Sulphur dioxide levels from Mount Tongariro have dropped significantly since the eruption on 6 August.
GNS Science says the most recent flight over the mountain showed sulphur dioxide emissions of 380 tonnes per day, down from just over 2000 tonnes per day three days after the eruption.
It says conditions have not been good enough to measure carbon dioxide and hydrogen sulphide concentrations in the volcanic plume.
GNS says field teams have been on the mountain taking gas samples and collecting data from three seismographs that survived the eruption.
Another new seismic station has been installed.