Since mid-2008 the number of volcanic earthquakes close to Ngauruhoe has declined to the background level. Regular measurements of volcanic gas levels and the temperature of a summit gas vent have failed to record any significant changes over the last two and a half years.

“The reduction in earthquake activity means that an eruption in the near future is unlikely without further earthquakes or other changes and the appropriate alert level is therefore zero”, said GNS Science Volcano Section Manager Gill Jolly.

A significant increase in earthquake activity in May 2006 prompted the alert level to be raised to one (signs of volcano unrest). Over the next two years GeoNet recorded an average of 5 to 30 earthquakes a day close to Ngauruhoe, though the maximum daily number was as high as 80. “Since mid-2008 the number of earthquakes has returned to a typical level of a few per week”, said Brad Scott, GNS Science Volcano Surveillance Coordinator. “This no longer constitutes significant unrest”, he said.

The regular programme of gas and temperature measurements at Ngauruhoe was boosted as a result of the earthquakes starting in May 2006. However, these measurements have consistently shown only small amounts of volcanic gases (sulphur dioxide and carbon dioxide) and no changes in the temperature of the one notable steam vent in the summit area (typically about 86°C).

GNS Science Volcano Seismologist Art Jolly said, “The earthquake data we collected during the unrest probably points to a geothermal rather than volcanic source for the events, and we hope it will help us better understand the next unrest episode at Ngauruhoe”.

“Although the unrest that started in May 2006 hasn’t resulted in an eruption, raising the alert level was consistent with the observed activity. It emphasised that Ngauruhoe remains an active volcano and everyone needs to be aware of this” said Brad Scott.

Alert Status

Ngauruhoe is no longer showing signs of any significant unrest and the Volcanic Alert Level has been reduced to Level 0

Steven Sherburn
Duty Volcanologist