As well as the challenging weather conditions that cause severe icing of equipment on Ruapehu, RAL has had to learn to deal with the effects of volcanic activity on this active volcano. Lift queues and cafes have been moved away from lahar paths and a sophisticated early warning system now operates on Ruapehu which should give visitors to the ski areas time to get out of the valleys and move to higher ground.

1945

Between August and November frequent volcanic eruptions take place from the empty active crater of Ruapehu. Heavy ash showers disrupt skiing and the Chateau's water supply leading to the hasty evacuation the the psychiatric patients who had been occupying the Chateau at the time.

1953

During the 1945 eruption a dam of unstable ice, volcanic rubble and ash was formed around the Crater Lake. With the mountain now quiet, this potential daner went unmonitored. On Christmas Eve 1953 the dam collapsed, sending a large lahar down the Whangaehu River. The lahar smashed into the main trunk railway bridge at Tangiwai, causing it to partially collapse. Despite some forewarning from a passing driver who had noticed the bridge under water, the passenger express train from Wellington was unable to stop in time, resulting in one of New Zealand's biggest ever disasters - 151 lives lost.

1969

An eruption occurred from the active crater of Ruapehu, destroying Dome Shelter and expelling a large volume of water from the lake. Volcanic mudflows (lahars) cascaded down several major valleys. One lahar swept through the Whakapapa Ski Area and destroyed the kiosk near the Staircase T-Bar which lay in its path. No one was hurt as the mudflow occurred at night.

1971

A party surveying the crater rim saw the lake surface bulge, then burst skyward. Two of the men were drenched with acid water, blasted by choking ash and toxic gas and bombarded with rocks.

1975

Eruptions sent lahars down the Whangaehu River and through teh Whakapapa Ski Field. A lahar washed out the drive station of No.2 charilift.

1995

At around 5pm on 23 September, following a series of small eruptions earlier that week, the mountain burst into life blasting lake water, steam and ash into the sky as skiers made their last run down the mountain. A series of explosions followed over the next two days sending half the water from the Crater Lake down the Whangaehu River and a 10km-high plume of ash into the air.

Skiers quickly returned to the slopes only to find on 7 October that the mountain wasn't done. The season ended early, with volcanic activity dropping off by mid-November.

1996

 In June 1996, as staff arrived in the area for their first induction and training, Ruapehu again showed its strength blasting out plumes of ash, blocks of hot rock and lava bombs. On 20 July fountains of hot lava were seen and sonic booms shook the area. An 11km-high cloud dispersed ash as far as Opotiki and it wasn't until September that the mountain was quiet again.

2007

On 18 March the unstable tephra dam that formed on the rim of the Crater Lake during the 1995/96 eruptions gave way, sending a lahar down the Whangaehu River. The lahar and the route that it took were long predicted and prepared for, with early warning systems in place to close affected roads.

Then on 25 September around 8pm a small eruption caused a lahar flow from the Crater Lake, through Dome Shelter and down the valley alongside the Far West T-Bar at Whakapapa. As it travelled through Dome Shelter the lahar trapped sleeping tramper, William Pike, who survived but later lost his leg. It also narrowly missed Whakapapa trails manager, Shane Buckingham, as he worked the night shift grooming trails off the Far West T-Bar. Shane saw the lahar coming, manoeuvred his snow groomer out of the lahar path just in time and later helped with Mr Pike's rescue.