The country’s National Geographic Institute told reporters that dead fish were seen floating on the ocean surface above where the eruption emerged.
The institute’s scientists said they were not yet able to determine if the eruptions, at a depth of about 1,500 feet, were spewing lava or gas.
It now appears unlikely that the more than 9,000 tremors that have jolted El Hierro since July 17 will lead to another eruption on the island.
People who had left their homes over volcanic fears returned home, and officials announced they were going to reopen the islands’ most important road tunnel, which had been closed as a precautionary measure.
The island's only eruption in recorded history was in 1793, when it rumbled for about one month with flows of lava.