GEOFF BENNETT: Scientists in Iceland say a major volcanic eruption could occur within days, but they are increasingly optimistic that it may spare a town 40 miles southwest of the capital, Reykjavik.

Special correspondent Malcolm Brabant has the story.

MALCOLM BRABANT: Listen to the roar of Mother Earth.

That's the sound of magma, molten rock, bubbling away beneath the town of Grindavik, causing hundreds of earthquakes a day.

ARI TRAUSTI GUDMUNDSSON, Geophysicist: The outlook is rather bleak, in my opinion.

MALCOLM BRABANT: Geophysicist Ari Gudmundsson: ARI TRAUSTI GUDMUNDSSON: The ground in Grindavik is still subsiding, but you cannot really make or prognosis how is eruption going to affect the town.

MALCOLM BRABANT: After being ordered to abandon Grindavik a week ago, its people have been allowed back to rescue key possessions.

The owners of this craft store worked quickly to salvage stock, while other residents like Ingibjorn Gretarsdottir awaited their turn.

INGIBJORN GRETARSDOTTIR, Grindavik, Iceland, Resident: I'm not sure about the town.

It looks awful.

My house is OK, but it's on the red area.

The earth has collapsed about one meter or something, so the lava is under our house.

We don't know if we're going to have a home or what.

EINAR DAGBJARTSSON, Pilot: It's hard to digest.

MALCOLM BRABANT: Pilot Einar Dagbjartsson.

EINAR DAGBJARTSSON: For the last four days, I have been just -- when I wake up after kind of bad sleep, you know, it's so worrying.

I check the news, check the news.

I have been expecting it to start.

But I am getting a little bit more hopeful that it's not going to erupt in the town.

MALCOLM BRABANT: If it happens, this eruption is not going to manifest itself in the classic way, from the top of a fiery mountain.

Instead, scientists expect lava will burst through fissures in the ground somewhere above a wide volcanic field.

Kristin Jonsdottir is the head of Iceland's volcanoes department.. KRISTIN JONSDOTTIR, Head, Icelandic Volcanoes, Earthquakes and Deformations Department: Every day, what we're seeing is a decline in the rate of earthquakes and also in the rate of energy release from the earthquakes.

However, this does not mean that an eruption is less likely.

We have actually seen a similar decline just before the onset of eruptions in Fagradalsfjall.

MALCOLM BRABANT: Fagradalsfjall is the volcano that erupted in 2021 after being dormant for 800 years.

That spectacular renaissance is being blamed for the current seismic activity, although the 1,200-feet-high crater appears to be sleeping.

With scientists monitoring the volcano, the priority of Prime Minister Katrin Jakobsdottir is the 4,000 displaced people.

KATRIN JAKOBSDOTTIR, Icelandic Prime Minister: We have put forward a bill to the Parliament to ensure the salaries for the inhabitants of Grindavik, at least for the next three months.

We are working to secure housing, because 1,200 homes, people do not have guaranteed housing.

So we are working on that.

MALCOLM BRABANT: Rikke Pedersen heads the Nordic Volcanological Center at Iceland University.

What sort of scenarios do you envisage?

RIKKE PEDERSEN, Iceland University: Currently, we have two main scenarios.

One is that the current deformation that we see on the surface will slow down, decline and eventually stop.

But maybe a more likely scenario, as it's looking now, the pressure rises enough for it to actually open a vent at the surface and an eruption will start.

MALCOLM BRABANT: So when the molten rock, the magma, reaches the surface and becomes lava and hot, does that mean that things are going to catch fire?

Is the town going to burn to the ground?

RIKKE PEDERSEN: Oh, of course, it really depends on where the fissure opens.

So the most likely area is several kilometers north of Grindavik.

MALCOLM BRABANT: That scenario threatens the Blue Lagoon, a volcanic grotto and a thermal spa beloved by tourists and currently closed.

The Icelanders are also trying to protect one of five geothermal power stations that generate electricity from underground heat.

Vidir Reynisson leads Iceland's civil defense units.

VIDIR REYNISSON, Director General, Icelandic Civil Defense: The barriers that we are building around the power plant is going quite well.

We are a little bit ahead of schedule in that.

So, the first phases of the barriers are ready.

So, even if we would have an eruption in the dike at this moment, we are -- we would at least to delay the lava flow to the power plant.

MALCOLM BRABANT: In 2010, another Icelandic volcano created an enormous ash cloud, causing the suspension of air travel in Europe and across the Atlantic.

How is this likely to compare to the eruption of Eyjafjallajokull?

I think I pronounced it correctly.

RIKKE PEDERSEN: Eyjafjallajokull is really not comparable to this at all.

So when an eruption commenced there in 2010 in the top crater, it interacted very directly with the meltwater from the glacier and creating a very violent and explosive eruption, so very fine-grain ash that could be carrying thousands of kilometers from the vent.

This is not at all what we're going to see if we have an eruption on land.

MALCOLM BRABANT: The residents of Grindavik wonder whether they will ever be able to return to what is for now a ghost town, where scientists are monitoring the seismic activity.

Volcano department spokesman Benedikt Ofeigsson: BENEDIKT OFEIGSSON, Iceland Meteorology Office: If an eruption will occur, it's probably within days, rather than weeks.

MALCOLM BRABANT: Like this geyser, Icelanders are waiting to see whether the latest seismic activity is nothing but a damp squib.

They're preparing for the worst, but hoping the volcano goes back to sleep in the land of the Northern Lights.

For the "PBS NewsHour," I'm Malcolm Brabant.