Techniques to predict volcanic eruptions
Changes in ground level:
Tilt meters have long been used to study active volcanoes by monitoring their changing shape and steepness before and during eruptions. When pressurised magma enters the magma chamber beneath a volcano, the ground is forced upward, causing the slopes of the volcano to tilt away from the centre of uplift. Before an eruption occurs, magma flows toward the surface, deflating the magma chamber and causing a reversal in the tilt directions. This characteristic behaviour, coupled with measurements of earthquake frequency and magnitude, several tilt meters may be placed around a volcanoes dome to accurately take measurements. They are mainly used successfully by volcanologists around the world to predict eruptions hours to days before the actual event.
Historical pattern of activity
The eruption recurrence interval is old historical data and records of geological information used by volcanlogists to predict and figure out the statistics of how often a volcano erupts and size of the eruption. Now we look at volcanic deposits around the volcano to determine their age, type (lava flows, mudflows, ash flows), size, and distance from the volcano. This data will help to determine if the volcano is active.
Recording historic eruptions and modern volcano-monitoring in themselves are insufficient to fully determine the characteristic behavior of a volcano, because a time record of such information, though perhaps long in human terms, is much too short in geologic terms to permit reliable predictions of possible future behavior. A comprehensive investigation of any volcano must also include the careful, systematic mapping of the nature, volume, and distribution of the products of prehistoric eruptions, as well as the determination of their ages by modern isotopic and other dating methods. Research on the volcano's geologic past extends the data base for refined estimates of the recurrence intervals of active versus dormant periods in the history of the volcano. With such information in hand, scientists can construct so-called "volcanic hazards" maps that show the zones of greatest risk around the volcano and that designate which zones are particularly susceptible to certain types of volcanic hazards (lava flows, ash fall, toxic gases, mudflows and associated flooding, etc.).
Gas measurements
Gas samples are collected from fumaroles and from active vents. The composition of the gas or a change in the rate of gas emission provides additional information on what is happening inside the volcano. Changes in fumaroles gas composition, or in the emission rate of SO2 and other gases, may be related to variation in magma supply rate, change in magma type, or modifications in the pathways of gas escape induced by magma movement.
Gas can also be observed by looking at the superheated steam which is produced at high temperatures; this usually is a good indication of activity prior to an eruption as a result of shallow water rich magma.
Seismic activity
As magma moves into the reservoir during inflation, it must make room for itself by rupturing or crowding aside the solidified lava that surrounds the reservoir. Such underground ruptures produced seismic waves that travel through the volcano and are recorded by a network of seismometers placed on the volcanoes surface. Ground motions sensed by the seismometer are converted into electronic signals, which are transmitted by radio and are recorded on seismographs located at the volcano observatory. The seismic data are analysed to determine the time, location, depth, and magnitude of the earthquakes. Mapping the earthquake activity allows scientists to track the subsurface movement of magma.
Magma movement and the onset of an eruption produce a distinctive seismic pattern called harmonic tremor. Seismologist must sort through the records of hundreds of earthquakes and determine which are related to the volcano and which were caused by man-induced or natural forces.
Cone temperature
Remote-sensing imagery from satellites can sometimes show up thermal anomalies near the cones of the volcanoes, caused when rising magma heats the rocks close to the surface on active vents, showing a clear increase in cone temperature prior to an eruption. Images shown by infrared heat sensors detected by the satellite send back images of even the slightest of temperature changes, which makes it a very reliable early warning system. Satellite surveillance offers some of the best future prospects for forecasting eruptions.
