Series of overnight steam explosions at Whakaari/White Island

A series of steam explosions have been observed at Whakaari/White Island early this morning - but scientists say activity on the off-shore island has returned to normal. Photo / Ben Fraser

A series of steam explosions have been observed at Whakaari/White Island early this morning - with some of the blasts of similar size to 2019's disastrous blow.

GNS Science volcanologist Brad Scott described the activity, recorded from 2.20am, as "short-lived, low-energy" steam explosions.

Like the December 2019 blast at the offshore Bay of Plenty volcano which killed 22 people and left more than 20 others injured, these eruptions occurred without warning.

"No observations were available from the island's webcams as it was still dark," Scott said.

"The overall series of pulses lasted for about 100 minutes and were of a similar size to those recorded on December 29, 2020."

Scott said volcanic tremor levels started to rise about 9pm on February 18, but ceased at about 5.50am today, as the explosions ended.

"These small events do not appear to have produced any traces of ash locally."

A gas flight was completed yesterday however showed no changes in gas flux or crater conditions from a month earlier.

"The level of seismic tremor had been slightly above background in the two days preceding the explosions but has since returned to background levels," Scott said.

"As a result, the Volcanic Alert Level remains at one and the Aviation Colour Code remains at green."

Volcanic Alert Level 1 indicated the primary hazards are those expected during volcanic unrest; including discharge of steam and hot volcanic gases, earthquakes, landslides and hydrothermal activity.

While that level was mostly associated with environmental hazards, eruptions can still occur with little or no warning.

"The main plausible triggers for a sudden eruption remain the collapse of unstable material in an active vent and the possible ingress of water underground on to the shallow magma body."

The island today essentially remains off-limits to the public, with no tours or sightseeing flights allowed.