A CT scan for a volcano
Scientists have created a detailed picture of the plumbing system beneath Mount Vesuvius using a technique called seismic tomography. This method works much like a medical CT scan but uses seismic waves to see through rock. By recording the travel times of waves from micro-earthquakes and controlled explosions, researchers can map out areas where the waves speed up or slow down. These velocity changes reveal the structure deep inside the volcano.
A major research effort, the TomoVes project, found a high-velocity body extending vertically from about 400 meters below the crater down to at least 3 kilometers. This is interpreted as the solidified remnants of magma from past eruptions, forming a rigid central conduit. Deeper still, seismic models show evidence of a low-velocity zone at a depth of about 8 to 10 kilometers. This zone, covering an area of at least 400 square kilometers, is thought to be an extensive, sill-like magma chamber where partially molten rock is currently stored. This deep reservoir is large enough to fuel future explosive eruptions. There is no evidence for a large magma chamber at depths shallower than 8 km.