Volcanoes are some of the most complex systems on Earth. Volcanologists have always been challenged by the complexity and uncertainties associated with monitoring volcanic processes. However, advancements in technology have allowed volcanologists to develop new and reliable techniques for studying the many unique processes associated with volcanic activity.
Currently, geologists and volcanologists implement four different strategies for monitoring active or inactive volcanoes. They are:
- Hydrological studies
- Ground deformation measurements
- Seismic surveys
- Gas emission studies
Hydrology
Monitoring the hydrological processes associated with volcanic activity is important for understanding lahars (volcanic mudflows) and phreatomagmatic explosions – explosions that occur when ground water comes into contact with magma.
Lahars flow down existing drainages coming off the volcano, so understanding how water flows down these drainages is critical for understanding how lahars will flow down them. Hydrologists, geologists and volcanologists all collaborate on these kinds of studies to forecast where and with what speed a lahar will flow should one be produced. Likewise, understanding the ground-water processes below an active volcano can help in mitigating disasters that may result from an unexpected phreatomagmatic explosion.
Ground Deformation
When magma rises through the Earth’s crust and into a volcano’s conduit, it places a huge amount of pressure on the surrounding volcano’s slopes. In many cases, the slopes of the volcano will inflate and deflate with increasing and decreasing magmatic pressure. This process, known as ground deformation, can be monitored using a variety of instruments.
A popular instrument that has long been used to detect changes in the slopes of volcanoes is called a tiltmeter. Similarly to how a carpenter’s level works, a tiltmeter is placed on the slope of a volcano and a small container filled with fluid measures how much the tilt of the slope changes. The tiltmeter is hooked up to computers that show volcanologists by how much and in what direction the slope of a volcano is changing.
More recently, satellites have been used to monitor changes in slope. For example, Global Positioning System (GPS) instruments have been installed on volcanoes and linked to satellites orbiting our planet. When a volcano deforms, the changes in position of these GPS instruments is detected by the satellites and the exact amount and direction of movement can be calculated.
Seismic
Measuring the seismic activity at volcanoes is one of the oldest and most commonly used method to monitor volcanoes. As magma rises it breaks through rock and pushes on the slopes of the volcano causing seismic waves which we know as earthquakes. Most active volcanoes produce small earthquakes many times throughout the day. Volcanologists know these types of seismic signals and are not alarmed by them.
However, when seismic surveys detect a change in the seismic signals – such as an increase in magnitude or frequency – it is a red-flag to volcanologists that the volcano is becoming more active. Many volcano observatories now have automated seismic systems, so that when a large change is detected, volcanologists are automatically warned through alarms; instead of having to sit and watch seismic equipment all day and night to look for changes.
Gas Emissions
Monitoring the gases emitted by a volcano is also a commonly used technique. As magma ascends, the decrease in pressure causes the release of a variety of magmatic gases. The two most commonly measured gases are sulfur dioxide and carbon dioxide. These gases can be measured using field-based methods, such as gas trapping techniques – where gases are pumped into a bottle and taken back to a lab for measurements – or with remotes sensing instruments such as satellites.
Source: U.S. Geological Survey
