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Observations over the weekend suggest no further sustained ash emissions have occurred from the active vents. Occasionally images on the web camera indicate very minor amounts of ash may be present in the steam plumes, but this has not been confirmed. Such intermittent appearance of ash is likely due to shedding of debris on the fumarole walls and may be expected to continue. The seismic and acoustic activity remains low, and the gas flux from the island has not changed substantially during this minor activity.
Although Tuesday’s eruption has ceased, White Island is always capable of a new eruption at any time, without prior warning. GeoNet continues to monitor the volcano for possible renewed activity.
phone 07 3748211
Analysis of ash collected on Wednesday shows no evidence that Tuesday’s eruption was driven by new magma. Instead, gas flow dragged recently loosened material to the surface. Seismic and acoustic activity at remains low, and the gas flux from the island has not changed substantially since before Tuesday’s eruption.
Although Tuesday’s eruption has ceased, White Island is always capable of a new eruption at any time, without prior warning.
GNS Science continues to closely monitor White Island and our other active volcanoes through the GeoNet project. The Volcanic Alert Level ranges from 0 to 5 and defines the current status at a volcano. Aviation Colour Codes are based on four colours and are intended for reference only in the international civil aviation community.
phone 07 3748211
VOLCANIC ALERT BULLETIN: WI – 2016/10
11:15 Wednesday 14 September 2016
Volcanic Alert Level 3 (no change)
Aviation Colour Code: Orange (no change)
The level of volcanic activity seen yesterday and overnight is very minor, with small amounts of volcanic ash being passively emitted from vent(s) within the active crater. We have reviewed all available data sets; seismic activity remains low, the gas flux remains low and there are no measureable acoustic signals. Some of our cameras are still affected by ash and steam, hence limiting our observations.
The poor light conditions and local high cloud make it difficult to assess the amount of ash present. It does appear the bulk of the emission was yesterday and only minor amounts are now present. Should ash emission increase today there is a low possibility of traces of ash reaching the East Cape area (based on weather and ashfall models).
The current activity is minor. We will review the situation if changes occur. Implications for visitor safety remain unclear. The Volcanic Alert Level remains at Level 3.
VOLCANIC ALERT BULLETIN: WI – 2016/09
15:15 Tuesday 13 September 2016
Volcanic Alert Level 3 (no change)
Aviation Colour Code: Orange (no change)
As far we can tell from our monitoring data there has been no escalation in the level of activity at White Island since late morning. Seismic activity remains low on the island. Some of our cameras are now been affected by ash and steam, so we may not see much from them in the short term.
The level of volcanic activity seen earlier today was very minor, with volcanic ash been passively emitted from a vent on the 2012 lava dome.
The ash is visible on a NZ Metservice visible satellite image, which shows a plume extending offshore of East Cape. Any ash fall will follow wind direction and is likely to be blown offshore over the next day.
The current activity is minor. We will review the situation in the morning unless changes occur overnight. Implications for visitor safety remain unclear.
VOLCANIC ALERT BULLETIN: WI – 2016/08
12:50 pm Tuesday 13 September 2016
Volcanic Alert Level 3 (change from Level 1)
Aviation Colour Code: Orange (change from Green)
The level of volcanic activity at White Island has increased late this morning with minor volcanic ash been passively emitted from a vent on the 2012 lava dome. A report from the island at 11.50 h has confirmed the ash emission.
The Volcanic Alert Level is now raised to Level 3, from Level 1.
The Aviation Colour Code is changed from Green to Orange.
The current activity is minor. We are unsure of the implications for visitor safety and will be issuing a further VAB later this afternoon (3 pm).
GNS staff visited White Island (Whakaari) last week to continue their routine monitoring of the volcano and complete reinstating the levelling and magnetic networks. We also collected thermal IR images of the lava dome area, measured the Crater Lake level and temperature and fumarole temperatures. The Volcanic Alert Level remains at Level 1 (typical background levels).
Observations during this visit confirm the Crater Lake is reforming and growing. The April 27 eruption removed about 13-15 m of lake floor sediments and the new lake is forming at a lower level on the floor of the crater. The lake is currently about 28.4 m below the overflow level. Since 19 May the water level has risen about 3 m and the lake temperature has decreased as it gets larger. The temperature is now 52 ºC. The lake is now a light lime green colour, having changed from a milky grey shortly after the April eruption.
We are sometimes able to get Thermal IR images of a rocky lava mound in the back of the 1978/90 Crater and have established information on the very high temperatures that are present there. This is the same area where a lava dome grew in 2012. There are two areas of hot gas output and the temperature measurements ranged from 198 to 295 ºC. These are down on the measurements we made in August when they ranged 292 to 337 ºC in the hottest area. The temperature of Fumarole 0 (the largest accessible one) has changed little. We measured 170-173 ºC this time and 168-171 ºC last visit.
As we reported in May and June many of our survey pegs were sheared off or broken by the April eruption. This has had implications for the regular surveys we do like the levelling, magnetics and soil gas flux. We have completed reinstalling pegs and made the first magnetic and levelling surveys last week. Minor volcanic unrest continues.
The active vent-crater at Mt Ruapehu is occupied by a crater lake. Recently the lake has been cooling and we even discussed the possibility of new record low temperatures. The Crater Lake displays temperatures that typically range between about 15 and 40 °C. The lake has cooled to a minimum of 12 °C (15 August) but has now started to heat rapidly. GeoNet obtains temperatures from the lake using a data logger with a temperature sensor in the lake and communications via a satellite link.
In early August we discussed the possibility of the post 1995/1996 Crater Lake reaching a new low temperature as the lake was cooling strongly at that time. The lake reached a new minimum temperature of 12.0 °C on 15 August. For much of August the lake temperature ranged 13-14 °C, occasionally looking like it maybe going to turn and start heating. The temperature was starting to rise, very slowly, in late-August, but with quite a bit a lot of variability. However by 2 September a rising trend was clearly established. The lake temperature is now 17.6 °C.
On May 11 2016 the lake reached a high of 46°C, the highest we have observed since it reformed in 1999-2000. This high temperature was also accompanied by volcanic tremor and an increase in the output of volcanic gas. The Volcanic Alert Level (VAL) was raised to Level 2 at that time, lowering to Level 1 in early July when the gas output and volcanic tremor levels declined. About 2 days after the lake temperature stared to rise on 2 September, the level of volcanic tremor also started to rise and has remained present since 4 September. The heating and cooling cycles are controlled by a mix of volcano and geothermal processes. Further sampling and visits to the Crater Lake are planned as the weather allows, being part of the standard GeoNet monitoring programme for Mt Ruapehu.
The workshop was structured around several modules that walked along the pathway outlined for the day. We started looking at various recent examples of eruptions that have produced significant ballistic falls in Japan and New Zealand. The group then compared and contrasted the hazard and risk environments at New Zealand volcanoes that have or could produce ballistics. We looked at Te Maari, White Island, Ruapehu and Auckland. The next item was based on ballistic hazard maps and display of intensity information. The module explored the way and types of information we could put on maps. Do we show risk or hazard or intensity metrics? Do we look at long-term and background situations versus crisis ones. How can we consolidate all these needs and products?
This lead to a session looking at how we collect data about the deposits, what are the key variables we should look for to collect quality data. What were some of the lessons from recent eruptions? What are the data gaps and limitations and how do we address this. Based on this the workshop looked at how we can create numerical models from these data and the parameters we need to know. The participants then got to use a model (Ballista) to see what the effect was on changing input parameters (direction, elevation, velocity etc.). Will a fridge sized block go as far as a baseball sized one? Now that we knew were the blocks would go it was time to look at the exposure and vulnerability of things in the way. This included infrastructure and people. The results from Canterbury Universities cannon experiments were one of the highlights of the day. How much damage does a block tossed from a volcano do a couple of kilometres away!
This week we have established a new target on the crater rim, so we can start following the water level changes in the new lake, which is now forming on the crater floor. The Crater Lake(s) at White Island have had quite a history of change since the first major lake started to form in 2003. From mid-2003 to early 2006 the water level rose about 26 metres, getting to within 2 meters of overflow. The lake then fell to be about 23 meters lower by mid-2007. During this time the lake was heating, so it was basically being evaporated away. It refilled to about 7 metres below overflow by early 2009 and stayed there until heating started in late 2010. The lake again evaporated away. Small eruptions followed in August and October 2013.
The lake started to reform in November 2013. From December 2013 to May 2014 the lake rose about 3 metres and then remained unchanged until June 2015. Then the water level rose another 2 metres before again starting to evaporate away in March 2016, falling over 2 metres before the 27 April eruption. Conditions are now stable enough for us to start monitoring the water level again via the web camera images. The Crater Lake temperature is now 60 °C and the water level about 31 m below overflow.
The volcanic alert level for Mt Ruapehu remains at Volcanic Alert Level 1 (minor volcanic unrest). The Aviation Colour Code also remains unchanged at Green.
The gas flight completed on August 10 recorded the volcanic gas at levels typical of low-background output for Mt Ruapehu. Convection was noted in the lake. On August 11 a Crater Lake sampling for gas and water was also completed. Up welling was again obvious in the lake and was outlined by sulphur slicks, which are frequently seen when the lake is convecting. The lake was a dark green-grey colour and was overflowing. There was a fairly strong sulphur smell near the lake. The lake temperature was measured at 12.6 ºC, consistent with the data logger observations. Today the data logger reports a temperature of 12.9 ºC.
The level of volcanic tremor which was elevated to moderate levels in May-June has declined and is now at typical background levels. Data available at present indicates the level of volcanic unrest at Mt Ruapehu is low.
GNS Science continues to closely monitor Mt Ruapehu and our other active volcanoes through the GeoNet project. The Volcanic Alert Level ranges from 0 to 5 and defines the current status at a volcano. Aviation Colour Codes are based on four colours and are intended for reference only in the international civil aviation community.
Phone 07 3748211
The active vent-crater at Mt Ruapehu is occupied by a crater lake. This summit Crater Lake displays temperatures that typically range between about 15 and 40 °C. This has been a common feature of the Crater Lake since the mid 1960’s. The lake took several years to refill and become established following the 1995 and 1996 eruptions. GeoNet obtains temperatures from the lake using a data logger with a temperature sensor in the lake and communications via a satellite link.
Since May the temperature of the Crater Lake has been declining and continues to do so. The lake is now 13.5 °C and has been cooling at about 0.5 °C per day. In August 2014 the temperature was just under 15 °C, the lowest since the 1995/1996 eruptions. Now the lake is cooler by about 1°C. We have measured cooler temperatures more than 10 times in the 1980’s and 90’s. Cool lake temperatures are not that unusual. The heating and cooling cycles are controlled by a mix of volcano and geothermal processes. The heat flow into the volcano from the hot and sometimes molten rock under it just gets turned on and off, like a tap. Then the lake heats or cools and maybe sets a new record.
On 11 May 2016 the lake reached a high of 46°C, the highest we have observed since it reformed in 1999-2000. This high temperature was also accompanied by volcanic tremor and an increase in the output of volcanic gas. The Volcanic Alert Level (VAL) was raised to Level 2 at that time, lowering to Level 1 in early July when the gas output and volcanic tremor levels declined.
During the last 50 or so years Mt Ruapehu has erupted often and one trend we have noticed is that the eruptions occur from a hot lake. However we have also noted a few from a cold lake. They do not occur every time the lake gets hot or cold, however if one does occur it will more likely be at one of these extremes. This becomes a time when we pay some extra attention to the status of the volcano. Further sampling and visits to the Crater Lake are planned as the weather allows, being part of the standard GeoNet monitoring programme for Mt Ruapehu.
In the 15 years since GeoNet started a lot of work has been undertaken on the networks. This has ranged across the sensors, digitizers, communications links, out stations and optimization of the data collection and archive. These have been focused across the whole project with many benefits for the volcanology team. When we started we already had many seismic dots on the map and have had a modest increase in those. However the technology behind the dots has improved so much. Fifteen years ago we had no dots on the map for the GPS, gas and acoustic sensors and remote cameras. Today we have multi-sensor arrays at many of the volcano sites (seismic, GPS, gas and acoustic).
During the 1990s the focus was on creating ‘volcano-seismic networks’ at each of the active volcanic centres, getting the data back to a local data recorder (digitizer). We then couriered the weekly data tapes around for subsequent analysis. The concept of a central data centre was almost non-existent. We deployed a USGS-based technology for converting the sensor signal so we could transmit it across UHF radio links and then record it. All the sensors were what is termed 1-D, in that it recorded only the vertical component of the seismic wave. Some lived down shallow bore holes (10-30 m) to reduce the local noise. Two of the networks were owned and operated by the local Regional Councils (Auckland and Taranaki).
The GeoNet approach was to upgrade all the sensors to 3-D (vertical component plus two horizontal components), install digitizers on site (with backup memory) and use digital communication systems to move the data around. We also added in some new sites to improve cover or create cover where we didn’t have any. This was an enormous step forward in data quality and quantity. This was followed by an evaluation of the data quality, leading to several sites being placed in deep drill holes to improve data quality. Some of the holes are 200-300 m deep, especially in Auckland where there is a lot of ‘cultural noise’ made by the city - and we are interested in the area under the city! All of the volcano sites are now part of the New Zealand network.
In the early 1990s we had started to use GPS receivers in collaboration with international research teams to measure ground deformation on a regional scale around the volcanoes and elsewhere in New Zealand; we didn’t have any permanent sites. With the advent of GeoNet we were able to start creating a GPS network with permanent recorders on or near the volcanoes. We had two goals with our first networks: to record the regional deformation, and that local to the volcano centres. Some of the sites form lines across the volcanic zone, while others focus on the volcano, especially the caldera volcanoes. The volcano sites are also an integral part of the New Zealand-wide network.
When you're unable to see the volcano it’s not so easy to confirm or deny if an eruption has occurred. We often see volcanic earthquakes that do not produce an eruption at the surface. With our changeable New Zealand weather and half the day being night, we don’t get to see them all that often. This is where acoustic sensors come in to play as they record the airwaves from the explosions. So if we have a volcanic earthquake and an airwave, then we can be pretty certain we have an eruption.
Active volcanoes put out lots of volcanic gas, sometimes this can be thousands of tonnes per day (or tens of kg per second). The main gases are water (H2O), carbon dioxide (CO2) and sulphur dioxide (SO2). We have several techniques to measure all of these gases at the volcano, but not so many that can give us continuous data. In fact we can only get SO2 reliably at present. We have these sensors at White Island (Whakaari) and Tongariro, and under suitable conditions get data daily.
Nothing beats getting to see the volcano. Around 2000 we started using Olympus digital cameras as remote cameras. These had a cable that could be connected to your computer and software would trigger the camera and download the photo from the camera. We then nutted out a way to do this remotely, both in Whakatane and at the Chateau, and have them transmit the pictures back to us in Taupo. Today we have thirteen cameras that collect an image every second (but we only bring back one every 10 minutes for the website). The cameras are in fact 2 cameras: a daylight one and a special low-light one for night.
In the 15 years since GeoNet was created many people have worked as a part of the Volcano Team. Several have been with us from the start, others have joined along the way, while other have come and gone. There are a few who date back to volcanology in GNS Science and three that date back to the DSIR (Dept. of Scientific and Industrial Research), which was the forerunner to GNS Science. As you will see many have worked all over the world on many varied volcanoes and have a lot of experience in how to deal with volcano crises. Skills range from building monitoring networks, to geology, geophysics, geodesy, geochemistry, social science and communications.
In July 2001 I was still in primary school and I had no idea what GNS Science was, or what GeoNet would become, I just wanted to be a fireman. Today I'm a Volcanic Operations Technician (equally as awesome), part of a team of technicians that make sure GeoNet's monitoring equipment around New Zealand keeps providing useful information on the state of volcanoes, earthquakes and ground deformation.
In July 2001 I was working for GNS Science in the geothermal lab and already involved in volcanoes and geothermal systems. Today I’m the volcano geochemistry technician for the GeoNet volcano team.
In July 2001 I was working for GNS Science undertaking geothermal and volcano fluid research. This took me to volcanoes and geothermal systems and I was keen on the role gases play. Today I’m the Senior Volcanic Fluids Geochemist for GeoNet.
In July 2001 when GeoNet started I had just finished my first year at university at Caltech in Los Angeles; three months before I had decided to switch my degree from astronomy to geology. A year and a half later I decided to be a volcanologist and went on to complete my masters (University of Bristol) and PhD (University of Oregon). I joined GNS Science in 2012 as a post-doc and became permanent staff in 2014. Today I'm a volcanic hazard and risk modeller, I serve as a GeoNet volcano duty officer, and am committed to doing what I can to minimise the impact of future New Zealand eruptions through monitoring and research.
In July 2001 when GeoNet started I was nearing my first year of PhD in the UK, studying how volcanoes persistently release gas for years without erupting. After working in the eastern Caribbean for 5 years as a volcanologist, I joined GNS Science in May 2009 as a volcano geodesist. Today, I head the Volcanology Department and volcano monitoring team.
In July 2001 when GeoNet started, I had just finished my exams (GCSE's) at high school in the south-west of the UK. After more exams, a couple of degrees and a detour in Italy I arrived at GNS Science in 2013. Today I am an InSAR scientist looking at crustal deformation across New Zealand from space (satellites).
In 2001 I was at the Aso Volcanological Laboratory in Japan (visiting Professor) for a year, comparing our monitoring techniques with theirs. Before going to Japan I was experimenting with the first cell-phone connected strong motion recorders (Etnas), and was working on the first volcano-cams. Today I’m the Senior Volcano Geophysicist in GeoNet and work across many volcano problems.
In 2001 I was still at University in UK and knew nothing of GeoNet. I joined GNS Science in 2007 as an operations technician and work in the GeoNet project looking after the seismic and GPS equipment.
In July 2001 when GeoNet started I was with the University of Leeds (UK) and working at Montserrat Volcano Observatory (West Indies) conducting research on seismicity of Soufriere Hills volcano. Today I’m a Senior Volcano Geophysicist with GNS Science, joined in 2006 and conduct research on volcano seismic and acoustic properties.
In July 2001 when GeoNet started I was in Montserrat, West Indies working at the Volcano Observatory as the Director. I joined GNS Science in 2006 as a physical volcanologist. Today I'm Director of the Natural Hazards Division (and still very interested in what the volcanoes are doing!).
In 2001, I was studying for my MSc degree in Earth Sciences at University of Waikato. I joined GNS Science in 2002 as a Volcanology Technician and today, I am a Volcano Geologist. I study the processes responsible for generating eruptions and the surface effects once the eruption has begun. I am part of the Duty Officer team.
In July 2001 when GeoNet started I was at Free University of Brussels, Belgium doing my PhD on the geochemistry of fluids and CO2 degassing on Indonesia volcanoes (Papandayan and Kelud volcanoes). I joined GNS Science in 2009 as a Volcanic Gas Geochemist. My role at GeoNet is to monitor gas emission from New Zealand volcanoes (White Island, Ruapehu, Ngauruhoe, Tongariro etc.), contribute to the interpretation of the geochemical data and contribute as a duty officer.
In July 2001 I was working in mining and mineral exploration geophysics in Australia. I joined GeoNet in November 2002 as a Volcano Geophysicist and later became the Volcano Network Coordinator. In this role I oversaw the modernisation and expansion of New Zealand's volcano monitoring infrastructure. Since 2003 I have been a member of the duty team and have been involved in the response to many volcanic events. I am currently studying for a PhD in geophysics (investigating changes in gravity fields that occur prior to and after eruptions) and will return to GeoNet/GNS Science in 2018.
In July 2001 when GeoNet started, I was working for GNS Science as a Volcanology Technician, working on aspects of physical volcanology (rocks and pumice). I’m currently on leave completing my PhD on geothermal field stratigraphy.
In July 2001 when GeoNet started, I was in 6th form (Year 12) at Tauhara College in Taupo. I started at GNS Science in 2002 as a summer student, and went on to do my PhD at Massey University, which included reviewing New Zealand's Volcanic Alert Level system in 2014. Today I am a Hazard and Risk Management Researcher in the Social Science Department at GNS Science.
In July 2001 when GeoNet started I was working for GNS Science in the volcanology section as the Volcano Monitoring Coordinator (monitoring was part of research then). I have been involved in volcanology for over 40 years (started with DSIR). I have been involved in numerous volcano crises in New Zealand and the south-west Pacific. Today I'm the volcano communication specialist for GeoNet, contribute as a duty officer, the routine volcano monitoring and outreach functions of GeoNet and GNS Science.
In July 2001 when GeoNet started I was working for GNS Science as a Volcano Geophysicist. I was working on models of the seismic activity that may occur before a large volcanic eruption and monitoring earthquakes at geothermal systems and the active volcanoes. Today I’m a Senior Volcano Geophysicist still, with interest in earthquakes at geothermal systems and the active volcanoes and how GeoNet deals with data.
Working our way south we start at Monowai in the northern Kermadecs. Monowai is a submarine volcano about 380 km northeast of Raoul Island (or 1400 km northeast of Auckland) and the summit lies about 100 m below the sea surface. Volcanic earthquake activity from Monowai appears on the seismograph at Rarotonga hence we are able to follow the activity. Routine aerial patrols by the RNZAF confirm the activity. The RNZAF pass on pictures of plumes generated by the activity. Activity is regular and noted 3-10 days a month, making it one of our most active volcanoes at the moment.
Following a sequence of earthquakes that lasted several days (but stopped 3 days before) Raoul Island erupted without warning at around 8:20 in the morning of 17 March 2006. The eruption continued for around 30 minutes and created several new vents within and near Green Lake. Scientists found no evidence for new magma associated with this eruption and believe the eruption was caused by a pulse of volcanic gas and volatiles been released from depth which accumulated beneath a sealed hydrothermal system until the pressure was great enough to blow the seal and cause the eruption. Tragically, a Department of Conservation employee was killed by this eruption. Following this eruption GeoNet worked with DOC to further enhance the monitoring programme on the island.
Large pumice rafts were identified near the Kermadec Islands in early August. Analysis of remote sensing data (satellite images) has shown that these came from a submarine eruption at Havre submarine volcano around 17-18 July 2012. Havre lies about 230 km SW of Raoul Island or 860 km NE of Auckland. The pumice extended in a north-east direction for about 280 km in late July and was reported over 600 km long later in August. Havre Seamount was confirmed as the source following a science cruise by NIWA.
50 km off the Bay of Plenty coast lies White Island (Whakaari) an iconic view as one drives along the coast. In 2011 volcanic unrest started at Whakaari, the Crater Lake started to heat and shrink. Following a rapid water level rise (27-28 July) the volcano started erupting explosively on 5 August 2012, being followed by a period of ash emission. In late November 2012 a small lava extrusion was visible. Geysering activity was common in the reforming lake during early-mid 2013. This was followed on 20 August 2013 by an explosive eruption, with more explosive eruptions on 4, 8 and 11 October. The Crater Lake re-established after this and the water level rose. The level of volcanic unrest was variable in 2014-15. On 27 April 2016 further violent explosive eruptions occurred at White Island.
Around mid-night on 6 August 2012 the upper Te Maari crater on the north side of Mt Tongariro burst back into life after 119 years of quiescence. Te Maari had experienced local earthquake activity for 4 weeks and changes in the volcanic gas output. This short period of unrest enabled some preparatory actions by responding agencies and local residents. The 6 August 2012 eruption ejected blocks over 6 km2 and a debris flow occurred down a valley to the west, with minor ashfall occurring as far away as Hawkes Bay. The debris flow changed drainage and formed ponds, which broke out later forming small lahars. A semi-circular rift had formed south of upper Te Maari Crater, containing many small vents. A further explosive eruption occurred on 21 November. Minor remobilisation floods have continued. The output of volcanic gas declined after the eruptions.
On 4 October 2006 the GeoNet monitoring equipment detected what appeared as a small volcanic eruption at Ruapehu. It wasn’t until the weather improved 2 days later that the eruption was confirmed. A small hydrothermal eruption had occurred with the effects of the eruption been confined to the lake basin and having only minimal impact. There was evidence of wave action up to 4-5m above the lake surface; this was not high enough to flow over the tephra dam that blocked the outlet and generate a lahar at that time.
Mt Ruapehu erupted again on 25 September 2007 and produced two lahars, a moderate eruption column to about 15,000 feet, with ash fall and rock falls across the summit of the volcano. This eruption was similar to the 1969, 1975 and 1988 eruptions. It was smaller than the 1969 and 1975 events, but larger than 1988. All evidence available indicates the eruption was hydrothermal in nature. A ballistic (rock fall) apron extended north from the lake, and actually exceeded the ash fallout zone. Typically ash travels further than the heavier ballistics, however in this case the ballistic rocks were ejected with sufficient force to out-travel the lighter ash material. One lahar travelled approximately 1 km into the Whakapapa ski field, reaching half-way down the Far West T-bar to an altitude of c. 2100 m. The other snow slurry lahar travelled down the Whangaehu River, leaving a deposit c. 80 m wide and 1 - 3 m thick near the Round-The-Mountain track bridge 7 km from Crater Lake.
Not to be left out in 2006 Ngauruhoe reminded us the he is still an active volcano when a period of volcanic unrest started in May. The seismic activity around Ngauruhoe increased above the typical background level in June so the Volcanic Alert Level was raised to Level 1. 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. After mid-2008 the number of earthquakes returned to a typical level of a few per week or less. This increase in earthquake activity did not necessarily mean that an eruption is imminent. The Volcanic Alert Level was lowered to Level 0 in December 2008.
To get around this volcanologists use two display techniques called RSAM and SSAM. RSAM stands for Real-time Seismic-Amplitude Measurement. It represents the overall signal size over periods of 10 minutes. While SSAM stands for Seismic Spectral-Amplitude Measurement. It shows the relative signal size in different frequency bands. Different seismic signals have energy at different frequencies. These tools do help use differentiate the source of some common seismic signals like surf, wind, volcanic tremor and traffic.
A problem with RSAM is that it measures the overall signal size regardless of what produces the signal. If the signal is caused by volcanic tremor then RSAM is very useful. But when the wind blows strongly the RSAM value will still go up and scientists don't learn anything about the volcano, only the weather! The key is to look at RSAM and SSAM plots together. RSAM will give us a measure of the signal size and SSAM more information on the likely source of the signal.
The examples below show the effects of the gales at two of our sites; Ngauruhoe and Karewarewa.