Declining earthquake activity at Mt. Ngauruhoe has caused GNS Science to reduce the volcano’s alert status.
In a bulletin issued yesterday, Friday the 5th of December 2008, GNS Science announced that the number of earthquakes recorded near Mt. Ngauruhoe has returned to normal since the middle of this year.
The increased activity began in May 2006 when the number and magnitude of low frequency earthquakes near the volcano increased significantly. During the early part of June 2006 earthquake counts reached 50 per day; the largest events being approximately magnitude 1, at a depth between 1 and 4 km, located slightly north-east of the summit. By the middle of the month, rates had dropped to 10-20 events per day.
Over the following two years, scientists recorded between 5 and 30 earthquakes per day, with activity peaking at about 80 events per day in January of this year.
Volcanologists increased their surveillance of Mt. Ngauruhoe, which last erupted strongly on the 19th of February 1975. A regular programme of volcanic gas and temperature measurements was also instituted, revealing only small amounts of volcanic gases and no temperature changes in the main steam vent at the summit which typically measures 86 ºC.
It is now thought that the increased earthquake activity was related to geothermal rather than volcanic activity.
Mt Ngauruhoe is now at Alert Level 0 (typical background activity).
[Compiled from data provided by the GeoNet project and its sponsors EQC, GNS Science and FRST.]