The surge in the number and intensity of earthquakes in the past week has prompted officials from the Instituto Geografico Nacional (IGN) and The Canary Islands Government to raise the alert level for the Hierro volcano to ‘Yellow’, the highest alert status since the unprecedented earthquake swarm commenced in mid-July.

Hierro, a shield volcano, has had a single historic eruption from the Volcan de Lomo Negro vent in 1793. The eruption lasted approximately one month and produced lava flows.[Irish

Seimsic Surveys

The Canary Islands Government commenced an in-depth geological survey of El Hierro earlier this month in an effort to determine the source of an earthquake swarm. The Government raised the volcanic risk level to ‘Yellow’ last weekend after a surge in seismic activity

The IGN announced on Saturday that the number of earthquakes felt by the local population (approx 10,000) has reached 55. The strongest of the tremors, which have been recorded at depths between 10km and 15km, measured 3.8 magnitude on the Richter Scale.

Spain’s national seismological agency warned the local population to be prepared for any possible future increase in volcanic activity. The agency noted, however, that the majority of earthquakes recorded during recent days have been centred to the south of the island in Las Calmas Sea. Previous to this, the vast majority of the tremors were recorded in the northwest of the 278.5-square-kilometre island at El Golfo.

Evacuations

Over 150 earthquakes were recorded on the smallest of the Canary Islands during Tuesday prompting officials to evacuate some local residents, shut El Hierro’s main tunnel, and close local schools.

A surge in seismic activity on Tuesday prompted the Spanish Civil Guard (Guardia Civil) to advise almost 50 residents of the municipality of La Frontera to leave their homes because of landslide fears. Two units of the Spanish military’s emergency intervention unit (EMU) were also placed on standby to depart the nearby island of Tenerife  to assist in the possible evacuation of hundreds of other El Hierro residents.

Meanwhile, the island’s main tunnel (Tunel del Golfo), which links Frontera to Valverde, was shut forcing motorists to travel across the 280-sq-km island via a mountain road. The Cabildo de El Hierro also ordered the closure of schools on Wednesday.

Eruption would have “low explosion value”

Speaking to the El Pais newspaper, volcanologist Juan Carlos Carracedo suggested that an eruption on El Hierro would “not be a major surprise”. He explained: “It is the youngest of the Canary Islands. There is a ball of magma which is rising to the surface and it is stationed at the limit of the earth’s crust. At the moment we do not know if that ball of magna will break the crust and cause an eruption.”

IGN Director, María José Blanco said that any eruption on El Hierro would most likely have a “low explosion value”. He added that an imminent eruption is unlikely.