| Hydrology | Ground Deformation | Seismicity | Gas | Remote Sensing |
| ... | |
| The ground around and under a volcano changes because of the pressure of the magma under the ground. Earthquakes also happen often when a volcano is active and the ground shifts around when earthquakes hit. This is called volcano deformation. Volcanic deformation is measured by instruments called tiltmeters and Global Positioning Systems (GPS). The instrument that has helped the scientists see the land under and around the volcano has let the scientists see more information about how the land around a volcano changes more than ever before. | |
| Image from a GPS instrument |
 |
 |
Electronic
Distance Measurements
|
|
Tiltmeters |
 |
 |
Global
Positioning System
|