Jan 19 2012 - Volcanic activity in New Zealand 2011

During 2011 the extensive surveillance programme undertaken by GeoNet continued on New Zealand’s active volcanoes.

The Crater Lake at Ruapehu cycled through two heating episodes during the year, with a sustained cool period from July to October. The first heating cycle peaked in late February when the lake temperature reached 41 °C. During the second cycle in October-December the temperature reached 37 °C. No eruptive activity was observed during the year. Although activity has been low, gas flux has continued to vary during the year, carbon dioxide (CO₂) ranging from 233 to 2075 tons per day, sulphur dioxide (SO₂) from 4 to 34 tons per day and hydrogen sulphide (H₂S) from 6 to 42 tons per day. Volcanic gas odour was often reported during the second heating episode. Volcanic earthquake activity remained at low levels, as did volcanic tremor except for a deep volcanic earthquake in November with very long period waves. Ruapehu remained at Volcanic Alert Level 1 throughout 2011.

The surveillance programme for White Island includes gas and water sampling, ground deformation, soil gas surveys, seismic monitoring, web cameras and equipment servicing. During the year the Crater Lake water level has fallen to about 16 metres below the overflow, as the temperature rose to over 66 °C. Minor changes have been observed in an area of high temperature (118 - 200 °C) steam vents on the southern side of the Main Crater floor. These vents have been changing slowly for some years. The gas flux (measured from the air, from soil gas surveys and from the miniDOAS spectrometer) has remained low for White Island. CO₂ has ranged from 928 to 1930 tons per day, while SO₂ has ranged from 88 to 237 tons per day. The deformation survey confirmed that uplift which has been recorded during the last 2 to 3 years has stopped. Volcano seismicity remained around typical background levels. The Volcanic Alert Level remained at Level 1 during the year.

In early 2006, small low-frequency volcanic earthquakes became present at Ngauruhoe. The level of seismicity has fluctuated over 2011 with very low levels of activity during the year. The Volcanic Alert Level remained at Level 0 during 2011.

Monitoring at Raoul Island has continued, with no anomalous trends having been observed in the temperatures or water levels of the Crater Lakes. The Volcanic Alert Level remains at Level 0.

Anomalous temperatures were reported from the hot pools on Mokoia Island (Rotorua) and water samples were collected. The results show no changes from previous sampling.

We continued to see evidence on the Rarotonga seismic record of small-scale eruptive activity at Monowai seamount. Activity was confirmed by surface observations in June and August.

Small earthquakes have continued to occur in the Taupo Volcanic Zone, particularly offshore of Matata, south-west of Kawerau and at Waimangu, and along the Haroharo vent lineation within the Okataina Volcanic Centre. Not so many events have been located within Taupo Volcano, but activity continues to the south-west of the lake through Turangi to Lake Rotoaira. Events have also been recorded on the northern parts of Tongariro and around Ruapehu, in particular to the west of the volcano. No events have been recorded under Taranaki, but seismic activity continues to the west of the volcano.