Growth and potential collapse of the lava dome in Unzen volcano and the estimation on block-and-ash flows

摘要

Heisei lava dome was formed in Unzen volcano over the period from 1991 to 1995. The recent continuous observations have shown that the lava dome is still growing, which is a threat for the life of the nearby residents. How to estimate the range of collapse and potential block-and-ash flows is an urgent problem. Airborne laser scanning method is briefly introduced. We presented a division to separate the lava dome with 10 potential collapsed blocks and set some measuring points to observe the elevation change in each block. By analyzing the elevation decrease from 2003 to 2014, the potential collapsed blocks that experienced obvious changes were identified. With the evaluation of elevation changes by airborne laser data, the buried terrain of dome was reconstructed. The results show that the whole lava dome from lobe 1 to 11 may collapse, and the potential maximum volume of collapsed part is 1.46 x 10(7) m(3). If the collapsed part forms block-and-ash flow, the flow will arrive at the seaside in approximately 7 minutes according to the result of simulation. The flow could travel approximately 8.5 km, and the average velocity is approximately 20 m/s.