Many explosive volcanic eruptions produce underexpanded starting gas-particle jets. The dynamics of the accompanying pyroclast ejection can be affected by several parameters, including magma texture, gas overpressure, erupted volume and geometry. With respect to the latter, volcanic craters and vents are often highly asymmetrical. Here, we experimentally evaluate the effect of vent asymmetry on gas expansion behaviour and gas jet dynamics directly above the vent. The vent geometries chosen for this study are based on field observations. The novel element of the vent geometry investigated herein is an inclined exit plane (5, 15, 30° slant angle) in combination with cylindrical and diverging inner geometries. In a vertical setup, these modifications yield both laterally variable spreading angles as well as a diversion of the jets, where inner geometry (cylindrical/diverging) controls the direction of the inclination. Both the spreading angle and the inclination of the jet are highly sensitive to reservoir (conduit) pressure and slant angle. Increasing starting reservoir pressure and slant angle yield (1) a maximum spreading angle (up to 62°) and (2) a maximum jet inclination for cylindrical vents (up to 13°). Our experiments thus constrain geometric contributions to the mechanisms controlling eruption jet dynamics with implications for the generation of asymmetrical distributions of proximal hazards around volcanic vents.

中文翻译：

---

来自复杂喷口的超压气体的释放特性：对火山灾害的影响

许多爆炸性火山喷发会产生膨胀不足的起始气体粒子射流。伴随的火山碎屑喷射的动力学可能受到几个参数的影响，包括岩浆质地、气体超压、喷发体积和几何形状。对于后者，火山口和火山口通常高度不对称。在这里，我们通过实验评估了排气口不对称对排气口正上方的气体膨胀行为和气体射流动力学的影响。本研究选择的喷口几何形状基于实地观察。此处研究的通风口几何形状的新颖元素是倾斜的出口平面（5、15、30° 倾斜角）与圆柱形和发散的内部几何形状相结合。在垂直设置中，这些修改产生横向可变的扩散角以及射流的分流，其中内部几何形状（圆柱形/发散）控制倾斜的方向。射流的扩散角和倾角都对储层（导管）压力和倾斜角高度敏感。增加起始储层压力和倾斜角产生 (1) 最大张开角（高达 62°）和 (2) 圆柱形通风口的最大射流倾角（高达 13°）。因此，我们的实验限制了对控制喷发射流动力学机制的几何贡献，这对火山喷口周围近端灾害的不对称分布的产生有影响。增加起始储层压力和倾斜角产生 (1) 最大张开角（高达 62°）和 (2) 圆柱形通风口的最大射流倾角（高达 13°）。因此，我们的实验限制了对控制喷发射流动力学机制的几何贡献，这对火山喷口周围近端灾害的不对称分布的产生有影响。增加起始储层压力和倾斜角产生 (1) 最大张开角（高达 62°）和 (2) 圆柱形通风口的最大射流倾角（高达 13°）。因此，我们的实验限制了对控制喷发射流动力学机制的几何贡献，这对火山喷口周围近端灾害的不对称分布的产生有影响。