Volcano Gas Flights

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I’m the very lucky person who works for GNS Science in the volcano monitoring team. Part of the monitoring is flying planes and measuring the sulphur dioxide, carbon dioxide and hydrogen sulfide. These three gases are measured because they’re the main gases that come off magma when it’s degassing. These will give us an indication of how close the magma is to the surface. We’ve been very busy recently, we had the two Tongariro eruptions so we’ve been doing lots of response flights. There’s a lot of ash around and quite a bit of gas coming out So we’re regularly monitoring Tongariro. Ruapehu is another one that we monitor on a regular basis, monthly. It has been a little bit restless so we’ve been doing a few response flights to that as well. We’re here at Taupo airport today we’re heading to White Island which showed signs of ash emissions on Saturday. This is a response flight, normally would fly every month but we’re doing a few extra ones because it’s shown signs of a little bit of activity The Plane’s been specially modified, we’ve got a special door that we bought, put a hole in it, and this enables us to put our equipment out the door. We have the COSPEC and the FLYSPEC which measure sulfur dioxide. These instruments look up and they measure concentration per metre. Three other instruments are bolted on in a special fashion. Approaching the island there’s a nice visible plume so it’ll make our measurement is quite easy. We fly in wind circles to measure the wind speed and wind direction. We fly with a neutral throttle which means it’s only the wind that determines how fast the plane is going. When we go against the wind, it slows us down, and thats our slowest speed, when we go with the wind it speeds us up, and that’s out fastest speed. So we can calculate the difference and calculate the wind speed. This is all done with A GPS which also gives us our wind direction. After we’ve done the wind circles the next thing is to fly as low as we can. 200 feet is as low as we’re allowed to fly. We fly at right angles to the wind under the plume. What we’ve got on the graph here is sulphur dioxide concentration as ppm, per metre. That gives us the concentration in the plume. we factor in the wind speed later. We fly backwards forwards and we do this seven or eight times. After we finish the transets for the sulphur dioxide measurements we have to do a contouring flight which means we have to fly through the plume collecting gas . As we go up it actually sucks gas in through the bottom of the plane into the instrument. At different altitudes, starting from below the plume where there’s nothing, hit the plume and climb 200 feet at intervals until we get to the top of the plume where we get no gas again. After we finish the gas measurements we go for a visual flight, take photos. We had a flight here a couple of weeks ago and it’s interesting to see the differences. What we can see today which is slightly different from two weeks ago is a vent with a tuff cone and a great big hole, and there’s gas coming out of that. It’s surrounded by a little lakelet, theres also quite a bit of colour brown round which probably indicates a bit of the ash that came out. There’s a lot of yellow colour in the crater which is elemental sulphur. The tuff cone that was created at the end of last year still seems to be there in it’s normal form, and there’s a little bit of dark discolouration in the plume. I have downloaded the data after coming back to the office and I’m starting to do the calculations. These are the sulphur dioxide pieces that we got from the COSPEC. You can see as we fly along out of the plume, hit the plume, come up, then down out of the plume, turn around and come backwards and forwards under the plume. We put these into a spreadsheet and we end up with a flux in tons per day. Today we got slightly over 600 tons per day which is very so much what we got two weeks ago and two weeks before that. So we’re not seeing any huge increases in gas so far in response to the ash eruption on the weekend. It’s no different from the previous flights and since the end of January.

 

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