Teacher resources and professional development across the curriculum
Teacher professional development and classroom resources across the curriculum
|More About FORECASTING
Let's take a closer look at how volcanologists use precursory phenomena such as seismicity, gas emissions, and ground deformation to forecast eruptions.
Volcanic seismicity has three major forms: short-period earthquakes, long-period earthquakes, and harmonic tremor. Short-period earthquakes are like normal fault-related earthquakes. They are related to the fracturing of brittle rock as the magma forces its way upward. These short-period earthquakes signify the growth of a magma body near the surface. Long-period earthquakes are believed to indicate increased gas pressure in a volcano's "plumbing system." They are similar to the clanging sometimes heard in your home's plumbing system. Harmonic tremor occurs when there is sustained movement of magma below the surface.
Patterns of seismicity are complex and often difficult to interpret. However, increasing activity is very worrisome, especially if long-period events become dominant and episodes of harmonic tremor appear.
On several occasions, such as before the Mt. Pinatubo eruption, sulfur dioxide emissions have dropped to low levels prior to eruptions. Most scientists believe that this drop in gas levels is caused by the sealing of gas passages by hardened magma. Such an event leads to increased pressure in the volcano's plumbing system and an increased chance of an explosive eruption.
"Volcanoes" is inspired by programs from Earth Revealed.