As a result of a new research project measuring the temperature and level of the lake we observed a 15 cm jump in lake level following the volcanic earthquake. The crater lake temperature is unchanged at 20 °C.

The crater lake was examined by helicopter late Tuesday morning. Viewing conditions were very poor, but no obvious changes have occurred since the last visit on July 2. No eruption had occurred and the lake was overflowing.

Our preliminary interpretation is that the volcanic earthquake was followed by about 20 million litres (about 8 Olympic-sized swimming pools) of extra water moving into the lake from the hydrothermal system beneath it. A much larger rise in lake level followed a very small eruption in October 2006, so such phenomena are not unknown at Ruapehu. However, this is the first time we have been able to correlate such a small rise with a single volcanic earthquake.

Observations will continue as conditions allow.

The Volcanic Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest).

Steven Sherburn
Duty Volcanologist

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.

Steven Sherburn
Duty Volcanologist

Many new springs are forming on the Main Crater floor, and older springs are starting to flow again. These changes are similar to those observed during the previous lake filling (2004 - 2006). The Crater Lake temperature remains hot at 57 °C and the lake colour has also changed to a light green, reflecting little suspended sediment.

On the south side of the Main Crater floor, about half way between the lake and the sea, is an area of high temperature (101 - 103 °C) fumaroles. Steam, gas and mud emissions creating acid rain have increased from the largest vent in the last couple of weeks, and this will continue as the lake rises. Fumarole activity in this area has been increasing for several years. Activity has fluctuated in these features and they have varied between being ‘wet’ and ‘dry’ dependent on the water level in the Crater Lake.

Other monitoring, including the deformation surveys and soil gas mapping, have also shown changes about this fumarole area as it has heated and increased in activity. The current changes represent changes in the shallow geothermal system related to the rising water levels on the island.

White Island’s Crater Lake occupies a crater that formed during eruptions in the 1970s – 1990s. The last eruption at White Island, in 2000, occurred from a vent that is now beneath the lake.

No other significant changes have been observed at White Island.

The Volcanic Alert Level for White Island remains at Level 1; there is no significant change in volcanic activity on the island.

Steven Sherburn
Duty Volcanologist

Ongoing monitoring at Ruapehu, including a recent Crater Lake visit to measure the lake temperature and collect water samples, data from airborne gas measurements and seismic activity, have shown changes in the last month. These changes indicate that the period of lake cooling and lower gas flux is over.

The Crater Lake temperature has now increased to 22 °C, up from 16 °C in August. This temperature change was accompanied by some volcanic tremor. From October 2007 to June 2008 the lake temperature ranged between 34 to 37 °C before declining to a low of 16 °C in August 2008. The airborne gas plume measurements have shown a similar trend with SO₂ and CO₂ gas emissions being high while the lake was hot, decreasing when the lake cooled and now increasing again. Cyclic activity in the Crater Lake is very common at Ruapehu.

These observations are consistent with the volcano-hydrothermal system now being more open to the Crater Lake. This type of volcano unrest should result in the lake temperature continuing to rise and the lake colour changing as sediments on the lake floor are disturbed by the increased gas flow into the lake. Ruapehu remains an active volcano and future eruptions may occur without warning.

The Volcanic Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest).

Brad Scott
Volcano Surveillance Co-ordinator

Ongoing monitoring at Ruapehu, including a Crater Lake visit to measure the lake temperature and collect water samples, data from airborne gas measurements and seismic activity, have shown declines in the recent measurements. This indicates that the current period of elevated unrest is passing.

The Crater Lake temperature has now dropped to around 23 to 25 °C, having ranged from 34 to 37 °C since October 2007. The latest measurement was 23.3 °C (July 15). The airborne gas plume measurements which had shown significant increases after April 2008 now show that SO₂ and CO₂ gas emissions have decreased to the typical background levels for Ruapehu.

Results from the Crater Lake chemistry are also indicative of cooling in the vent area. The slight increase in the level of volcanic tremor we previously reported has also declined to typical background levels.

These observations are consistent with the volcano-hydrothermal system now cooling. The current phase of volcano unrest appears to be over, however Ruapehu remains an active volcano. Future eruptions may occur without warning.

The Volcanic Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest).

Brad Scott
Volcano Surveillance Co-ordinator

* Previously known as Science Alert Bulletin and Scientific Alert Level.

Ongoing monitoring at Ruapehu, including a Crater Lake visit to measure the lake temperature and collect water samples, data from airborne gas measurements and seismic activity have continued to show variations.

The airborne gas plume measurements show the SO₂ emission has gradually increased since last year’s eruption and the CO₂ flux has varied. The emission rates of both SO₂ and CO₂ gases have shown significant increases since April 2008, being about ten times above the typical background. Our latest measurements on June 12 remains high.

The Crater Lake temperature has remained elevated and fluctuates between 34 and 37 °C. The latest measurement was 35.2 °C (June 12). Sustained heat from depth is required to keep the temperature this high for this length of time. It is believed that the source of this heat is magma within the volcano conduit. This magma is also producing the higher than normal gas flow and other chemical changes in the lake.

The slight increase in the background level of volcanic tremor we previously reported has now declined to typical background levels.

These observations remain consistent with the volcano-hydrothermal system responding to recent eruptions and ongoing interaction with magma in the volcano conduit. The volcano remains in a state of unrest and the possibility of further activity remains at the volcano. If further eruptions occur, they may occur without warning.

The Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest) and will continue to be re-assessed regularly.

Brad Scott
Volcano Surveillance Co-ordinator

The earthquake on Friday has been followed by many aftershocks (several hundreds) and the larger ones have been felt on the Bay of Plenty coast. Monitoring of the volcano since Friday has established that there has been no immediate significant response from the volcano. Starting Sunday morning, and lasting through to Monday we have recorded volcanic tremor and some volcanic earthquakes; these continue intermittently. Volcanic seismicity, including weak volcanic tremor and volcanic earthquakes, are common at White Island. Gas monitoring has not shown any change in gas flux.

White Island is an active volcano and eruptions can occur at any time without warning. As a consequence of this earthquake sequence the eruption hazard at the island may have increased above the normal levels. However as we have not recorded any significant changes over the last few days, it would appear the volcano is returning to a normal quiescent state. Normal cautions should be applied when visiting the volcano.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Brad Scott
for Duty Volcanologist

This morning's earthquake was a tectonic-type earthquake, and these are common in the outer Bay of Plenty. We are recording many aftershocks following this event. The level of ground shaking may have produced some landslides, but we are not aware of any at this time from viewing the camera images. There has been no immediate response from the volcano though the large number of aftershocks means that any seismic response may be difficult to see for several hours.

We will continue to monitor the earthquake activity and, conditions permitting, make a monitoring flight to assess the volcanic gas output. If the volcano responds there is likely to be an increase in gas output and/or an increase in volcano seismic activity.

White Island is an active volcano and there is always a level of hazard associated with it. Moderate-sized tectonic earthquakes are also common events in the outer Bay of Plenty and historically no connection has been demonstrated between them. However as a consequence of this earthquake the eruption hazard at the island may have increased above the normal levels and we would recommend no visits to the island for the next 48 - 72 hours as a precautionary measure.

The active crater at White Island is now occupied by a crater lake, ponding in the crater that formed during eruptions in the 1970s – 1990s. The last eruption at White Island, in 2000, occurred from a vent that is now beneath the lake. Recent volcanic seismicity has included weak volcanic tremor and low frequency volcanic earthquakes, both of which are common at White Island.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Brad Scott
Duty Volcanologist

Data from the airborne gas measurements, seismic activity and Crater Lake temperature have continued to show variations since the September 25 2007 eruption.

The airborne gas plume measurements show the SO₂ flux has gradually increased since last year’s eruption and the CO₂ flux has varied. However the fluxes of both SO₂ and CO₂ gases have shown significant increases in our latest measurements (April 4 and May 7), being about ten times above the typical background.

The Crater Lake temperature has remained elevated and fluctuates between 34 and 36.8 °C. The latest measurement was 34.4 °C (April 26). Sustained heat from depth is required to keep the temperature this high for this length of time. It is believed that the source of this heat is magma within the volcano conduit. This magma is also producing the higher than normal gas flow and chemical changes.

The slight increase in the background level of volcanic tremor has continued, as have some short periods of stronger volcanic tremor. However volcanic tremor and changes in the level of tremor are very common at Ruapehu.

These observations are consistent with the volcano-hydrothermal system responding to recent eruptions and ongoing interaction with magma in the volcano conduit. The volcano remains in a status of unrest and the possibility of further activity remains at the volcano. If further eruptions occur, they may occur without warning. GNS Science will be making further observations this week.

The Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest) and will continue to be re-assessed regularly.

Brad Scott
Volcano Surveillance Co-ordinator

Data from the Crater Lake sampling, seismic activity and airborne gas measurements have continued to show a change since the September 25 eruption.

The airborne gas plume measurements show the SO₂ flux has increased since last year’s eruption. CO₂ flux has varied, but has shown increases recently, while H₂S gas has become measurable since March 2008.

The lake chemistry shows increased Mg/Cl ratios since the September eruption, with variable sulphate and relatively constant chloride concentrations. Chemical equilibrium relationships amongst gases discharging from the volcano suggest that temperatures are increasing in the hydrothermal system at depth.

The Crater Lake temperature rose in response to the eruption by about 20 °C and reached a peak of 37.5 °C by December 21 2007. Since then it has remained elevated and fluctuated between 34 and 36.8 °C. Sustained heat is required to keep the temperature this high for this length of time. It is believed that the source of this heat is the magma that is producing the higher than normal gas flow and chemical changes.

There has been a small increase in the background level of volcanic tremor and some short periods of stronger volcanic tremor. However volcanic tremor and changes in the level of tremor are very common at Ruapehu.

Since September 2007 magma has started to degas more than is normal at Ruapehu and this is carrying with it additional heat which is keeping the temperature of Crater Lake hot. It is not clear if these changes are signs that further eruptions will occur. If further eruptions do occur, they may occur without any warning.

The Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest) and will continue to be re-assessed regularly.

Brad Scott
Volcano Surveillance Co-ordinator

Accompanying the rise in lake level has been a drop in lake temperature from 63 °C to 53 °C, which reflects the lake’s greater volume. The lake colour has also changed from a turbid grey to a light green, reflecting less suspended sediment.

Fluctuations in the level of the lake at White Island, together with its temperature and sometimes colour, are common and reflect several factors including changes in the volcanic steam and gases entering the lake and variations in rainfall.

White Island’s crater lake occupies a crater that formed during eruptions in the 1970s – 1990s. The last eruption at White Island, in 2000, occurred from a vent that is now beneath the lake.

No other significant changes have been observed at the White Island and normal monitoring, including the lake level, is continuing unchanged.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Steven Sherburn
Duty Volcanologist

The Volcanic Alert Level remains at Level 1 (some signs of unrest).

Since our last update (1 November 2006) elevated volcanic earthquake activity has continued at Ngauruhoe. The number of events per day has typically ranged between 5 and 30 earthquakes per day. This activity started in late May 2006 and the largest earthquakes are about magnitude 1.5. Observations suggest that the earthquakes continue to occur within about 1 km of the surface beneath the volcano's northern flank.On January 6 the number of events started to increase and by 9 - 10 January there were up to 80 per day, decreasing slightly since then. The magnitudes of the larger events ranged between M 1.2 and 1.5.

In response to these changes we have visited the volcano. Measurements of volcanic gas concentrations, temperatures and soil gas flux were made at the summit area of Ngauruhoe on 17 January. These data have not changed since the unrest began in late May 2006, and are similar to measurements made in 2006 - 7. The maximum fumarole temperature near the summit remains about 86 °C.

We have also installed 3 portable seismographs to collect more data on the continuing earthquakes.

We have recorded no other signs of unrest at Ngauruhoe, and have no evidence that an eruption is imminent. We will continue to monitor as necessary.

Brad Scott
Duty Volcanologist