Iceland's government meteorological office is warning that a "significant" volcanic eruption is likely in the next few days.
Forecasters believe magma is forcing its way between rocks of the crust beneath Grindavík, a town of more than 4,000 people southeast of Iceland's capital Reykjavik.
The town was evacuated on Saturday, at which time experts weren't sure how the magma was likely to behave. By Monday, measurements indicated the greatest upwelling of this magma was less than three miles outside Grindavík.
Forecasters have recorded close to 2,000 earthquakes since midnight on local time on Sunday, which have cracked roads and shoved the ground as much as three feet upward in places.
Most of the quakes have taken place north of the town, at the same depth that magma is intruding.
Iceland evacuates residents over threat of volcanic eruption
Authorities also raised their aviation alert to orange, indicating an increased risk of a volcanic eruption.
Officials decided Monday that residents could return to the area long enough to "retrieve vital items, pets and livestock."
The Reykjanes Peninsula, where Grindavík is located, is known for its seismic activity.
The North American and Eurasian tectonic plates move apart from each other underneath Iceland, giving magma more opportunities to reach the surface.
In 2010, the volcano Eyjafjallajokull erupted and launched a cloud of ash 30,000 feet high that snarled air traffic across Europe for most of a week.
A damaging earthquake struck the peninsula in February of 2021.
