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Through Volcano, Geology and Volcanism

A volcanologist is a geologist who studies the eruptive activity and formation of volcanoes and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra (such as ash or pumice), rock and lava samples. One major focus of enquiry is the prediction of eruptions; there is currently no accurate way to do this, but predicting or forecasting eruptions, like predicting earthquakes, could save many lives.

Modern volcanology

In 1841, the first volcanological observatory, the Vesuvius Observatory, was founded in the Kingdom of the Two Sicilies. Volcanology advances have required more than just structured observation, and the science relies upon the understanding and integration of knowledge in many fields including geology, tectonics, physics, chemistry and mathematics, with many advances only being able to occur after the advance had occurred in another field of science. For example, the study of radioactivity only commenced in 1896, and its application to the theory of plate tectonics and radiometric dating took about 50 years after this. Many other developments in fluid dynamics, experimental physics and chemistry, techniques of mathematical modelling, instrumentation and in other sciences have been applied to volcanology since 1841.

Techniques

Seismic observations are made using seismographs deployed near volcanic areas, watching out for increased seismicity during volcanic events, in particular looking for long-period harmonic tremors, which signal magma movement through volcanic conduits.

Surface deformation monitoring includes the use of geodetic techniques such as leveling, tilt, strain, angle and distance measurements through tiltmeters, total stations and EDMs. This also includes GNSS observations and InSAR. Surface deformation indicates magma upwelling: increased magma supply produces bulges in the volcanic center's surface.

Gas emissions may be monitored with equipment including portable ultra-violet spectrometers (COSPEC, now superseded by the miniDOAS), which analyzes the presence of volcanic gases such as sulfur dioxide; or by infra-red spectroscopy (FTIR). Increased gas emissions, and more particularly changes in gas compositions, may signal an impending volcanic eruption.

Temperature changes are monitored using thermometers and observing changes in thermal properties of volcanic lakes and vents, which may indicate upcoming activity.

Satellites are widely used to monitor volcanoes, as they allow a large area to be monitored easily. They can measure the spread of an ash plume, such as the one from Eyjafjallajökull's 2010 eruption, as well as SO2 emissions. InSAR and thermal imaging can monitor large, scarcely populated areas where it would be too expensive to maintain instruments on the ground.

Other geophysical techniques (electrical, gravity and magnetic observations) include monitoring fluctuations and sudden change in resistivity, gravity anomalies or magnetic anomaly patterns that may indicate volcano-induced faulting and magma upwelling.

Stratigraphic analyses includes analyzing tephra and lava deposits and dating these to give volcano eruption patterns, with estimated cycles of intense activity and size of eruptions.

Compositional analysis has been very successful in the grouping of volcanoes by type, origin of magma, including matching of volcanoes to a mantle plume of a particular hotspot, mantle plume melting depths, the history of recycled subducted crust, matching of tephra deposits to each other and to volcanoes of origin, and the understanding the formation and evolution of magma reservoirs, an approach which has now been validated by real-time sampling.

Forecasting

Some of the techniques mentioned above, combined with modelling, have proved useful and successful in the forecasting of some eruptions, such as the evacuation of the locality around Mount Pinatubo in 1991 that may have saved 20,000 lives. Short-term forecasts tend to use seismic or multiple monitoring data with long-term forecasting involving the study of the previous history of local volcanism. However, eruption forecasting does not just involve predicting the next initial onset time of an eruption, as it might also address the size of a future eruption, and evolution of an eruption once it has begun.

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