Thousands of earthquakes have been caused by a massive buildup of magma in a 15 kilometer rift.
The gorge is about 3.5 kilometers northwest of Grindavik, a town of 4,000 on the Reykjanes Peninsula that has been evacuated.
How likely is an eruption?
Iceland’s Met Office said on Wednesday that the “probability of an eruption is still considered high.”
Vidir Reynisson, head of Iceland’s Civil Protection and Emergency Management Agency, said experts are “really concerned about all the houses and infrastructure in the area.”
John Smellie, a volcanologist at Britain’s Leicester University, said lava “flows relatively slowly, and people can generally at least drive away from it or run from it.”
He said this means deaths are unlikely.
The eruption can be more intense if it blows through ice or water.
If it occurs in the southern tip of the gorge, which is underwater, it could cause ash clouds that could affect flights at Iceland’s international airport.
Other than the 2010 Eyjafjallajokull eruption?
An eruption is not expected to have as much impact as that of the Eyjafjallajokull volcano in 2010.
That eruption shot huge amounts of ash into the atmosphere, forcing the cancellation of about 100,000 flights and stranding more than 10 million travelers.
It exploded through 200 meters of ice, becoming “very violent,” Smellie said.
The interaction with the water created more fine ash particles that would then drift through Europe.
The latest eruption threat is a “totally different situation,” Smellie said.
Marc Reichow, a geochemist in Leicester, said it was “unlikely to happen this time as there is no substantial amount of ice in the area where an eruption is expected to occur.”