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Mt Tongariro - Source: Wikimedia Commons
A series of quakes beneath Mt Tongariro have resulted in the
alert level for the volcano being raised.
GeoNet said typically Tongariro experienced two such quakes -
magnitude 2.5 or less - a year but there had been more than 20
since July 13.
It said the sequence started on July 13 and declined for a period,
before restarting on July 18 and increasing in number
yesterday.
''These indicate unrest at Tongariro and give reason to change the
Volcanic Alert Level to level 1 [from 0] and the aviation colour
code to yellow [from green].''
''These earthquakes are small (magnitudes <2.5) and have only
been well recorded by a few of the seismometers in our permanent
network. The earthquakes cluster in a zone between Emerald Crater
and the Te Mari craters at 2-7km depth.
GeoNet said to better understand the significance of the quakes it
was planning to deploy portable seismic recorders around the
epicentres and conduct sampling of selected hot springs, crater
lakes and fumaroles in the area.
Mt Tongariro is a volcanic complex that lies to the north of
Ngauruhoe. It consists of numerous craters and vents.
The Te Mari craters lie about two kilometres east of Ketetahi hot
springs on the north side of Mt Tongariro. The Te Mari craters are
the last craters to be active on Tongariro. Ash eruptions have been
recorded from Tongariro from 1855 to 1897, as well as unconfirmed
activity in 1926-27.