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The Auckland Volcanic Field (AVF) is uniquely different from the well-known volcanoes in New Zealand in that each eruption occurs from a new location and the volcanoes do not erupt twice; Rangitoto is the only known exception, as it has erupted at least twice. Globally very few eruptions have occurred historically from volcanic fields so we do not have a lot of knowledge of what happens before an eruption. Traditionally, monitoring an active volcano is based around recording seismic signals, ground deformation and gas or water chemistry. When we do not know where the next vent might be we are left with just one method to use; earthquake recording.
The DEVORA research project has been looking at many aspects of volcanic activity in Auckland, including possible eruption precursors. This has involved looking for historical examples of similar eruptions elsewhere in the world. Was there volcanic unrest? How did it manifest? One of the common unrest indicators is earthquake activity. Another clue can be found in the rocks that the volcano has erupted. Many signals are preserved in the crystals and they tell us about the journey the rocks have been on. From this work, we know the Auckland magmas start out from great depth (80-100 km). We also know that they rise relatively fast and don’t appear to stall on the way. What is not clear is what signals these processes will make. Will they make many or just a few earthquakes? How big will the earthquakes be? What type of earthquake will they be? Will there be volcanic tremor?
Based on these challenges GeoNet has had to devise the monitoring in Auckland around a seismic network that covers all the known locations of volcanoes. The Auckland Volcanic Field spans about 27 km north-south and 19 km east-west and underlies a major city. There is no geothermal system and we will not see any ground deformation until shortly before the eruption starts. The greatest issue is cultural noise (the city) and this stops us seeing small earthquakes. This is overcome by using borehole sensors. Auckland Regional Council (ARC) started building a near-real time seismic network in 1993 with NZ Geological Survey and this was operational from the mid 1990’s. The network was connected to the GeoNet project in 2003. At that time, there were 5 seismic sensors in the Auckland area, four of which were in boreholes.
Starting in 2006 GeoNet upgraded the network by adding 3-component sensors and then by adding more borehole sensors and increasing the area covered. Today the seismic sensors in Auckland are fully integrated into GeoNet. We operate seven 3-component borehole sensors, 1 single component borehole site, three 3-component sites and 4 strong motion sites. Since 1994 we have recorded and located 372 earthquakes in the greater Auckland area, about 16 a year. None of these appear to be related to volcanic processes.
Like everyone else the volcano team has been waiting on summer to arrive, so they can catch up on or complete a few outstanding tasks. Last week summer called by for a couple of days and the team visited White Island (Whakaari), completed a gas flight around Ruapehu and visited the Crater Lake at Mt Ruapehu.
As part of the monitoring at Mt Ruapehu we attempt to sample the Crater Lake about once a month. This allows us to collect water and gas samples and confirm the temperatures from the data logger probe in the lake. The lake was successfully sampled last Saturday. The lake appeared a uniform grey colour as it has on past samplings. This indicates there is some convection (mixing) occurring in the lake as the gases and hot fluids enter it. The lake was overflowing, which is normal for the lake and varies little. The temperature of the Crater Lake is currently around 21 °C and is slowly cooling. A gas flight was also completed on the 24th. The results from this flight indicate low-moderate amounts of volcanic gas continue to come through the lake. The Volcanic Alert Level for Ruapehu remains at Level 1 (minor volcanic unrest).
White Island (Whakaari)
Meanwhile a visit was also made to White Island on the 27th. We visit the island to make many measurements, this trip was to collect gas and water samples, observe the activity from the active crater and make a soil gas survey. The gas chemists collect gas from the hottest accessibly fumaroles (steam vents). Fumarole #1 is currently the hottest and the team measured 191 °C while sampling it. Basically the same temperature as the previous trip. The activity from the vent in the active crater was also unchanged. The crater floor remains ‘dry’, only a few small ponds and springs are present. The crater lake has not reformed since the eruptions in April and September last year. The soil gas survey measures the CO2 gas leaking from the Main Carter floor. We make measurements at 61 sites. There has been an increase from the measurements in November 2016, some of this is related to the dryer conditions on the island. The Volcanic Alert Level for White Island remains at Level 1 (minor volcanic unrest).
On January 31 University of Auckland geographers noted a volcanic plume on satellite images in the Tonga area. The images show a submarine volcanic eruption is now under way about 46 km north west of Nuku’alofa. Back tracking through images we can trace activity back to 23 January from this volcano. This volcano has been called ‘Submarine Volcano III’ in historic reports.
Submarine volcanic activity has been noted from this area in 1911; 1923 (steam plumes); 1970 (discoloured water); 1989-1999 (small island formed in January 1999) and 2007 (discoloured water and felt earthquakes). The 1999 activity is the best reported, starting with felt earthquakes in late December 1989 and discoloured water was noted on 7 January 1999 and an eruption column on the 8th. A volcanic cone was reported above sea level on January 12 and again in the 14th.
Satellite images obtained from the NASA Earth Science program allow us to back track the submarine activity. We can see activity in images from 23, 26, 28 and 29 January indicating the eruption has been ongoing for over a week. After contacting our colleagues in Tonga it appears a steam plume may also be present, but the local cloud makes this difficult to ascertain. Submarine eruptions can be a hazard to shipping.
Submarine volcanic activity is common in the Tonga area and some produce small islands that last for a few days to months. Examples of this include Curacoa Reef (1973), Home Reef (1984), Metis Shoal (1967-68, 1979, 1995) Falcon Island (1927-36) and Hunga Ha’apai 1988 and 2014-15).
A short-lived, steam driven eruption occurred from Upper Te Maari crater on 6 August 2012. This was the first eruption from Te Maari (Tongariro) since 3 February 1928. However the largest historic eruptions from Te Maari occurred in late 1896 and early 1897.
120 years ago today (25 January), locals reported the initiation of an eruption from Upper Te Maari, which was preceded by felt earthquake activity. Ash fell on a coach travelling between Ohingaiti and the Whanganui River on 26 January 1897, causing restricted visibility. This eruption was the first since 21 December 1896.
In the night prior to the first eruptive outburst in 1896, more than 140 earthquakes were felt by the local population at Tokaanu. A series of eruptions started at Upper Te Maari crater on 13 November 1896, extending through to October 1897. After 11 days of “not…much sign of activity”, Upper Te Maari crater erupted again on 24 November 1896. In addition to Ngauruhoe, Red Crater reportedly “held fire dances”. Ash-producing eruptions occurred most days between 24 and 30 November 1896, with stronger eruptions on 27 and 30 November.
Eruptions continued on the morning of 1 December 1896, and throughout early December. On 11 December 1896, roaring and thundering noises were heard for “some” minutes apparently coming from the crater, but aside from a blue-coloured gas in contrast to the white steam emitted from Ketetahi, no sign of an eruption was seen. An eruption column was observed on 15 December 1896, lasting for 15 minutes, and was reported to have a dark-red glow at the base, lightning in the column, and incandescent blocks/bombs ejected on parabolic paths. Local reported the countryside was coated in ash to a depth of several inches, weighing down vegetation. Extensive ash fall, was also observed in Napier. Upper Te Maari crater was reportedly still active on 21 December 1896, “ejecting steam, ashes, and smoke”.
Monitoring volcanoes has many challenges; a couple being how do we see at night and how hot is that vent we can see? Is it heating or cooling? One of the technologies that has helped us a lot is web cameras and another is handheld Thermal Infra Red (TIR) cameras. What if we had both in one unit! Web cameras work well in day light and when the lens is not covered in dust or sublimates from the volcanic plume. Recently the security industry has developed thermal sensor modules (TSM) to improve night views and these are now able to also run as ‘web cameras’. It doesn’t take long before our technicians could see the potential for volcano monitoring.
So where better to test this idea than at White Island, after all it is an active volcano. In fact our most active at present, last erupting in April and September 2016. Since we need to understand how volcanoes work and what they are up to is a big part of our monitoring it sounds perfect. A camera that works 24 hours would be a great tool. Even better if it can tell us something about the temperatures as well.
A TIR camera measures the emitted energy from the surface it is looking at, with more energy coming from hot surfaces than cold ones. The camera collects the data digitally and then applies a ‘false colour’ to make an image. One of the advantages is images can be collected at night (plus day), while our traditional web cameras see little at night unless the moon is out. The thermal sensor module will potentially give higher quality data with spatial coverage of areas around the vents as well and appears to be cost effective.
We recently took the thermal sensor module (TSM) to White Island to learn about the data quality, thermal range, spatial cover and the effect of steam and gas on the path between the sensor and feature we are looking at. We also plan to make use of it at other volcanoes and geothermal systems to learn about its capabilities. One constraint on all web cameras at active volcanoes is the lens has to be protected. For the TSM to work this has to be special material to allow the emitted energy (electromagnetic waves) to pass through. We are not sure how the acid rain will affect this. Just one of our many challenges. If we can make all this work it will improve our understanding of how volcano systems work and better inform us about the hazards and risks from volcanoes.
In recent years Unmanned Aerial Vehicles (UAV’s) or, drones, as they are often called, have become a useful tool in going places that are often difficult or dangerous for people to go. We have been using them to make observations of locations that are not safe to visit and making maps of areas. In June we mapped the eruption deposits at Waimangu by UAV and more recently used them extensively to map the fault displacements and landslides produced by the M7.8 Kaikoura Earthquake. In late December we were able to fly the active crater at White Island.
While we have the volcano cams on the island, these are stationary and don’t give us the kind of rich data that a drone can. Since the eruption in late April 2016 the vent area has often been obscured by steam and gas and a small lake also formed for a while. This made it difficult to fully assess the changes to the active crater area. We were able to work out the crater floor was lowered by about 13 m but couldn’t accurately estimate the volume of material erupted as we didn’t have a before and after map. Understanding the volumes involved, distances material was moved etc. helps us better interpret the impacts and mechanism of the April eruption.
We were able to obtain images of the active crater area usually obscured by the gas and steam plume so we could make a new map and Digital Terrain Model (DTM) of the area. We know some of the crater floor was lowered about 13 m by the April eruption, but didn’t have any data on the vent area. During our visit in December we had a light easterly wind blowing the plume away from us and the humidity was low so the amount of steam was also low. Perfect conditions for flying the UAV mission over and in the crater.
Our UAV technician has processed the images and video captured on the day and is now compiling the DTM and surface maps. They are really impressive and are giving us a new insight to the changes within the active crater.
No word yet on what Dino thinks of this new visitor to the island.
White Island (Whakaari)
On November 21 we completed a gas flight at White Island, where we measure sulphur dioxide (SO2), carbon dioxide (CO2) and hydrogen sulphide (H2S). The gas output was down slightly on the October flight. The sulphur dioxide (SO2) has ranged 230-420 tons per day, carbon dioxide (CO2) 1240-1730 tons per day and hydrogen sulphide (H2S) 15-35 tons per day.
The main vent(s) were less audible than in October, still producing a transparent plume at the base/vent which evolved into a vivid white steam plume. There is no lake. Over the last 2-3 months the small lake let on the crater floor was disappeared to leave 5-6 small depressions, some have water ponded in them. The water levels are variable as are the colours of the pools, some are grey and active, others blue/green and passive. We estimated the water levels varied by 2-3 m.
A levelling survey was completed on December 20 to ascertain the amount of ground deformation across the crater floor. Changes show subsidence (20 mm+) focused on the active crater area. Fumarole ‘Zero’ remains very hot, we measured 182 °C. It was 178 °C in October.
We used drones to obtain photography of the active crater area so we can build a new map. We also sampled the gases from the main gas plume using a drone. Maintenance was also completed on the web cameras.
On December 17 we completed a gas flight at Ruapehu, our first successful flight for months. We measure sulphur dioxide (SO2), carbon dioxide (CO2) and hydrogen sulphide (H2S). The gas output was up slightly on the August flight. The sulphur dioxide (SO2) has ranged 19-22 tons per day, carbon dioxide (CO2) 240-640 tons per day and hydrogen sulphide (H2S) 0.6-1.6 tons per day since July.
The Crater Lake was visited to sample the water and collect gases on December 20. The lake temperature was 21.7 °C. Lake was a battleship grey colour with more blue grey water near the lakeshore due to meltwater going into the lake. The central vent was very slightly distinguishable in the right light conditions. The north vent area had a lot of sulphur slicks nearby.
Lake level appeared to be on the high side (summer melt) and the flow at the outlet was estimated at 60-80 L/sec.
Crater Lake temperature has been cooling since early October, when it reached 40 °C. For the last 2-3 weeks it has been around 24-22 °C.
As part of a collaboration with the University of Toronto (Canada) several passive air samplers are being installed on the active volcanoes and in large geothermal areas. These will measure mercury and its isotopes concentrations. The main purposes of the project are to characterize the sources of Mercury and monitor the spatial distribution of Mercury into the atmosphere.
Volcano rundown: let’s start at the top
Starting offshore North of New Zealand, we work our way south along the Kermadecs, beginning with Monowai submarine volcano. There has been no activity noted since 11-12th November. However, we did notice a random pumice raft in the middle of the ocean near Tonga but this looks unrelated to Monowai.
Next is Raoul Island, nothing new is apparent there, only the Crater Lakes showing their usual summer warming cycle, due to the warmer weather.
A team visited White Island (Whakaari) and our ever watching Dino, last Thursday with a film crew and made several observations. The temperature of the main vent in the active crater has declined, down from 280 to around 140 °C. The small pools of water on the crater floor are getting smaller. The temperature of the hottest accessible fumarole (steam vent) remains around 180 °C. The gas flux has varied from around 300 to 600 tons per day of SO2. Overall the situation remains very similar at White Island (Whakaari) to how it was a couple of weeks ago.
Auckland Volcanic Field is also quiet too, no earthquakes near there. Moving south, Okataina Volcanic Centre (this includes Tarawera) is quiet, just a couple of small shallow earthquakes nearby.
The big news in volcano land this week is the that there has been a small steam (hydrothermal eruption) in Lake Rotorua. Eruptions have been known in this area all through our written history (1830 – present), so it’s not too unusual. The occurrence of steam eruptions has been variable in Rotorua, with many during the exploitation of the geothermal system, however they declined after the bore closure (1987). The last significant one was in 2001. We’ll be keeping a close eye on this latest hydrothermal eruption but, as this is pretty much business as usual for this system, we aren’t too concerned about it. We went down to check out the eruption and it didn't leave much interesting evidence
Our central volcanic zone is pretty quiet too. Taupo Volcanic Centre is quiet, just a couple of small earthquakes. Further south, the Tongariro-Ngauruhoe area is very quiet, again just a couple of small earthquakes. A team visited Te Maari and measure 308 °C from the vent here. The volcanic tremor at Ruapehu remains weak. The lake temperature is now 24.5 ˚C, continuing to slowly decline.
Mt. Taranaki continues its silent watch over the West Coast of the North Island.
So that ends our tour. And thankfully, it looks like the volcanoes have continued to ignore the Kaikoura earthquake sequence.
A RNZAF flight on Wednesday November 16 has reported floating pumice to the west of Minerva Reef in an area about 600 km SE of Fiji and 500 km SW of Tonga. We are not aware of any active submarine volcanoes in this area. The nearest active submarine volcano is Monowai (400 km SE) and we know it was active on November 10-11. Monowai usually does not produce pumice rafts, just discoloured plumes.
We have analysed some satellite images from the area using https://worldview.earthdata.nasa.gov/ and can see the pumice rafts in images from November 15 and 16. They extend for more than 100 km in the images. We have not as yet been able to ‘back track’ the pumice in older images to confirm a source location. The pumice is generally seen around 179°W and 179°E and 23° 20” S.
In October 2012 a much larger pumice raft was found (https://goo.gl/8A7c57) and later we found out it came from Harve submarine volcano.
Volcano rundown: let’s start at the top
Starting offshore North of New Zealand, we work our way south along the Kermadecs, beginning with Monowai submarine volcano, which had a brief bit of activity over the 11-12th November that lasted about 24 hours. This is normal behaviour as we see a few days’ of activity every month. Next is Raoul Island, nothing new is apparent there, only the Crater Lakes showing their usual summer warming cycle (climate induced). And it’s a similar situation at White Island. The volcanic tremor levels remain very low and although there have been a couple of earthquakes nearby we see that every other week as well. Auckland is quite too.
Moving on-shore, Okataina Volcanic Centre (this includes Tarawera) is quiet, just a couple of small shallow earthquakes near Kawerau and a half dozen to the south in Waikite Valley (a place no stranger to small earthquake swarms). There were also a couple of earthquakes near the Wairakei geothermal system. Taupo Volcanic Centre is quiet, just 2 events so far this week.However, it is a very different story north of Kuratau (near Turangi) which experienced a sequence of earthquakes between the 10th and 13th of November. We had the story ready to run on Monday, but decided to hold off publishing it because we were focused on the bigger issues of the Kaikoura earthquake.
The sequence has come in four parts to date:
- The first, which included the largest earthquakes, started on November 10 and appeared as a typical main-shock after-shock sequence. The largest of the 27 earthquakes in this part was a magnitude 3.3.
- After a quiescence (aka a geological power nap) of about 21 hours, the second sequence started. It behaved much more like a typical Taupo Volcanic Zone swarm and included 52 earthquakes.
- The third part of the sequence started about 11 hours after the second and was also swarm like (32 earthquakes).
- The fourth part included three magnitude 3 earthquakes and an isolated magnitude 3.2 earthquake on the eastern side of the lake (9 events). This part dropped off before midnight Sunday/Monday and so far has not notably reactivated following the M7.5 sequence - i.e. since the first Kaikoura earthquake.
The earthquakes range in magnitude from a little less than 1.0 to magnitude 3.3. The earthquakes are located between 5 and 11 km deep, with the majority of these between 7-8 km. Small shallow earthquakes like these will be well felt by local residents and we have received many felt reports from the area. It is not clear if the sequence has finished yet. Prolonged earthquake swarms (sequences) are a regular feature of the Taupo Volcanic Zone. One near Matata in the mid-2000’s lasted several years.
Further south, the Tongariro-Ngauruhoe area is very quiet, just a couple of small earthquakes. The volcanic tremor at Ruapehu is slowly declining, heading back towards normal background levels. The lake temperature is now 31 ˚C, slowly declining from the recent maximum of 39 ˚C.
Mt. Taranaki continues its silent watch over the West Coast of the North Island.
So that ends our tour. And thankfully, it looks like the volcanoes have ignored the Kaikoura earthquake(s).
An increase in the strength of volcanic tremor began on October 18, where a sharp increase was noted before the energy declined a day later. Subsequent tremor increases occurred again on October 25 and 28, and currently remains higher than normal. These tremor pulses do not appear to be related to any variation in the lake temperature. Our records show that similar periods of increased volcanic tremor were present May-June 2016, again when the lake temperature was high. Importantly, no eruptive activity or geysering was noted in Crater Lake during the previous periods of volcanic tremor.
Weather conditions have not been ideal for mountain observations. Nevertheless, our scientists will be visiting the lake to collect water samples for further analysis and making a gas flight when the weather conditions improve.
The active crater at Mt Ruapehu is occupied by Crater Lake and it displays temperatures that typically range between about 15 and 40°C and the phases can last between about 9 and 20 months. The lake cooled to a minimum of 12°C in mid-August and then remained at 13-14°C until early September when it started to heat again and reached a peak of 39.8°C on October 4.
GNS Science volcanologists continue to closely monitor Ruapehu through the GeoNet project. The Volcanic Alert Level for Mt Ruapehu remains at Level 1 (minor volcanic unrest) and the Aviation Colour Code also remains unchanged at Green. 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.
Following the 1995-1996 eruptions of Mt Ruapehu, which were the largest eruptions in New Zealand for 50 years it was realised there was a need for more detailed education about ‘The Volcano Problem’. In December 1997 GNS held its first volcano short course; Volcanoes and Society in Taupo. Now 19 years later the course is still popular and fulfilling a need with emergency managers and operational staff, engineering lifelines, the Ministry of Civil Defence and Emergency Management, students, communications specialists and staff from a SW Pacific volcano observatory.
In 1997 the course covered off: The Volcano Problem, Volcanic Impacts and Mitigation, Volcano Surveillance, Warnings and Alerts and Planning to Respond. In 2016 the course covered: The Volcano Problem, Near Vent Hazards, Volcanic Ash Impacts, Ash and Gas Impacts on Health, NZ Volcanoes, The IWI perspective, GeoNet Volcano monitoring, Warning Communications, Challenges of Modern Media, Communicating Hazard and Risk, Management of Risk and case studies. The content has grown as have the issues we face from volcanoes. This year 15 people attended the course and the Field Trip.
Presenters came from a variety of organisations, including the University of Hawaii, GNS Science, Joint Centre for Disaster Research, BOP Emergency Management, the Ministry of Civil Defence and Emergency Management and Auckland University. Two of the presenters also presented on the 1st course back in 1997. The field trip covered an introduction to ‘Caldera Volcanoes’, aspects of geothermal hazards, volcanic land forms, the 1886 Tarawera eruption and faulting associated with the large caldera volcanoes. The course was well received by the participants. The 2017 course will mark the 20th running of the Volcano Short Course.
Recently we had a short lived episode of volcanic ash emission at White Island and our geologists collected some samples. The ash was what geologists call ‘very fine’, that is the particles are very small. They reported back to us that the ash ‘didn’t show any signs of new magma been involved. So how do they know this?
The traditional method is to place the ash sample under a microscope and describe what you see. This time around they did that, as well as putting some in the new Scanning Electron Microscope (SEM) that our geothermal team has obtained. It has very powerful electron optics. One of the features of an SEM is that you can get up to 60,000X magnification. With this extra magnification we can see all sorts of detail in the ash fragments.
Below are two images of volcanic ash. In the right image is some ash from Yasur volcano in Vanuatu. Here explosions happen very 5-10 minutes from craters full of molten lava and the explosions produce a volcanic ash that is made up almost entirely of fresh magmatic particles. You can see the indentations from the gas bubbles and the ‘long’ needle like structures of the volcanic glass.
In the other image is some of the ash we collected from White Island last week. You can see it is made up of lots of angular fragments and crystals. Most of this sample is broken up rock and crystal. This sample is a marked contrast to the one from Yasur. As we can not see any fresh magmatic glass or material with gas bubbles, we are confident there is no new magma at White Island. The new SEM is going to be a big help when it comes to looking at fine ash samples from our eruptions.
Volcanic ash hazards can be very far reaching and are disruptive and damaging. Volcanic ash affects more people, infrastructure and life than any other eruptive phenomena. It consists of very small jagged pieces of rock and volcanic glass. Ash is abrasive, mildly corrosive and conducts electricity when wet. It does not dissolve in water.
VOLCANIC ALERT BULLETIN: WI – 2016/13
15:20 Monday 3 October 2016
Volcanic Alert Level 1 (no change)
Aviation Colour Code: Yellow (no change)
Recently we have also experienced some issues with the power supplies for some of our remote monitoring gear, mostly related to the accumulative effect of the weather (little sun) and ash on the solar panels. One of the cameras had an issue with the data card. On Friday a team visited the island armed with a new camera, batteries, glass cleaning gear, thermal IR, and gas measuring equipment.
The easterly conditions prevailing when the team got there restricted their access to the summit area. This meant the West Rim camera couldn’t be replaced and they were also unable to make detailed gas measurements as planned. They could visit the other two cameras, clean them, and swap out the batteries. They also visited the larger fumarole, known as F0 and measured its temperature. This had increased about 9 °C and is now 190 °C.
Ash emission has ceased, however White Island is always capable of a new eruption at any time, without any useful warning. We continue to monitor the volcano for possible renewed activity. The Volcanic Alert Level remains at Level 1. The Aviation Colour code remains Yellow.
This morning, steam plumes have been visible above Mt Ruapehu’s Crater Lake. The lake temperature is now 37 ºC as part of a heating episode that began around 2-3 September 2016. No seismic or acoustic activity has been recorded this morning, indicating the steam plume was not generated by activity in the lake. The Volcanic Alert Level for Mt Ruapehu remains at Level 1 (minor volcanic unrest) and the Aviation Colour Code also remains unchanged at Green.
The active crater at Mt Ruapehu is occupied by Crater Lake. Crater Lake displays temperatures that typically range between about 15 and 40 °C and the phases can last between about 9 and 20 months. The lake cooled to a minimum of 12 °C in mid-August and then remained at 13-14 °C until early September when it started to heat again. Based on past experience, as the lake continues to heat up, more occasional steam plumes can be expected. This is often controlled by atmospheric conditions near the mountain.
There have been no local volcanic earthquakes or changes in the levels of volcanic tremor this morning on the GeoNet instruments at Ruapehu. GNS Science volcanologists continue to closely monitor Ruapehu through the GeoNet project.
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