One of the geothermal vents in Mt Tarawera's Raupo Pond Crater came alive for the first time in 35 years last month, according to GeoNet.
The Mud Rift feature -- a 6m-wide, 36m-long, 15m-deep vent formed in 1906 that has been lying dormant since 1981 -- was activated sometime between May 17 and 20 this year.
A blog on the GeoNet website suggests the eruption was a fleeting event, and involved fluids flooding into the vent and causing "stress and browning off" of surrounding plants.
Damaged vegetation following the eruption (Supplied)
It says the eruption was mainly steam-driven, and involved plenty of water, creating what has been likened to a "muddy geyser".