Fig. 2

Summary of volcanological phenomena associated with large-scale explosive eruptions and the methods used for their detection. (1) During the stable accumulation stage, detection of the magma chamber prior to eruption is crucial. Some geophysical explorations of massive liquid zones (potential magma chamber) can be useful. Geochemical and petrological investigations on the leaked materials (magma and gases) from the magma chamber also can be potential methods to monitor the state of magma chamber. (2) Diking from the activated magma chamber may cause “unrest” of the volcanic system. Detection of the ground deformation and seismic activities can detect the progress of diking from the magma chamber toward the ground surface. Geochemical investigations of fumarole gas and ground gas emission may be also useful. Eruption does not occur when the propagating dike is arrested within the host rock. (3) After onset of eruption, monitoring of the eruption cloud will be useful to detect the magma discharge rate. Syn-eruptive ground deformation also shows the deflation of magma chamber by magma extraction. Geochemical and petrological investigations on the erupted magma can provide direct information about the magma storage which is feeding the eruption. Many eruptions may stall by various factors and the system back to the previous state. (4) After the eruption reaches to climax eruption (VEI 6 or larger), rapid deflation of magma chamber results collapse of the roof of magma chamber which can be detected by geodetic data and seismic signals. Monitoring of the behavior of ignimbrite and co-ignimbrite ash fall by remote-sensing methods is useful for evaluating widespread impacts