The outside of a crater on Whakaari/White Island has collapsed, signalling "continuing unrest" on the island.
GNS volcanologists last week undertook observation and gas measuring flights over the Bay of Plenty volcanic island, which famously erupted in December 2019, killing 22 people.
According to a new report from volcanologist Craig Miller, in the time between two flights, "a small collapse occurred in one of the craters", which was active in 2019. It was confirmed dilute ash emission has ceased.
Miller wrote that during a gas measuring flight, volcanologists witnessed "geysering" from a small, grey-coloured pool on the south side of the crater.
"A little over an hour later during an observation flight, the pool was gone, and a collapse pit was present. The observation flight also established a larger collapse structure was present in the crater, but it is not clear exactly when this occurred."
The collapse activity "poses no immediate hazard", but does highlight how the "shallow crater environment remains dynamic and is changing in response to pressure variations beneath the active craters", Miller said.
"This is a sign of continuing unrest."
Miller said the "formation of collapse craters" on the island was common in the past and thought to be caused "by either withdrawal of liquid beneath the crater or the removal of fine-grained ash during recent ash emissions".
"Gas emissions have declined since the last measurements and vent temperatures are also lower at around 290C. The water level in the lake has receded slightly in the past few weeks. Volcanic tremor remains low."
The volcano remains at alert level 2, which is "associated with volcanic unrest hazards (including discharge of steam and hot volcanic gases, earthquakes, landslides and hydrothermal activity), the potential for eruption hazards also exists and eruptions can still occur with little or no warning".
Just this week, Mt Ruapehu's alert level was elevated to level 2 after rising temperatures and strong tremors were recorded.
