Jan 6 2010 - Volcanic activity in New Zealand 2009
2009 was another quiet year for New Zealand's volcanoes with no eruptions onshore, but several short-lived periods of activity were recorded from Monowai submarine volcano in the Kermadec Islands.
Aerial view of the discoloured sea above Monowai submarine volcano, 27 October 2009 (photo courtesy RNZAF).
Monowai submarine volcano lies about 1450 km north-north-east of Auckland (380 km north of Raoul Island) in the northern Kermadec Islands, and the summit of the active cone ranges between about 70 m and 130 m depth. Activity has often been observed or recorded in the last 30 years. During 2009 activity was noted in early and mid-May, early July, mid-September, late October, mid-November, late November to early December and mid-December based on seismic data recorded in Rarotonga, Cook Islands. On 28 October the RNZAF overflew the area and confirmed the activity, observing discoloured sea water related to suspended sediment and precipitates (see accompanying picture).
White Island's crater lake, which began to re-form late in 2007 after nearly emptying itself earlier that year, rose to about 8 metres below overflow in 2009 and stabilised. Minor fluctuations in the lake level, together with small changes in temperature and sometimes colour, are common. These reflect changes in the amount of volcanic steam and gases entering the lake and, to a much lesser extent, variations in rainfall. Changes continued in an area of high temperature (100 - 120 °C) steam vents on the southern side of the main crater floor; these vents have been changing slowly for some years. In May they became more active and produced small amounts of mud spatter and unpleasant acid emissions during the rest of 2009. The sulphur dioxide and carbon dioxide gas flux varied within typical levels during the year. Although there were minor changes in surface activity White Island remained at Volcanic Alert Level 1 throughout 2009.
Ruapehu experienced a period of elevated lake temperature (33 - 36 °C), slightly elevated sulphur dioxide and carbon dioxide gas emission, and volcanic tremor in January. The lake temperature then declined to reach a low of 18 °C by May before starting to re-heat in June. Volcanic earthquakes on 14 July produced a small overflow from the lake but no eruptions. The lake temperature rose to around 30 °C in September but had slowly declined to 21 °C by year end. Ruapehu remained at Volcanic Alert Level 1 throughout 2009.
In May 2006 Ngauruhoe began experiencing elevated seismic activity and the Volcanic Alert Level was raised to Level 1. During the second half of 2008 the seismic activity declined and the Volcanic Alert Level was lowered to Level 0 in December 2008. Earthquake activity recommenced in late December 2008 and continued until June 2009, but at a declining rate through that time. As the earthquake activity in 2009 was less than that observed in 2007 - 2008 and as there was no other responses from the volcano, the Volcanic Alert Level remained at Level 0.
Over the last few years continuous GPS (Global Positioning System) monitoring equipment has been installed around Taupo, Rotorua and Okataina calderas to record ground deformation and complement the seismic and lake levelling measurements. Small scale changes (up to several millimetres) have been recorded around both Okataina and Taupo. These are probably quite common, but have only been seen with recent improvements in monitoring.
Activity during 2009 at other volcanic centres included seven small earthquakes located near the Auckland Volcanic Field and ten within the National Park at Taranaki (Egmont).
