If you had to work out the daily quantities of different gases coming out of a volcano and spreading across the sky in a huge, mostly invisible plume, where would you begin? This video gives a brief introduction to how New Zealand’s GeoNet scientists go about it: The information is combined with other evidence such as seismic monitoring to judge the risk of future volcanic eruptions.
Volcano Gas Flights Video Read More »
My next experience of a GeoNet gas monitoring flight was over Tongariro and Ruapehu. This time Karen Britten and I were joined by Fiona Atkinson (left in photo) who is part of the GeoNet volcano monitoring team. As we approached the volcanoes from over Lake Taupo, the small gas plume from Te Maari was visible. Because the plume is quite low against the mountain side, GeoNet cannot always monitor it by plane. They sometimes use a road vehicle instead, traversing under the plume along a nearby road.Our flight took us past the Red Crater (left) and the Emerald Lakes, where I had been tramping a few days before. North Crater on the right skyline is a solidified lava lake, whilst the dark lava flow in the middle distance on the right originated out of Red Crater. We circled Ngauruhoe several times just in case there was some evidence of gas emission, although non could be determined. If you click on the photo to enlarge it you can just see some people on the left hand side of the inner crater rim. The crater lake of Ruapehu was a uniform pale blue colour, with no visible upwellings. Our gas measurements showed about 670 tonnes per day of CO2 , a little H2S (0.5 t/day) and about 28 tonnes per day of SO2. These figures are in a similar range to those from the end of January, but somewhat elevated compared to December. On the way back we decided to take a closer look at the Upper Te Maari crater area. There is still a lot of grey ash covering the area from the November 21st eruption, and yellow sulphur deposits around the fumeroles. Having landed back in Taupo, I drove down to Whakapapa Village, and was able to look at the Te Maari area from the road on the way. The area affected by ash can be seen extending across the mountain side.I decided that I just had time at the end of the day to walk up Te Heuheu peak on Ruapehu. It is on the north edge of the summit plateau. The crater lake is just beyond the sunlit snow in the centre of the photo, out of sight behind the ridgeIn case you haven’t seen in yet, here is a video of the Te Maari eruption made from the webcam shots on November 21st:
Flight over Tongariro and Ruapehu Read More »
Yesterday I joined Karen Britten on a GeoNet gas monitoring flight over White Island. This was to check the flux of volcanic gas emissions following an ash eruption a few days ago.Check this GeoTrip page if you are interested to visit White Island / Whakaari yourself: www.geotrips.org.nz/trip.html?id=541 ) The plane is modified to allow the equipment to extend outside so that the measurements can be made. carbon dioxide (CO2), hydrogen sulphide (H2S) and sulphur dioxide (SO2) are the most common volcanic gases and are all measured during a gas flight. Approaching White Island, we could see the plume extending first vertically, then off to the West at an altitude of about 2 000 feet. In the distance you can see a grey haze in the sky which is the extension of the plume. Our first task was to fly in circles at constant (neutral) throttle. Through using our GPS to measure our ground speed, we could calculate the effect of the wind on the plane, and thus work out the wind direction and velocity. The track of the plane is visible on the computer screen. Next we flew under the plume at right angles to the wind direction and at the lowest permissible altitude of 200 feet. A Correlation Spectrometer (COSPEC) looks upwards through the plume and measures the amount of ultra violet light being absorbed by the sulphur dioxide. We passed under the plume several times in order to get an average reading. The wind speed is also taken into account to calculate the SO2 flux with this method. Next we flew in wide arcs through the plume, at a radius of about 3 kilometres from the crater. We worked our way contouring back and forth, rising 200 feet each time to get a total profile of the gases through the whole plume. Later in the day Karen was able to process the data to show that the daily flux of SO2 was about 600 tonnes. This is at a relatively elevated level compared to mid January, but has not changed much in the last month. Here are the complete data that Karen processed after the flight, comparing them also to the two previous gas flights: Lastly we flew close to the main crater to get a look at the changes that had occurred in recent days. Most of the gas emission was coming from a small crater or tuff cone, and there seemed to be an area of red brown which is probably ash from the recent eruption. Back in Taupo after a total flight time of about 4 hours, I had this evening view across the lake to Tongariro. The Te Maari crater was producing a thin plume of its own extending across the sunset.
White Island Gas Flight Read More »
GNS Science volcanologists recently set up an experiment to test the seismic velocity of the rocks that make up White Island. Over the last few decades it has been New Zealand’s most active volcano and has produced minor eruptions in recent weeks. (For its present activity status click here.) Velocities of seismic waves through the Earth can vary considerably because of variations in the density and layout of different rock types. It is important for scientists to know these subsurface seismic velocities as they are used to calculate the locations of earthquakes under the volcano. These might indicate rising magma and therefore an impending eruption. It is for this reason that volcanic earthquakes are carefully monitored. For an explanation of how earthquakes can be located see this video, and for a look at White Island’s activity status, including the seismic drum, click here. There are various ways to generate seismic waves in order to measure velocities, such as by using explosives or air guns. These traditional methods can have environmental, safety or cost drawbacks. So in this case, a GNS Science team, led by volcano seismologist Art Jolly, used a novel method: First of all, The team set up 17 temporary seismometers around White Island, with six of those set up in a line across the volcano crater floor to record the shock waves, their travel times (hence velocity) and their intensities. Three large sacks were then filled up with about 700 kgs each of beach sand… …whilst some of the team laid out large white crosses, held down by rocks or gravel to indicate the target zones for two of the drops. (The third target was the centre of the crater lake). A helicopter was then used to drop the bags of sand from about 400m onto the three target areas. The impacts when they hit the ground (or water) created the seismic waves required. They were also heard from a safe distance as a very loud thwack! The last image shows the seismic wave traces produced by the three impacts as recorded by the nearest seismometer to each impact. The drops were successfully recorded on the temporary stations giving scientists a new velocity model for White Island earthquake locations. Future tests might include heavier weights, greater drop heights and different seismometer locations to add more depth and breadth to the velocity model. (All images GNS Science)
Artificial Earthquakes on an Active Volcano Read More »
Here is our video describing this years Rotomahana explorations – a hidden world come into view!
Seeing beneath the water and mud of Lake Rotomahana Read More »
Following last weeks’ multibeam sonar survey, the bed of Lake Rotomahana has now been mapped to a resolution of half a metre, bringing to light a mass of detail hitherto unknown to scientists. The first photo shows last year’s map which was made with the assistance of WHOI (Wood’s Hole Oceanographic Institution). The resolution of the map is 15 metres. This year, with the help of ixSurvey, we have improved that by 30x (second image). In this post I will show you some of the features that have come to light. The colour scale indicates depths in metres. Red represents the shallowest depths found around the shoreline, down to blue which is deepest in the main central part of the lake. The maximum depth is about 115 metres. The grey area is the land around the lake that is above water level, or very shallow parts of the south side of the lake that were not scanned. Click on the image for a larger view. The map we now have allows close up study of many fascinating features that we can see for the first time. In the third image showing the northern margin of the lake, you can see two explosion craters right on the very edge. They are about 25 metres deep. In the bottom right part of the image is a newly revealed crater, formed at a late stage in the 1886 eruption. Its rim is about 60 metres below the surface, and its floor is at about 80 metres. All of these craters are approximately 100 metres across. If you click on this image of the flat, deepest part of the lake (blue area), you might just discern a faint circular feature just below and to the right of centre. This is also about 100 metres across and may be the outline of a crater rim that has been almost totally obscured by mud, or it may be the lobe shape of a debris flow that cascaded down from the north, leaving a smooth gouge in the slope (upper part of the picture). In the lower (southern) part of the map there are many erosion features visible on the sloping lake floor. On the left of this image you can see some eroded gullies extending down from the red area (-20m) into the blue (-100m). We believe these runnels formed in the few years after the Tarawera eruption, before the lake filled up, rather than that they were eroded after the water level rose. On the right hand side of the image, there is another area of radiating features. These have quite a different character, being less smooth, and with intriguing lines of hollows. These may have formed as a result of the wave like flow of debris down the slope, but we are uncertain as to why they are so different to the features just to the left (west). The southern half of the blue area on the map has a lot of gas activity. This was noticed last year on some of the sidescan images showing plumes of bubbles arising from a pick marked area on the bed of the lake. This activity has increased dramatically in this part of the lake floor since the Tarawera eruption. Now we can see this area of hydrothermal and gaseous activity in detail, with the ‘pock marks’ showing up as a mass of small vents scattered over a wide area. These are each up to a few metres across. A very significant feature that was revealed in last years’ bathymetric map was the ‘spit’ or promontary that is shown on early photographs of the Pink Terraces. It is extending into the lake in the middle distance of this photograph, not far to the east of the Pink Terraces visible in the left foreground. The spit rises several metres above water level. (Image courtesy of the Alexander Turnbull Library, Wellington) On our new bathymetric map we can clearly see the promontary, now with its crest below 50 or 60 metres of water.
Rotomahana’s lake floor prompts many questions Read More »
The Seismic Survey of Lake Rotomahana is proceeding well this week. Whilst it is being led by GNS Science, the University of Waikato and NIWA are providing technical assistance with some of the equipment being used. The first photo shows the survey boat being loaded with the the cable that contains the hydrophones. These pick up the reflected sound waves that are sent down below the surface by the ‘boomer’, the white object in the background, at the end of the pier. In the graphic you can see how the set up works. The boat tows the seismic source (either the low frequency ‘boomer’ or the higher frequency ‘CHIRP’). This sends sound waves down through the water and into the rocks below. These signals get reflected back up from the different rock layers and are received by the hydrophones in the cable floating behind the boat. Lower frequency sound waves can penetrate deeper into the rocks, whilst higher frequencies give shallower penetration, but provide more detail. During our survey we are using the boomer to give an overall view of the lake floor first. We are then using CHIRP to go over specific locations that we want to observe in more detail, such as the sites of any terraces and particular volcanic structures. On this map of the lake floor, you can see how the seismic lines criss cross the lake back and forth to give overall coverage. This is the planning map, but sometimes the scientists change their plans during the survey, depending on the time they have available, and how well things are progressing. Chris Leblanc is set up with all the computer hardware and software to process all the data produced by the survey. He creates graphic cross sections of the lake floor that reveal the sub surface geological features. You can see one of these sections on his computer screen. There has been a great deal of media interest in our investigation of Lake Rotomahana. In the last photo Cornel de Ronde is being interviewed by John Hudson with cameraman Clint Bruce for TV1’s Sunday programme.
Lake Rotomahana Seismic Read More »
By the end of this week, scientists hope to have a clearer picture of how the famous Pink and White Terraces look. Listen to the National Radio interview: (3′37″) Download: Ogg Vorbis MP3 | Embed New Zealand Herald article on the project here
Scientists hope for picture of Pink and White Terraces soon Read More »
This week I am revisiting Lake Rotomahana with Cornel de Ronde and two surveyors from IXSurvey, Mark Matthews and Dave Mundy. Our first goal in this year’s research at the lake is to make the most detailed map possible of the lake floor. Next week we will use this detailed map to help us take a closer look at the areas of the Pink and White Terraces using seismic survey techniques. The mapping survey will also give us a great deal more information about the hydrothermal activity underlying large parts of the lake. Last year, our improved map of the time helped us to identify the comma shaped submerged landform that led us to the remnants of the Pink Terraces. This year we are using a multibeam sonar scanner that is improving our map resolution by at least ten times. We have been witnessing the gradual revelation of fascinating details of the lake floor that shed additional light on the violence of the 1886 Tarawera Eruption and its aftermath. The scanner is housed below the centre of the small motorboat. As we travel over the surface of the lake, sound waves are beamed out in a line downwards and out to each side. The time taken for the soundwaves to return to the on-board sensors from each direction is translated by the computer into a bathymetric map of the lake floor. The initial, ‘uncleaned’ map shows up in realtime on the onboard computer screen, with colours representing different depths from red (shallow) through to yellow, green and blue as the depth increases. In this image, you can see that the boat is mapping a submerged crater at the edge of the lake. As we criss cross the lake, the map appears as if it is being gradually ‘painted’ on the screen. Where the lake is shallow, the width of the scan is narrow, perhaps ten or twenty metres, whereas in the deeper areas it can extend to about 100 metres on each side. It is amazing to be able to watch the lake floor appear in crisp detail before ones eyes, showing many features that were created by the 1886 eruption and then hidden below the water for over a hundred years. There are numerous explosion craters, mudslides, ridges, depressions and pock marked gas vents. Vast streams of bubbles are also picked up by the scanner, showing that the lake floor is still actively fizzing. Many of the deeper gas bubbles dissolve in the water column as they rise up, but in some places they vigorously break out at the surface as you can see in the photo. Here Mark is putting a sound velocity probe into the water to calibrate the sonar survey. The sound velocity depends on the water density, which varies with temperature and dissolved minerals. This is important because the velocity of the sound waves affects the calculation of distances and depths. Just beside the access road to Lake Rotomahana there is a unique geological horizon. The dark line in this freshly excavated roadside outcrop represents the ground surface up to the day before the Tarawera Eruption, ie June 9th 1886. Above the dark line is the mass of erupted pumice known as the Rotomahana Mud that covered the landscape from the early morning on June 10th. A single, dramatic day in time represented in the geological record around Lake Rotomahana! Our investigations next week will attempt to answer the question as to whether the ‘Eighth Wonder of the Natural World’, the Pink and White Terraces still lie largely intact under the mud just like the dark soil horizon, or whether the exposed portions we located last year are all that is left.
Rotomahana multibeam survey Read More »
“If you want to have an insight into a society, just look at the water in the streams and rivers” Uwe Morgenstern, GNS Science’s specialist in groundwater and ice dating, runs a laboratory that is the most accurate water dating facility in the world. His methods are so precise, that they are four times more accurate than the next best lab, out of a total of about 70 such laboratories worldwide. In a nutshell, groundwater dating works like this: Cosmic rays from outer space interact with our atmosphere and form very small amounts of tritium, a radioactive hydrogen isotope with a half life of 12.3 years. This cosmogenic tritium eventually becomes part of the atmospheric water, with one normal hydrogen atom replaced by a tritium atom. As this water (or snow) precipitates and becomes incorporated into groundwater, it is no longer interacting with the atmospheric tritium, and its tritium concentration starts to deplete due to radioactive decay. Measurement of tritium concentrations in groundwater allows the time since it fell from the sky to be calculated, back to a maximum age of about 100 years. Over the last few days I have been out in the field with Uwe and Mike Toews (a groundwater modeller at GNS Science) sampling the streams and springs around Lake Rotorua. The water quality in Lake Rotorua, and the many other smaller lakes in the area, is very important to the local community, for drinking, agriculture, recreation and tourism, including world famous trout fishing. Farming, especially dairy, beef and sheep farming, is also a very important activity around the region. Farm effluent and fertilisers cause nutrients, particularly nitrates, to enter the groundwater and eventually get transported into the lake. As a result the chemical balance changes, with potential negative impacts such as the growth of toxic algal blooms and other ecological changes such as impacts on fish. To understand the effects of land use on the water quality in the ground, in streams, rivers, and lakes, you need to not only monitor the concentration of pollutants in the water, but also measure the age of the groundwater. For this reason, Uwe has been studying the groundwater around Lake Rotorua for a number of years. With such large groundwater systems, it can take many years or decades for polluted water (for example nitrate from farms) to reappear back on the surface in streams and lakes. Because of this time lag, large groundwater systems can silently become contaminated until the contaminated water reaches the spring discharge. Then it will also take the same long time to flush the contaminated water out of the groundwater system. The data Uwe is coming up with shows a range of time spans for the input of lake water, from very quick (months) to over a hundred years in the case of Hamurana Spring. The map shows coloured dots representing the springs and streams that were on our list for resampling. For a news article about the findings of this research have a look here. Here is a video, describing the research and the findings so far:
Groundwater dating around Lake Rotorua Read More »