As New Zealand island volcano vents again, GeoNet warns: 'Eruptions in the next 24 hours are still likely'

The New Zealand island volcano that erupted two days ago vented more steam and mud on Wednesday, an increase of geothermal activity that continued to delay the recovery of victims' bodies.

With a police investigation underway after the White Island eruption that killed at least six people, with eight others presumed dead, the GeoNet seismic monitoring agency reported volcanic tremors in the morning hours.

“We interpret these signals as evidence of continued high gas pressures within the volcano,” the agency said. “The situation remains highly uncertain as to future activity. Eruptions in the next 24 hours are still likely to occur.”

What is a cone volcano? The science behind the deadly New Zealand eruption

Those killed, missing or injured came from around the globe to visit the island when tragedy struck Monday afternoon as steam and ash blanketed the popular tourist destination. The first confirmed death was of a local man, Hayden Marshall-Inman, a guide who had shown tourists around the island.

Bruce Bird, an acting assistant police commissioner, said officials were monitoring the situation hour by hour before proceeding with recovery efforts.

“Safety for our staff is a huge priority for us,” Bird said. “And we’ve got to get this right.”

Helicopter pilot Mark Law, however, questioned the delay.

“It would take 20 minutes to get out there. We know where they are,” he said, referring to the bodies. “Then we could bring them home.”

Here's what we know Tuesday:

Who was on White Island and how many people were killed?

Authorities have confirmed that 47 people were on the island when the volcano exploded just after 2 p.m. Monday.

Nine Americans, 24 people from Australia, two from China, four from Germany, one person from Malaysia, five people from New Zealand and two from the United Kingdom were on White Island, police say.

Some of those on the island were aboard the Royal Caribbean cruise ship Ovation of the Seas.

Five people were confirmed dead as crews rescued people from the island. A sixth person died in the hospital Tuesday. Eight people are missing and presumed dead. Crews flying above the island have seen "no signs of life," police said. About 30 remained hospitalized Tuesday.

Among the injured was Virginia couple Lauren and Matt Urey of Richmond on their honeymoon. The Ureys were part of the Royal Caribbean cruise.

Why were tourists on the island?

That's the question police will be investigating after increases in seismic activity had been recorded on White Island for weeks.

"These questions must be asked and they must be answered," Prime Minister Jacinda Ardern said in Parliament.

GeoNet, which tracks New Zealand's seismic and volcanic activity, raised its alert level on the island in November after increasing sulfur dioxide gas. Volcanic tremor also increased, and the agency wrote at the time that the island "may be entering a period where eruptive activity is more likely than normal."

Loÿc Vanderkluysen, a volcanologist at Drexel University, said he was surprised that tourists were on the island given the volcanic activity.

More on White Island eruption: Royal Caribbean cruise nearby, other travel effects

"Scientists seem to have been well aware that White Island was entering a phase of heightened activity," he said.

"Whakaari," as it is known in the Maori language, is New Zealand’s most active cone volcano, built up by continuous volcanic activity over the past 150,000 years, GeoNet said.

"About 70% of the volcano is under the sea, making this massive volcanic structure the largest in New Zealand," according to GeoNet.

Deputy Police Commissioner John Tims said Tuesday that police were opening a criminal investigation into the deaths that would accompany an investigation by health and safety regulators.

But hours later, police later said it was too early to confirm a criminal investigation and they were investigating the deaths on behalf of the coroner. Workplace health and safety officials in New Zealand have also confirmed they are investigating.

Is there still a risk the volcano could erupt again?

GeoNet's volcanologists said there was an "equal likelihood" of either no eruption or another smaller or similar sized eruption in the next day.

"There is a high level of uncertainty associated with this estimate and we are working to reduce that uncertainty. We also estimate the least likely scenario is a larger eruption," GeoNet volcanologist Geoff Kilgour said.

GeoNet had briefly raised the volcanic alert level to four, on a five point scale, on Monday, but lowered it to three, where it remains Tuesday.

What was it like on White Island during the eruption?

Survivors and rescuers described a chaotic scene. Those on the island ran into the water to protect them from ash and steam.

Many onlookers from boats just off the island captured horrific images of smoke billowing from the land.

"I could just see this plume of white and grey rising quite high and quite quickly," Geoff Hopkins, 50, told the New Zealand Herald. Hopkins was on a boat when he saw people rushing into the water. The crew turned toward them to provide first aid.

"They were just so massively burnt," he told the newspaper.

Russell Clark, an intensive care paramedic worker, said the island blanketed in ask looked like the Chernobyl nuclear disaster.

"I can only imagine what it was like for the people there at the time – they had nowhere to go," Clark told New Zealand broadcaster TVNZ.

Contributing: Doyle Rice, USA TODAY; The Associated Press.

Follow USA TODAY's Ryan Miller on Twitter @RyanW_Miller

This article originally appeared on USA TODAY: New Zealand volcano eruption: Why were tourists on White Island?