Science agency GNS detected the low-energy explosions on Whakaari / White Island on Tuesday. Photo / File
A series of "small steam explosions" were detected on Whakaari / White Island yesterday.
Science agency GNS detected the low-energy explosions using seismic and acoustic air pressure sensors at the island.
They occurred at 3pm on Tuesday - and were short-lived, lasting about 30 minutes, the agency said.
At least 20 individual pulses occurred, which may have produced "minor traces" of ash near the vent for a few minutes.
MetService's satellite images didn't detect any ash in the atmosphere, it said.
Meanwhile, images from the island's webcam suggested more vigorous pulses of steam could have come from the active vent of the volcano at the time, GNS said.
Activity has since returned to a low level, it said. The island's volcanic alert level remains at 1 and the aviation colour code will stay "green".
"While Volcanic Alert Level 1 is mostly associated with environmental hazards, eruptions can still occur with little or no warning."
The lowest alert level is 0, classed as "no volcanic unrest". Level 1 means "minor volcanic unrest".
Primary hazards of alert level 1 include discharge of steam and hot volcanic gases, earthquakes, landslides and hydrothermal activity.
GNS volcanology team leader Nico Fournier said explosions like these have not been common since the December 9 eruption last year.
"But we have seen these many times in the past on the volcano. For example during 2012/13.
"These small steam explosions can be difficult to spot on the webcams and we only get to detect them thanks to our seismic and acoustic monitoring sensors on the island."
Whakaari/White Island erupted on December 9 last year at 2.11pm, claiming the lives of 22 tourists and tour guides.
There were 47 people on the island when it erupted. Many survivors were severely injured.
It's understood the crash involves a motorcycle and car.