Iceland’s president said the country is battling “tremendous forces of nature” after molten lava from a volcano in the island’s southwest consumed several houses in the evacuated town of Grindavik.

President Gudni Thorlacius Johannesson said in a televised address late on Sunday that “a daunting period of upheaval has begun on the Reykjanes Peninsula”, where a long-dormant volcanic system has awakened.

A volcano on the peninsula erupted for the second time in less than a month on Sunday morning. Authorities had ordered residents to leave the fishing town of Grindavik hours earlier as a swarm of small earthquakes indicated an imminent eruption.

Geophysicist Magnus Tumi Gudmundsson said on Monday morning that the eruption had “decreased considerably” overnight, but that it was impossible to say when it would end.

Grindavik, a town of 3,800 people about 50km (30 miles) southwest of the capital, Reykjavik, was previously evacuated in November when the Svartsengi volcanic system awakened after almost 800 years.

Since then, emergency workers have been building defensive walls that have stopped much of the lava flow from the new eruption short of the town.

There have been no confirmed deaths as a result of the eruptions, but a workman is missing after reportedly falling into a crack opened by the volcano.

Iceland, which sits above a volcanic hot spot in the North Atlantic, averages one eruption every four to five years. The most disruptive in recent times was the 2010 eruption of the Eyjafjallajokull volcano, which spewed clouds of ash into the atmosphere and disrupted transatlantic air travel for months.

The latest eruption isn’t expected to release large amounts of ash into the air. Operations at Keflavik Airport are continuing as normal, said Gudjon Helgason, spokesman for airport operator Isavia.