Scientists are raising the alarm at Mount Ruapehu over rising levels of toxic gases, a warming crater lake, and multiple small tremors in recent weeks.
GNS has placed the volcano at Alert Level 2 and the Department of Conservation has put a two-kilometre exclusion zone around the lake.
Climber William Pike was badly injured on Mount Ruapehu when it erupted unexpectedly in 2007.
He speaks to Māni Dunlop.
