Sector collapse

A sector collapse or lateral collapse is the structural failure and subsequent collapse of part of a volcano. Unlike a flank collapse, a sector collapse involves the central volcanic pipe. Sector collapses are one of the most hazardous volcanic events, often resulting in lateral blasts, landslides, and changes in volcanic eruptive behavior. Sector collapse can be caused by earthquakes, volcanic eruptions, gradual volcanic deformation, and other processes. Sector collapse events can occur on volcanoes present at both convergent and divergent plate boundaries. Sector collapses are generally very sudden; however, some attempts have been made to predict collapse events. Sector collapse can result from internal volcanic processes. Volcanic eruption can damage originally stable magma chambers, causing a portion of the volcano to collapse. While eruption is one cause, sector collapse can occur without any eruption. Magmatic intrusions can also lead to sector collapse. Dikes fracture and deform rock, leaving the volcano weaker and more susceptible to collapse. Hydrothermal activity is another internal cause, likely due to reactions of acid-sulfates weakening volcanic rock. Gravity-induced collapse occurs when the volcanic slope approaches the critical angle of repose. The slope angle is a major factor in collapse events. Sector collapse sometimes occurs because of external processes. Seismic activity is a prominent cause of collapse events. Earthquakes can weaken the structural stability of volcanoes, leading to sudden collapse or contributing to a later collapse. Intense weather and heavy rainfall can cause damaging erosion, increasing likelihood of collapse. Glacial melting is another external cause of sector collapse, with the majority of glacial melt induced collapses occurring during the Pleistocene. Glacial melting increases volcanic slope and decreases pore pressure, leading to sector collapse. Sea level change has also been associated with sector collapse. Because sector collapse events occur suddenly and over small time periods, they are difficult to predict.