A weekly feature provided by scientists at the Hawaiian Volcano Observatory. The shape of active volcanoes is constantly changing.
Large movements occur during dike intrusions, large earthquakes, or landslides.
Smaller movements occur as magma moves through the volcano's plumbing system or in response to gravity and other forces that slowly deform the volcanic pile. The small movements can be detected only with very sensitive instruments. For example, in order to track the slow filling or emptying of a summit magma chamber buried at a depth of several miles, we need surface measurements that are accurate to a fraction of an inch. Monitoring these movements is important because they provide us with clues about what is happening inside the volcano and where and when the volcano may erupt. Volcanologists use special GPS receivers and sophisticated computer programs to measure ground movements to an accuracy of a fraction of an inch.