| Hydrology | Ground Deformation | Seismicity | Gas | Remote Sensing |
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| Scientists plant a network of seismometers around a volcano so that they can monitor earthquakes. | ||
| Before a volcano erupts earthquakes happen more often. Hundreds of earthquakes occur when a volcano is about to erupt. That is because magma and gasses are being pushed up toward the surface of the earth. Pressure inside the volcano increases because the rocks under the volcano are being broken and moved around. Volcanic earthquakes are not usually very strong and mostly measure about a 2 or 3 on the Ricter Scale. | ||
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