Rain from recent cyclones passing through the Bay of Plenty is believed responsible for White Island's crater lake refilling.
Scientists from a GeoNet monitoring team visiting the island last week noticed the change.
Volcanologist Brad Scott says the reappearance of the lake appears to be a response to the rainfall.
Scientists on a similar monitoring visit observed the disappearance of the crater lake in October 2016.
“The lake temperature is relatively cool at 27 ºC, and we were also able to sample the lake,” says Brad.
The refilling lake was last sampled in August 2017.
Temperatures of both the Dome vent in the active crater and Fumarole 0 on the Main Crater floor continue to decline, says Brad.
The Dome vent is now 128 ºC, down from 157 ºC in December 2017.
Fumarole 0 is down from 144 to 138 ºC. Spring and stream flows have also declined, which is consistent with the lower water level in the Crater Lake or following periods with no lake present.
The ground deformation survey also shows subsidence towards the Active Crater of 2-5 mm per month.
There was a small earthquake swarm near the island volcano over the weekend, but no changes in activity were apparent after the swarm. The largest earthquake was M3.3 at 11.37am on Saturday March 17.
“We have not detected any changes at the island related to these earthquakes,” says Brad.
“The volcano remains quiet. The monitoring team undertook a ground deformation survey, measured fumarole and vent temperatures, sampled springs and the Crater Lake. These activities are part of the routine monitoring undertaken at White Island every three months.
“These visits complement the seismic, acoustic, GNSS, web camera and gas data that are collected continuously.
“White Island is always capable of a new eruption at any time, often without any useful warning. We continue to monitor the volcano for possible renewed activity.”
The Volcanic Alert Level remains at Level 1. The Aviation Colour code remains Green.