Caldera collapse thresholds correlate with magma chamber dimensions.

Explosive caldera-forming eruptions eject voluminous magma during the gravitational collapse of the roof of the magma chamber. Caldera collapse is known to occur by rapid decompression of a magma chamber at shallow depth, however, the thresholds for magma chamber decompression that promotes caldera collapse have not been tested using examples from actual caldera-forming eruptions. Here, we investigated the processes of magma chamber decompression leading to caldera collapse using two natural examples from Aira and Kikai calderas in southwestern Japan.

Magmatic overpressures, volatile exsolution and potential explosivity of fissure eruptions inferred via dike aspect ratios.

Buoyant magmas abundant in exsolved volatiles (bubbles) drive the rapid upward-propagation of feeder dikes from magma chambers. The consequence of a feeder dike reaching the surface can result in an explosive volcanic eruption depending, partly, on the retention of volatiles. Therefore, timely detection of the vesicularity and overpressure of the magma during feeder dike ascent is critical for the prediction of the explosivity of any future eruption.

Shallow magma pre-charge during repeated Plinian eruptions at Sakurajima volcano.

Vigorous explosive eruptions that produce continuous high eruption plumes (Plinian eruptions) are generally assumed to tap a magma reservoir. The 1914 Plinian eruption at the Sakurajima volcano located on the Aira caldera rim is one such case, where the main magma reservoir was assumed to be located approximately 10 km beneath the caldera. However, we report that estimated magma storage depths immediately prior to the eruption were much shallower (0.