Monitoring & Predicting Volcanic Eruptions

by Jared Lubben & Matt Rogers

View of Mauna Loa from Mauna Kea

For decades, geoscientists have been using new and interesting ways to monitor volcanic activity to not only help predict an eruption, but to determine the intensity of eruptions. This web page will focus on three main methods that are used most by volcanologists to monitor and predict volcanic activity. These three main methods include monitoring volcanic gasses, seismic waves and the use of tiltmeters.

Monitoring Volcanic Gasses

Scientists have long recognized that gasses dissolved in magma are the driving forces of volcanic eruptions. Gasses such as sulfur dioxide and water vapor escape when magma rises toward the surface, and when the magma cools and crystallizes below ground.

The primary objective for scientists is to determine changes in the release of certain gasses from the volcano. This is very difficult to do, direct sampling of the gas requires a visit to an active vent, usually high on the volcano's flank.

Three main methods are used to monitor volcanic gas

• Measuring gas emission rates in gas plumes- by measuring changes in emission rates, scientists can infer changes in the magma below.
  
• Direct gas sampling and laboratory analysis- This method gives explicit composition of the gasses, but no emission rates.
  
• Continuous on site monitoring- Use of sensors directly in the vent records changes in
  Emission rates and sends data directly to the observatory.

Emission of gasses from Kilauea Iki

Monitoring Seismic Activity

Moving magma and other volcanic fluids trigger earthquakes below the surface. When magma rises, pressure is exerted causing the volcano to swell. This increase in pressure causes rocks to break, triggering earthquakes. Seismic activity almost always increases before an eruption. Scientists work to detect subtle and significant variations in the magnitude of the activity to determine an eruption. Networks of seismometers, an instrument that measures ground vibrations caused by earthquakes, are needed to precisely monitor seismic activity. Presently, computers and technology have enabled scientists to locate earthquakes faster and more accurately.

This seismograph, found at the observatory, monitors the seismic activity at
three different volcanoes. (From left, Mauna Loa, Kilauea Iki, Pu'u O'o)

Tiltmeters

Diagram of the water-tube tiltmeter

When a volcanic eruption is imminent, the magma and gasses below the surface cause the volcano to swell. After the eruption, when the magma below the surface moves back down, the volcano will subside. Both of these movements are measured by geologists with a tiltmeter. When the volcano is swelling, the tiltmeter can measure exactly how much the slope of the volcano is tilting away from the center of uplift. Usually the movement of this swelling amounts to a fraction of a degree.

This is the most widely used instrument for measuring the ground movement of the volcano. A tiltmeter, much like a level, has a small container with conductivity fluid. In this fluid there is a bubble that measures a change in slope. Electrodes within the fluid and the bubble determine the bubble's position. As the bubble moves, voltage output from electrodes changes in a way that correlates to the amount of tilt picked up by the tiltmeter. The tilt is measured in microradians (0.00006 degrees). Different tiltmeters are also used depending upon the type of volcano, as well as the expected degree of tilt.

These three methods of predicting eruptions are the most common. However, geologists also use GPS (Global Positioning System), Satellites, and remote sensing data in the prediction of volcanic eruptions.

Highlights from the Trip

View of lava entering the ocean

View of lava entering the ocean

View of the illuminated steam cloud after nightfall

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This web page has been brought to you by Jared (left) and Matt