Hi I'm Brad Scott, I'm the volcano surveillance coordinator for GNS Science. So I basically have the responsibility for monitoring the active volcanoes in New Zealand. In New Zealand we basically have three types of volcanoes. Our classical cone volcanoes like Egmont, Ngauruhoe, Ruepehu, White Island. They are what people perceive as a volcano - looks like a volcano with a crater at the top. Our other volcanoes are Calderas, and globally, we have some of the best examples, and these are the super volcanoes of the world. And our third type of volcano in New Zealand is our volcanic field. These are small volcanoes that only erupt once, and the best known example of those are in Auckland. So we have our three volcano types. Our cone volcanoes - our traditional looking volcanoes the characteristics of them, is they erupt frequently, they have lots and lots of small eruptions. For example, Ruapehu has been active for between 240,000 to 270,000 years. So every 5 to 10 years, there will be a small-scale eruption, every 40 to 50 years there will be a bit bigger eruption, but as volcanic eruptions go, they're still at the small end of the scale. One of the ways we differentiate volcanoes is by the size of their eruptions. So our cone volcanoes erupt up to 1/10th of a cubic kilometer of material. Our second style of volcanism in New Zealand are the Calderas. In contrast to the cones, these don't erupt very often -they erupt around every 1 or 2 thousand years, and every 50,000 or 100,000 years they have a really enormous eruption. But the magnitude of these eruptions are all large. They start off at about 1 cubic kilometer but typically average somewhere around 5 or 10 cubic kilometers, they can go up to 50, 100 or even 500 cubic kilometers material. The good news is these are really rare. Yes they are in geological record, but the chances of us experiencing one are very low, but still there some of the best examples of these eruptions are Rotorua basin -the whole basin of Rotorua is the caldera volcano, 15 - 20 kilometers in diameter. Taupo is another example, both filled up by lakes, they're big topographic depressions. Our third style of volcano is our volcanic fields. Our best example is in Auckland, these are what we call mono genetic volcanism. This is where the volcano erupts once. So the volcano comes into eruption and builds a small volcanic cone, there’s some ash fall, some lava flows, and there’s some blasts, etc around the volcano, and then the volcano just quietens down, dies away, and the next eruption is in a totally new location. We have volcanic fields in Auckland, in Whangarei, and in the Bay of Islands. We've got these three different types of volcano in New Zealand but generically they're all similar in the way they work. The way we monitor a volcano is based on how the volcano works. So we have hot molten material at depth underneath the volcano - that is the heat source. As that material moves into the volcano to a shallower depth, or the volume changes, it has to create space for itself. So it may my break some rocks around it, and that will generate earthquakes. As the molten material moves it makes a noise with gas bubbles expanding and collapsing, and we can see that on our seismographs. That's by far our best tool for monitoring the volcanoes as it comes closer to the surface, it's going to start changing the shape of the ground surface and we'll get ground deformation. The ground may bulge up, so we look at geodesyor measuring the shape of the ground, and there we use a variety of techniques. It might be traditional surveying, leveling or triangulation, and more recently we're using GPS technology to give us real time record of how the ground is changing shape. That hot material also comes into contact with our groundwater system, and that generates our geothermal systems. So then we start looking at the chemistry of the hot water around the volcano, and the gasses associated with it. So although it doesn't matter whether it's a coneor a caldera or a volcanic field, the properties of how the volcano works are all very similar, and so our volcano monitoring program is based around looking at the three things -the seismicity, the geodesy or ground deformation, and water and gas chemistry.
Source:
0 comments:
Post a Comment