Lahar on Mt Ruapehu

The forecast lahar from Mt Ruapehu’s crater lake flowed down the mountainside late this morning.

Since the 1995 and 1996 eruptions, the crater lake on the volcano has risen behind a weak tephra dam which accumulated to a depth of 6-7 metres on the usual outlet on the south-eastern rim of the crater.

Lahar monitoring alarms were triggered at 10:47 this morning, Sunday 18th March 2007 NZST when the tephra dam collapsed and released the lake contents in a lahar down the mountainside. The dam had been leaking since early January.

The Civil Defence emergency plan was activated, closing roads near the volcano and State Highway 1.

Despite steady rain in the area in the last 24 hours, rivers are not affected by an added burden of water which may limit the effects of the mudflow. However, it will take some hours for the lahar to complete its passage down the Whangaehu River, at which time the extent of the flow and any damage it caused will be known.

The seismic station at Far West T-Bar showed an increase in trace at 11:24 this morning, against a background of noisy signal caused by weather conditions on the mountain. This may have been caused by vibrations detected by the station as the lahar debris flowed past.

As luck would have it, low cloud is obscuring the view of the volcano from the webcam located at Chateau Airport. Scientists are monitoring the event from a helicopter, but may also be hampered by the cloud in the area.

Leave a Reply