by the security committee in charge of operations as the earthquakes increase. The largest so far was registered at 4.0 on the Richter scale on Wednesday June 27. More frightening for the approximately 10,000 residents is the fact that a bulge has developed in the island, lifting it five centimetres in four days. Whereas the volcanic activity of 2011 was based out at sea, this time the magma appears to be forming right underneath the island and the pressure is building. Scientists on the island are using the position of the earthquake epicentres to try and work out where the magma from the volcano will come to the surface.The longer it takes to find a vent, the more the pressure from the magma will grow and the larger any possible eruption is likely to be.
Earthquake Report says that PEVOLCA (Civil Protection from Volcanic Risk) has said that there is an acceleration in the flow of magma, with a “clear process of inflation”. As reported by Digital Journal on June 25, the island suffered serious seismic activity last year, resulting in an undersea volcanic cone as can be seen in the video. However, over time, the activity died down and it was thought by experts that was the end of the event. The research vessel ‘Hesperides’ which had been investigating went home and the live cameras were turned off. Now the ‘Hesperides’ is hurrying back to the island but the cameras have not as yet been turned back on. The website Decoded Science, in an article by Jennifer Young, explains how magma chambers work and how scientists are processing information from volcanoes to learn more about predicting possible eruptions. It is this activity that the scientists on the ‘Hesperides’, in conjunction with those on the island itself, will be studying in an effort to try and predict if and when the volcano under El Hierro will erupt. Official reports have been few and far between and the Spanish media has concentrated rather more on the football and the economy than the volcano growing under one of Spain’s most popular holiday destinations, just as the season gets into full swing.