AN ESTIMATED 1?34?million cubic metres of volcanic mud, rock and water swept down the Whangaehu River valley on the morning of March 18, bringing peak river levels to 6?5?m at the Tangiwai Bridge, infamous as scene of New Zealand’s worst railway disaster.The ’lahar’ was caused when the rim of Mount Ruapehu’s active volcanic crater gave way, sending the lake held behind it crashing down the mountain side. New Zealand’s railways have been aware of the potential destructive power of lahars since December 24 1953, when a lahar destroyed the previous Tangiwai Bridge. Postal clerk Cyril Ellis desperately attempted to alert the crew of the oncoming train, but the Wellington - Auckland night service plunged into the swollen river just after 22.00, killing 151 of the 285 people on board.March 18’s lahar was estimated to be around 25% larger than the one in 1953, but this time warning sensors installed eight years ago provided infrastructure manager Ontrack with enough warning to stop two passenger trains. The bridge was inspected that afternoon, and services resumed the next day. Thanks to the preparations made, the biggest safety risk was posed by sightseers coming to view the aftermath.n