Canary Islands Government Raises El Hierro Volcanic Risk Level

The Canary Islands Government has raised the alert level for the El Hierro volcano in the Canary Islands (Spain) to 'Yellow', the highest alert status since an unprecedented earthquake swarm commenced in mid-July.

Spanish seismologists, accompanied by the President of the Cabildo de El Hierro and the Minister of Security and Emergency Area, held a press conference on Sunday to reassure the 10,000 residents of the smallest of the Canary Islands that the raising of the alert level does not indicate that an eruption is imminent. They indicated, however, that the number of volcanic earthquakes detected beneath El Hierro continues to increase.

© Google maps
El Hierro (circled) in The Canary Islands.

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.

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 unprecedented seismic activity commenced on 19 July (the activity was first reported by iWeather Online on 26 July). In excess of 6,750 earthquakes have been recorded up to Monday, 26 September 2011. More than 50 earthquakes were recorded between midnight and 6:00 a.m. GMT on Monday alone. The earth tremors have ranged between 1 and 3 magnitude, the National Geographic Institute (IGN) reported.

The vast majority of the tremors have been recorded in the northwest of the 278.5-square-kilometre island at El Golfo, the location of a massive landslide that created a 100-metre high tsunami almost 50,000 years ago.

Speaking to the El Pais newspaper during the weekend, 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."

Earthquake Swarms

Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time. The length of time used to define the swarm itself varies, but the United States Geological Survey (USGS) points out that an event may last for days, weeks, or months.