How many volcanoes are monitored

The USGS Volcano Hazards Prgram notes that the key to an accurate short-term eruption forecast is being able to recognize when such monitored data show consistent changes from normal background levels of activity. Monitoring-based forecasts are becoming much more reliable, but they remain imperfect.

If scientists are fortunate, precursors to an eruption follow the same course as they followed before previous eruptions. Patterns often change, though, and wholly new behavior is observed.

The best forecasts will be based on an integration of geologic history, realtime monitoring, and a deep understanding of the internal plumbing processes of the specific volcano. Even with the best of monitoring and interpretations, reliable forecasts are rarely possible more than a few days in advance of an eruption. Some forecasts of volcanic eruptions are based on eruption recurrence intervals, but these are notoriously unreliable for two reasons: 1 few volcanoes are sufficiently well studied to provide an accurate eruptive history over the many hundreds, or tens of thousands, of years necessary to establish a reliable recurrence interval; and 2 few volcanoes maintain the same behavior for long more often than not, as soon as a repetitive pattern becomes apparent, the volcano changes behavior.

Volcano observatories make forecasts with great caution as they can have huge impacts on the affected populations, in some cases forcing people to leave behind homes, farms, and livestock. Reliable forecasts, however, can be made by volcano observatory staff, who have the experience to interpret their monitoring that detects eruption precursors.

In , scientists studying the Tolbachik volcano in Russia saw a similar explosion as lava advanced over very thick snow. Luckily, they too were not hurt. But it is unlikely that these incidents can be easily forecast - either from the ground using instruments or from space. Dr Puglisi said: "It's not very easy to predict phreatic explosions.

The mechanism occurs very fast. The explosion is caused by the almost instantaneous evaporation of vapour, usually in small areas. These phenomena are usually relatively shallow and, in some cases, practically at the surface.

So this doesn't produce significant changes detected by monitoring systems. And in space, the resolution is not suitable to detect such phenomena. There is relatively little video footage of phreatic explosions and so the BBC film, captured by camerawoman Rachel Price, will be of interest to scientists as they try to learn more about these incidents. Key to the space monitoring project is the capability offered by the European Union's new Sentinel-1 radar satellites.

This pair of platforms repeatedly and frequently image the entire land surface of the globe, throwing their data to Earth using a high-speed laser link. By comparing a sequence of Sentinel pictures, in a technique known as interferometry, COMET's computing facility can track really quite small changes in the behaviour of a volcano, on the order of just millimetres the movements that might be most concerning would in all probability be much larger and even easier to sense.

But it's really only been used in the past retroactively, to try to understand what happened at a volcano after it erupted," explained Prof Hooper. What do radar satellites see when they look at volcanoes? The 1, figure is the number of land volcanoes that are known to have erupted at some point in the last 12, years more volcanoes exist under the sea but cannot be seen from space.

Many will appear long dormant, but every two years or so there is an event on a volcano that has no previous mention in the written records of having erupted. And in some parts of Africa, these records can start as recently as the 19th Century. One of the big research questions for scientists is working out if and when a change in the shape of a volcano will lead to an eruption. It can be a long time between the two, perhaps years. But the statistics suggest it is four times more likely that a volcano that deforms will erupt than one that has not changed its shape.

The aim is to have the satellite data on all 1, volcanoes being gathered and processed by the end of Etna escape: 'Pelted with deadly, hot debris'. BBC team 'shaken' after Mt Etna blast. Mapping Earth's slow surface warping. Geological Survey report. About one-third of the active volcanoes in the U. In , volcanic gas killed more than 1, people in Cameroon. And one of the latest theories about the epic eruption at Pompeii, in 79 A. But many volcanoes in the Cascades have only a couple of far-field sensors, several geologists told me.

The Pacific Northwest, which includes high-population areas in close proximity to active volcanoes, is of particular concern for public safety.

Helens, in Washington, was only 37 years ago, and it took until the volcano became active again in to start a truly comprehensive monitoring. This kind of assumption is therefore very dangerous, because most of our volcanoes are not as intensively monitored as we think they are or as they should be. Geological Survey. GPS helps fill in some of the gaps. More data means a better opportunity to identify eruption warning signs, which Segall hopes could eventually make it possible to forecast volcanic activity the way we can predict severe weather like hurricanes.