Scanning the plumbing systems of volcanoes
One of the most powerful tools for imaging the roots of active volcanoes is seismic tomography which is similar to a common x-ray scan but it uses seismic waves instead of x-rays and is applied on a much grander scale. Seismic waves are long-wavelength sound waves that travel through the rock layers. We can “listen” to the seismic waves with sensitive and precise instruments called seismometers.
From the recordings of the seismic waves, we measure the time of travel from the source (e.g., a hammer blow or an earthquake) to the seismometer. If we divide the length of the propagation path by the time of travel we can derive the average speed of the seismic wave along the path, this is called the seismic velocity. If we repeat this measurement for many sources and many receivers we can reconstruct the distribution of the seismic velocity in three-dimensions.
Scientists have developed many creative ways to use seismic waves to generate images of the subsurface. Many of these methods have been applied to imaging active volcanoes. At least 78 volcanoes have been imaged in this way.
Seismic waves move more slowly when they cross rocks that are hot or molten. If we detect a region that has an anomalously low seismic velocity it is likely that it may be a magma reservoir.
With this method, scientists have discovered and studied many magma reservoirs. Some are relatively small, only a few hundred of meters in thickness, like the one found under Kolumbo volcano in Greece. Others are enormous like the one found beneath Uturuncu volcano in the Andes, which is 10 km in thickness and 200 km in diameter.
In the following pages you will get to know some of the best studied magma plumbing systems across the World.