Lava is now visible on the surface of Whakaari/White Island, but there is no greater possibility of an eruption.
GNS Science said magma that it expected was just beneath the floor of the crater has now risen to the surface.
"It remains very unlikely (1 percent chance) that there will be another eruption in any 24-hour period during the next four weeks," duty volcanologist Craig Miller said.
The alert level is still at level 2, and the volcano remains in an elevated state of unrest.
"Although very unlikely, an explosive eruption from the active vent area remains possible and could occur with no precursory activity.
"This style of eruption could be driven by the collapse of unstable material behind the vents, or by a marked decrease in gas emissions allowing water from the reforming crater lake or geothermal system to enter the active hot gas vents.
"Apart from minor ash emissions on December 23rd and 26th, no significantly sustained or strong eruptive activity has been observed since the December 9th eruption."