How exactly can you predict volcanic eruptions?

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Volcanology: Monitoring and prediction of volcanic eruptions

As the earth's population grows, the pressure to populate volcanically active areas is increasing. Two million people live in the immediate vicinity of Pinatubo in the Philippines alone. In addition, volcanic soils are rich in minerals and therefore very fertile. In future volcanic eruptions, more and more people will be affected. In order to keep the number of victims and damage as low as possible in the event of an outbreak, precise predictions about the timing, type and strength of eruptions are becoming more and more necessary.
In order to be able to make such predictions, scientists need basic information about volcanic mechanisms as well as about the historical behavior of a volcano. For this purpose, the deposits of previous eruptions are examined. The amount, composition, age and the type of deposit provide initial clues about the behavior of the volcano. However, it is not yet possible to make precise predictions on the basis of statistics.
Then there is the monitoring, the constant surveillance of the volcano. If the volcano researchers work on site, the technical equipment is of immense importance. In Hawaii, for example, there has been a research station on the rim of the crater since the beginning of the 20th century. From here the volcano is monitored with the most modern computer technology. Data from seismographs, rain gauges, surveillance cameras and GPS receivers are collected and evaluated. Special work clothing is only required when the volcanologists approach an eruption center. That working on the volcanoes is dangerous is also shown by the fact that researchers repeatedly die in the process. So were the great eruption of Mount. St. Helens also included several geologists among the victims.
In general, volcanologists pay attention to important changes that occur when the magma rises before an eruption. In detail these are:

  • Volcanic earthquakes
  • Expansion of magma chambers
  • Increased degassing and changed gas composition
  • Heating up


  • Volcanic earthquakes

    Ever since humans have observed volcanoes, intensified earthquake activity has been detected in advance of all eruptions under and in the immediate vicinity of the volcano. The earthquakes can be observed with the help of seismic measurements. For this purpose, seismometers are installed on the volcano. These are instruments that can measure the finest floor vibrations.
    Around 200 active volcanoes are seismically monitored. With a high density of measuring stations, it is now possible to localize the earthquakes with an accuracy of 100 m.

    Pictures of volcano observation


    The movements of magma and hydrothermal fluids in the area of ​​active volcanoes generate a wide range of different seismic signals. They are triggered by the opening of ascent routes, the movement of magma along old fracture surfaces and the transport of fluids.
    Seismic monitoring can therefore provide a glimpse into the dynamic processes inside a volcano.
    Perhaps the most distinctive property of slow shear waves is that they cannot reproduce in liquids. Therefore, they are used specifically for finding magma chambers. But also the type, frequency and intensity of a volcanic quake allow conclusions to be drawn about the processes in the earth's interior.
    In order to predict a volcanic eruption, it is necessary to know the exact seismicity in an area so that the various earthquakes can be correctly assigned to a volcanic event. Years of observation are necessary for this. In the past, based on the events observed, a sequence of volcanic earthquakes has crystallized, which mostly precedes a volcanic eruption.

    1. High frequency earthquake
    2. Low frequency earthquakes
    3. Harmonic tremors (tremors)
    4. Eruption

    High-frequency earthquakes occurring in swarms are caused by brittle fractures in the rock. They are created under the pressure of the magma that is trying to find its way to the surface. Depending on the distance the magma travels, this type of tremor can last for a long time and does not necessarily have to result in a volcanic eruption.
    When the magma reaches depths of 3 km, it begins to degas under the weakening pressure. Gas bubbles form, which make it difficult for the magma to flow. The consequence is a lower speed of the earthquake waves. So low-frequency quakes indicate what is happening in liquids.
    The harmonic tremors, also called tremors, are very characteristic. They are characterized by very constant amplitudes and frequencies. These tremors can last for hours or even days. Since they occur at depths of 2 - 4 km and often just before the eruption, they are interpreted as turbulent movements of the rising magma column.

    Pictures of volcano observation


    Expansion of magma chambers

    Observing soil deformation is also important for monitoring volcanoes. If magma rises and collects inside the volcano, the mountain gradually swells. The result is that its surface expands.
    Cracks appear, inclinations and distances change. In order to track down these changes, inclination and distance measurements are necessary. Precise monitoring techniques are used for this today. Distances are measured with an electronic distance meter, or EDM for short, to the millimeter. The device sends electromagnetic signals that are reflected from a targeted object and received again in the EDM. The distance can be determined based on the phase shift of the received signal. Comparative measurements provide information about the development.
    In recent years, however, the GPS satellite measuring system has been increasingly used for distance measurements.

    Volcanic gases

    The amount and composition of the escaping gases is another indicator of an impending volcanic eruption. The gases dissolved in the magma are released into the atmosphere via fumaroles, cracks and active craters. But their mere presence does not say anything about impending outbreaks. Stagnant magma bodies in the crust also release gases. Significant changes in the gas composition are important. In the past, strongly increased SO2 emissions were often observed some time before volcanic eruptions.
    Different methods are used to determine the gas composition. The direct taking of gas samples is the most precise and also the most dangerous option, as the researchers have to dare to get very close to the active areas. The gases are withdrawn directly at the gas outlets. The volatile substances are led into glass flasks filled with analysis solution, collected and later examined in the laboratory. Unfortunately, this method only provides a snapshot. It is known from continuous measurements that gas compositions can change very quickly.
    Continuous measurements of the gas composition on site are best. It is technically much more complex, but delivers fully automatic results seamlessly and in real time.
    The measurement of volcanic gases is carried out remotely with a gas spectrometer, the so-called COSPEC. The volcano researcher couple Katja and Maurice Krafft played a key role in the development of these portable devices.
    Satellite systems can also be used to measure gas during larger outbreaks.

    Pictures of volcano observation

    Thermal image of a lava flow


    Heating up

    Imminent volcanic eruptions can also be tracked down with simple temperature measurements. Because rising magma heats the surrounding rock. The soil temperature, but also the temperatures of fumaroles, water sources and crater lakes rise. This also leads to sudden snowmelts.
    The temperatures are measured on a small scale with temperature probes. Thermal imaging cameras also provide valuable services here, but do not deliver the most precise results. In the context of remote sensing, more and more infrared images are being made from satellites. These usually record large-scale structures and do not provide absolute values, only temperature ranges.

    On their own, all of the described observation methods are not meaningful enough to make predictions about the behavior of a volcano. Only in their entirety is there enough data to be able to make relevant statements. However, there is still a long way to go scientifically to predict a volcanic eruption precisely. There is still too little knowledge about the eruption mechanisms, which differ from volcano to volcano. It is particularly difficult to collect enough reference values ​​for volcanoes that erupt very rarely. Most volcanologists today know about an impending volcanic eruption, but can only rarely predict the exact time when an eruption will begin.

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