The Department of Conservation says Mount Tongariro will probably remain closed for the next two to three weeks.
Ruapehu area manager, Jonathan Maxwell, told Checkpoint about 20 staff have been looking at data from the volcano but still don't know for sure when people can return.
Mr Maxwell says DoC is working with tourism operators and appreciates the economic impact of closing the Tongariro Alpine Crossing.
The track attracts more than 80,000 trampers every year.
GNS Science says there have been no more ash eruptions from the mountain but it is still emitting a significant amount of gas.
Scientists began analysing ash from Mount Tongariro on Thursday.
A volcanologist says initial findings suggest the cause of the eruption was quite different from the one in August.
Marco Brenna from Massey University says his team has gathered ash samples from the mountain and is taking them back to its lab in Palmerston North for further analysis.
Dr Brenna says the ash appears coarser than the material ejected in the last eruption, which suggests magma didn't reach the surface like it may have in August.
Although there is debate between Massey and GNS about whether magma reached the surface in August.
He says the next step will be to analyse the chemical makeup of the ash, looking for poisonous compounds like fluoride which can pose a hazard to drinking water and pasture for livestock.
GNS Science volcanologist Nico Fournier says it suspects this is the beginning of a series of eruptions and another one is likely in the coming months.
The eruption was for about five minutes at about 1.30pm and ash and steam was sent 4km into the air.
The top half of Mount Tongariro was shrouded in cloud on Thursday morning, making it difficult to tell how much steam is still billowing from Te Maari crater.
GNS Science surveillance co-ordinator Brad Scott told Morning Report the conditions inside the mountain indicate other eruptions are likely.
Those conditions include elevated gas levels and heat flows and more earthquake activity.
AAP reports the volcanic alert level stands at two, signalling minor eruptive activity and the aviation colour code had been decreased from red to orange, indicating that a volcanic eruption is under way, but with little or no ash being produced.
Mount Tongariro last erupted at 11.50pm on 6 August, for the first time since 1896 - 1897.