An analytical model for gas overpressure in slug-driven explosions: Insights into Strombolian volcanic eruptions
An analytical model for gas overpressure in slug-driven explosions: Insights into Strombolian volcanic eruptions
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DOI：
10.1029/2011jb008747
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发表时间：
2012-02-10
影响因子：
3.9
通讯作者：
Lane, Steve J.
中科院分区：
文献类型：
--
作者：
Del Bello, Elisabetta;Llewellin, Edward W.;Lane, Steve J.
斯特龙博利式火山喷发在玄武岩火山中很常见，是一种温和的爆炸事件，由一个大的岩浆气体气泡（一个鼻涕虫）沿着管道上升并在表面破裂所驱动。爆破段塞中的气体超压控制着爆炸动力学和爆炸活力，是控制相关声震信号的主要因素。我们提出了一个基于岩浆静态和几何考虑的段塞超压的理论研究，并开发了一组方程，可用于计算段塞爆炸时的超压，段塞长度，以及爆炸过程开始的深度。我们发现，爆发超压是由两个无量纲参数：V '，这代表的气体在段塞的量，和A'，这代表的厚度的岩浆，福尔斯周围的上升段塞下降。爆炸超压随V'和A'的增加而非线性增加。我们考虑两个喷发的情况：（1）“标准模型”，其中岩浆仍然局限于喷口在段塞膨胀，和（2）“溢出模型”，其中段塞膨胀与熔岩渗出，偶尔在现场观察到。我们发现，段塞超压是较高的溢流模型的1.2-2.4倍。将我们的模型应用于斯特龙博利典型的斯特龙博利喷发，我们发现，对于体积>24-230 m3的段塞，从被动脱气到爆炸性爆发的转变发生，取决于岩浆粘度和管道直径，在爆发时，典型的Strombolian段塞（体积为100-1000 m3）具有1-5巴的内部气压和13-120 m的长度。我们比较模型的预测与现场数据从斯特龙博利低能量的“吹牛者”，温和的爆炸性斯特龙博利火山爆发，猛烈爆炸2003年4月5日发作。我们发现，模型的预测是一致的，在这一广泛的喷发风格的现场观察，提出了一个共同的蛞蝓驱动的机制，我们建议，突发事件是由异常大的蛞蝓（大V '）。
Strombolian eruptions, common at basaltic volcanoes, are mildly explosive events that are driven by a large bubble of magmatic gas (a slug) rising up the conduit and bursting at the surface. Gas overpressure within the bursting slug governs explosion dynamics and vigor and is the main factor controlling associated acoustic and seismic signals. We present a theoretical investigation of slug overpressure based on magma-static and geometric considerations and develop a set of equations that can be used to calculate the overpressure in a slug when it bursts, slug length at burst, and the depth at which the burst process begins. We find that burst overpressure is controlled by two dimensionless parameters: V', which represents the amount of gas in the slug, and A', which represents the thickness of the film of magma that falls around the rising slug. Burst overpressure increases nonlinearly as V' and A' increase. We consider two eruptive scenarios: (1) the "standard model," in which magma remains confined to the vent during slug expansion, and (2) the " overflow model," in which slug expansion is associated with lava effusion, as occasionally observed in the field. We find that slug overpressure is higher for the overflow model by a factor of 1.2-2.4. Applying our model to typical Strombolian eruptions at Stromboli, we find that the transition from passive degassing to explosive bursting occurs for slugs with volume >24-230 m(3), depending on magma viscosity and conduit diameter, and that at burst, a typical Strombolian slug (with a volume of 100-1000 m(3)) has an internal gas pressure of 1-5 bars and a length of 13-120 m. We compare model predictions with field data from Stromboli for low-energy " puffers," mildly explosive Strombolian eruptions, and the violently explosive 5 April 2003 paroxysm. We find that model predictions are consistent with field observations across this broad spectrum of eruptive styles, suggesting a common slug-driven mechanism; we propose that paroxysms are driven by unusually large slugs (large V').