SfondoRuapehu is a complex volcanic edifice constructed over several cycles and has a NNE-SSW elongated shape. The cone is surrounded by a large plain formed by debris from flank collapse and lahar deposits.
A series of very explosive (Plinian) eruptions occurred at Ruapehu between about 22,600 and 10,000 years ago. Since then, only one vent has probably been active, Crater Lake in the summit region. Activity in historic time consisted of mild explosive phreatic and phreatomagmatic eruptions often accompanied by lahars threatening the popular ski area on the volcano as well as structures in the surrounding valleys.
On 24th December 1953, a tephra dam holding in the crater lake failed passively, hence the lake drained to produce a catastrophic lahar that destroyed a rail bridge 42 km from the volcano, just as the Wellington-Auckland passenger train was crossing and fell into the valley, causing 151 fatalities.
See also: Sentinel hub | Landsat 8 | NASA FIRMS