Thousands of small earth tremors around Spain’s Canary Islands has put authorities on alert for a volcanic eruption.
An official said on Thursday that there was “intense seismic activity” in the area off north-west Africa.
Authorities have detected more than 4,200 tremors in what scientists are calling an “earthquake swarm” around La Palma Island since last Saturday.
An earthquake swarm is a cluster of quakes in one area during a short period and can indicate an approaching eruption.
But officials said they had no indication that an eruption was imminent, and a scientific committee monitoring the activity said that the number of tremors and their magnitude had fallen on Thursday.
Even so, the Scientific Committee for the Special Civil Protection Plan and Emergency Response for Volcanic Risks warned there could be a rapid, renewed surge in quakes and kept the public warning level on yellow, Spanish news agency Europa Press reported.
Volcano warnings are announced in accordance with the level of risk, rising through green, yellow, orange and red.
The committee reported that ground depressions of up to 10 centimetres deep have formed in an occurrence often attributed to magma movements.
Before a volcano erupts, there is a gradual increase in seismic activity that can build up over a long time.
The Canary Islands Volcanology Institute said that by Thursday, 11 million cubic metres of molten rock had been pushed into Cumbre Vieja, a dormant volcanic ridge on La Palma where the most recent eruption occurred, in 1971.
The strongest quake so far was magnitude 3.4, the institute said. La Palma has a population of about 85,000 people.
The institute has been telling staff on the island to monitor any changes, including testing the water in wells.
The eight Canary Islands are a volcanic archipelago, 100 kilometres from Morocco.