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 »
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 »
See the video of our visit to White Island: Here’s a bit more about what we did during our day on there: Karen and Agnes set off with their water monitoring equipment, whilst Brad, Steve and I started the elevation survey, measuring height differences between an extended series of fixed points that had been marked by wooden stakes driven into the ground. Whilst Steve held the survey pole, Brad aimed his leveler at it from an adjacent measurement station and was able to read off the height difference between the two points. By sighting between the points in this way, we continued our survey past some very loud and active fumaroles, in a broad area towards the crater lake. Occasionally we stopped to take photographs of interesting features, or discuss the history of the formations around us. Once or twice we were enveloped in steam and gas from the fumaroles, and rained on by acidic water droplets (acid rain) that gave a burning, prickling sensation to my eyes. Past measurements have shown that the ground near the crater has been rising by two or three centimeters every three months for several years, mainly due to an increase in heat in the ground. From our measurements we found that the hottest area of ground near the most active fumaroles had risen up to a maximum of 50mm since the last survey, with the amount of uplift reducing quickly a short distance away. These results show continuity with the long term trend of uplift. Almost towards the end of the survey, we met up with Karen and Agnes, and I watched them sampling the water from a very active hydrothermal spring that was gushing and splashing nearby. To make a variety of measurements of the water chemistry and isotopes, they scooped water out of the spring and put it into various sampling bottles. Once our survey was done, Brad and I walked over to the lower of two webcams to give the glass a wipe, as the photos had been getting quite fuzzy due to a build up of dust. There in front of the camera was ‘Dino’ in real life. He is a small dinosaur, apparently famous the world over for having arrived mysteriously to take up residence in full view of White Island’s Crater Webcam some years ago: see http://www.geonet.org.nz/volcano/activity/white-island/cameras/whiteisland-latest.html Before we returned to the helicopter, we walked through the ruins of the old sulphur mine, where there were rusted machines and derelict buildings. Finally we were ready to leave and as we turned in a wide loop above White Island, I was very impressed to have been able to have had such a close encounter with such a remarkable place.
Last week I visited the GNS Science office at Wairakei, just outside Taupo. This is where a lot of research is done into New Zealand volcanoes and geothermal fields. First up this morning was a trip to White Island, One of the most frequently active volcanoes in New Zealand, where I assisted a small team of volcanologists on one of their routine visits. The purpose was to test the chemistry of the groundwater appearing out of numerous springs around the crater area, as well as to survey the ground surface elevation to check for sinking or uplift. In the team were GNS scientists Karen Britten, Agnes Mazot, Brad Scott and Steve Sherburn. White Island is 50km north of the Bay of Plenty coast, visible from nearby towns and often seen to be emitting a plume of steam. From the mid seventies to the year 2000 it was frequently in a state of eruption. Since then it has quietened down to become relatively peaceful for the last few years.For our visit we flew by helicopter from Rotorua, first across beautiful farmland and large pine forests, then out to sea where White Island soon loomed up in the distance. I had seen many photos of the island before but was excited to have the opportunity to actually set foot on it in reality. It is a horseshoe shaped island, with a high surrounding ridge around the inner crater area that includes a large yellow greenish crater lake. This lake formed after the most recent eruption phase and is only about 6 years old. On the South East side the ridge is breached in a couple of places, where the land slopes gently to the sea shore at a low angle. On our arrival we flew in from this side, and landed in the hummocky area a couple of hundred metres in from the shore.Our pilot switched off the engine, and immediately the sound of hissing and gushing fumeroles dominated. There was a strong smell of sulphur and clouds of steam wafting up from numerous points further in towards the centre of the main crater. The ground was littered with blocks of scoria and lava bombs from past eruptions. The photo shows a lava bomb that was molten when in landed on top of another rock, before it solidified.