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Photo of Richard Herd Richard Herd
Paradise Postponed

At the Montserrat Volcano Observatory, Richard Herd takes a close look at the volcano that buried much of this lush island and gives Frontiers viewers a first-hand report.

q Are you afraid when working around the volcano?

A 'Afraid' isn't really the right word. We treat the volcano with a lot of respect as it is very easy to get caught out. When you are working close to the lava dome there is often a lot of noise and crashes from rockfalls. These can be pretty startling. Sometimes you feel the earthquakes through your feet which is not pleasant. But we try to ensure maximum efficiency in the dangerous areas, which means flying in to the site, doing the job quickly and flying out again.

q If the volcano does erupt what is the evacuation plan?

A There are many different evacuation plans depending upon the level of activity and the numbers of people involved. For scientists working in the field, increased levels of activity usually mean we have to withdraw immediately. Evacuation plans for the population at large involve restricting their access to certain areas, so they are not exposed to the hazard. We cannot wait until the event has begun because the situations in which people get killed are usually very short bursts of activity, and there is no possibility of evacuating them in this time. There is a bigger plan should the volcano erupt much more violently to evacuate everyone apart from the essential services. The problem with this is to evacuate a few thousand people with a major, sustained explosion going off in the background is far from easy.

q Why do tremors or mini-earthquakes happen after a volcanic eruption?

A There are many sorts of earthquakes associated with volcanic activity. They are all due to shaking of the earth's surface can be due to an increase in pressure, cracking of rocks in the dome and the volcano, gas release through cracks and fractures, movement along faults, and by rocks avalanching from the dome surface. Often after a collapse of rock from the lava dome we have a period of tremor which may last from 30 minutes to several hours. This is associated with vigorous ash venting from the dome and the collapse area. We think that it is caused by exposing a lot of extremely hot rock, rich in gas to a low pressure. This makes the rock disintegrate into ash and produce an ashy plume and the characteristic tremor signal after the activity.

q How big is the volcano and how fast did it grow?

A The current height of the dome is about 1010 metres above sea level. At the moment the lava dome has stopped growing and its level of activity has declined. The maximum it ever reached was 1031 metres above sea level, although the area of dome containing this point collapsed in a big pyroclastic flow on July 3rd 1998. Before the eruption began the highest point on Montserrat was 914 metres above sea level.

q Why do some volcanoes produce lava when they erupt and others like the one on Montserrat produce the ash and gas mixture? Why is the pyroclastic flow more dangerous?

A Montserrat does produce lava - but it is very different from the lava you see in the spectacular flows on Hawaii and Iceland. Hawaii lavas are made of a basalt which is really quite runny. So the Hawaiian lavas can flow as coherent streams to great distances. If you were caught in a lava flow you would be killed, but most lavas move so slowly that you can walk away from them. The lava on Montserrat is called andesite and is much thicker and cannot flow away from the volcano. Instead it builds up as a huge mass - a lava dome. This is unstable and can collapse generating rock falls and pyroclastic flows. Pyroclastic flows move very fast - up to 80 metres per second and can cover huge areas, and you have no chance of escaping them.

q My question is about the rocks and the samples and the ash layers that your colleagues collect around the volcano. Where do they go for testing, how are they tested and what do you learn from them?

A The samples are usually divided into three 'splits' and sent for analysis to Bristol University in the UK, Brown University in the USA and one sample is kept at the MVO. The rock samples are analysed by X-ray techniques, and with an electron microprobe. These techniques allows us to determine the chemical make-up of the rock, of individual minerals grains and even of parts of the mineral grain. This has allowed the workers to look at the chemical evolution of the magma and to make estimates of how quickly the magma is ascending using an unstable mineral phase.

q Could you please explain how you use the GPS receivers that were mentioned in the show.

A What we want to determine is whether there are any movements or bulging of the flanks of the volcano. We set up a series of steel bolts in bedrock or concrete and occupy these as a GPS stations. What we actually do is set up a tripod over the bolt very precisely and place a GPS sensor on top of it. This allows us to determine the position of that bolts relative to all the others to within a few millimetres. If we repeat this over the weeks and months we see that some of the bolts show a movement relative to the others. Thus we can work out which parts of the volcano are deforming. At Montserrat we saw about 8cm of movement over one sector of the volcano in about 9 months. This may not sound a lot, but it is huge when you consider the volume of rock involved. Now that the eruption has declined, we are seeing greatly reduced rates of deformation.

q I read in the newspaper last weekend that scientists believed that the volcano is entering a period of "extended dormancy." Is this correct?

A Yes, it is entering a quiet period now. It stopped erupting in the middle of March this year. For the immediate few weeks you don't know if it is simply a lull in activity or whether it has actually stopped. Once you get more than three months or so from a period of activity, you can consider that the eruption has stopped. Further activity would therefore constitute a new eruption. We have still had pyroclastic flows, rock falls and earthquakes generated, but there is no indication of any new magma reaching the surface.

q Will people be allowed to go back into the exclusion zone? Will Plymouth ever be rebuilt (or excavated) or will the new capital be on the northern end of the island? I used to live on Montserrat and would like to visit there some day - will that ever be possible?

A People are allowed into the exclusion zone at certain times. Mainly to collect belongings from areas that aren't too dangerous. I don't think it would be wise to rebuild Plymouth. It was in a vulnerable place to begin with, and this eruption had proved that. The same thing could happen again. Most people live up in the north or along the west coast of the island. At the moment there isn't a clear capital town. You can certainly come to Montserrat now; in fact my parents were out here a few days ago.

q Is there anything that lava can't melt or flow through?

A The Montserrat lava erupts at about 825 centigrade. Hawaiian lavas erupt at about 1150 centigrade. Obviously these temperatures will melt snow and turn water into steam, but this makes the lava cool down quickly. Lava can in fact melt rocks already on the earth's surface. Some of my colleagues first observed this on a volcano in Tanzania where the erupting lava stream slowly cut a notch through the rock onto which it was erupting. The same thing has been seen on Hawaii. Rocks are pretty resistant though and generally the lava builds up and flows over them, without a huge amount of melting. When lava erupts onto soil, it burns the organic material in the soil to a inches or so in depth. This produces methane and other gases which can cause small explosions.

q Was any data about the explosion lost when the volcano erupted by the old observatory?

A No data has been lost at the observatory due to the volcano. We have lost equipment due to its activity though - seismometers, tiltmeters, extensometers, GPS receivers and reflectors have all been lost.

q Do you think volcanologists will ever be able to predict eruptions perfectly?

A No. That is the only thing we can say for sure. Volcanoes are incredibly, complex natural systems, and there all sorts of effects which interplay to control the eruption rate, the gas bubble content and so on. The physics of these interplaying effects is largely unknown. The best we can do is to monitor intensively, observe, follow all the changes and when necessary give a wide margin of error. Some things are fairly obvious though and although we can't say a certain event will happen at 10:35 tomorrow morning, we can say that it is likely to happen very soon. If it does happen these areas will be affected and if you are in that area when it occurs you will be killed. The areas that have been threatened by pyroclastic flows here have always been obvious and so there haven't been any surprises when large flows have developed and destroyed new areas.

q Do you think we will ever have the technology to prevent volcanoes from erupting?

A No. I don't think we can prevent them erupting. Lava flows can be diverted to an extent, mud flows can be controlled. For explosions you need to get under a strong roof. For ashfall you need to wear a mask so you don't inhale the dust. For pyroclastic flows and surges, you can do nothing really, other than make sure that you are not close to the volcano.

Richard Herd is also featured in Cool Careers in Science. Check it out!


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