The occurrence of groundmass crystals reveals the shallow conduit process of magmas, which affects the behavior of eruptions. Here, we analyzed groundmass microtextures of ash samples from the 2018 eruption of Shinmoedake volcano, Japan, to evaluate the change of magma ascent conditions during the eruption sequence. The eruptive activity changed from ash venting (Phase 1: March 1–6) to lava effusion with continuous ash-laden plumes (Phase 2: March 6–9) and then shifted to Vulcanian explosions (Phase 3: March 10–April 5). Non-juvenile particles were abundant in Phase 1, whereas juvenile particles were dominant in Phases 2 and 3. Vesicular juvenile particles were more abundant in Phase 2 than Phase 3. The lower microlite crystallinity and groundmass SiO₂ concentrations of the vesicular particles indicate that they were sourced from magma that ascended rapidly. Abundant nanolites were observed in the black interstitial glass of juvenile particles under an optical microscope, whereas few nanolites were observed in the transparent ones. The presence of nanolites can be explained by the dehydration of silicate melt, as well as cooling and oxidation between fragmentation and quenching. Temporal changes in the ash componentry show that the eruption activity started from the erosion of the pre-existing vent plug (Phase 1), shifted to the simultaneous eruption of bubble-bearing and outgassed magmas (Phase 2), and concluded with explosions of the stagnant lava (Phase 3), thereby demonstrating the sequence of vent opening and extrusion and stagnation of magma. Therefore, ash microtextures are valuable for monitoring the shallow conduit process of eruptive magma.

地基晶体的出现揭示了岩浆的浅层导管过程，这影响了火山喷发的行为。在这里，我们分析了日本Shinmoedake火山2018年喷发的灰烬样品的地面微观结构，以评估喷发过程中岩浆上升条件的变化。喷发活动从排灰（阶段1：3月1–6）转变为熔岩不断喷出烟灰（阶段2：3月6–9），然后转变为瓦肯火山爆发（阶段3：3月10日至4月5）。 。在阶段1中，非幼虫颗粒丰富，而在阶段2和3中，幼虫颗粒占主导地位。在阶段2中，相比于阶段3，囊状幼体颗粒更丰富。微晶的结晶度和底质SiO ₂较低。囊泡颗粒的浓度表明它们来自迅速上升的岩浆。在光学显微镜下，在黑色粒子的黑色间隙玻璃中观察到大量的纳米晶，而在透明的纳米晶中观察到的纳米晶很少。纳米晶的存在可以通过硅酸盐熔体的脱水以及在断裂和淬灭之间的冷却和氧化来解释。灰分成分的时间变化表明，喷发活动从预先存在的排气塞的侵蚀开始（阶段1），转移到同时冒泡的岩浆和脱气的岩浆（阶段2），并以喷发的爆炸结束。停滞的熔岩（第3阶段），从而展示了喷口打开，喷出和岩浆停滞的顺序。所以，