Magma degassing during the Plinian eruption of Novarupta, Alaska, 1912

摘要: [1] We have modeled the nucleation and isothermal growth of bubbles in dacite from 1912 Plinian eruption Novarupta, Alaska. Bubble calculations account for exsolution H2O CO2, beginning with bubble ending when sizes reproduced observed size distribution vesicles Novarupta pumice clasts. Assuming classical theory, nucleated a diameter order 10−8 m grew to ranging 10−6 greater than 10−3 m, typical range vesicle found pumice. The smallest pumices are also most abundant radii 10−5 comprise almost 90% entire population. We find that these must grown their final within few 100 milliseconds. Despite extremely fast rates, pressures exsolved volatiles contained remained high, up about 107Pa excess ambient pressure. closed-system, potential energy compressed was sufficient cause magma fragmentation, even though only fraction pre-eruptive had exsolved. Unless matrix glasses pyroclasts retains large volatiles, majority magmatic (80–90%) likely lost by open-system degassing between fragmentation quenching.