Strombolian explosions 1. A large bubble breaking at the surface of a lava
Strombolian explosions 1. A large bubble breaking at the surface of a lava
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斯特龙博利式爆炸 1. 熔岩表面的大气泡破裂
DOI：
10.1029/96jb01178
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
G. Brandeis
中科院分区：
文献类型：
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作者：
S. Vergniolle;G. Brandeis
斯特龙博利活动由岩浆柱表面的大型超压气泡破裂引起的一系列爆炸组成。斯特龙博利已经测量了36次爆炸的声压。我们认为，声音是由气泡在破裂前的振动产生的。振荡是由气泡内部的初始超压驱动的，假设气泡最初处于静止状态，就在岩浆-空气界面下方。惯性效应使气泡超过其平衡半径。然后，由于气体的可压缩性，气泡会变得欠压并收缩。这些振荡只受到气泡上方岩浆层粘性效应的轻微抑制。由于岩浆层上不断发展的不稳定性导致气泡在最小半径附近破裂，气泡不能完成一个以上的振动周期。假设一个简单的几何结构，我们对这种振动进行建模，并通过将合成波形与测量的声压进行拟合来约束气泡的半径和长度以及初始超压。无论是频率、m60rad S-1，还是振幅，合成波形与观测波形都有很好的拟合度。初始气泡半径为m1米，长度在几米到几十米之间变化。从初始超压，约10Pa.我们计算出喷出物的最大径向速度m 30m S-1。我们的模型的数据和预测之间的总体上很好的一致性使我们认为，声学测量是理解喷发动力学的有力工具。
Strombolian activity consists of a series of explosions caused by the breaking of large overpressurized bubbles at the surface of the magma column. Acoustic pressure has been measured for 36 explosions at Stromboli. We propose that sound is generated by the vibration of the bubble before it bursts. Oscillations are driven by an initial overpressure inside the bubble, assumed to be initially at rest, just below the magma-air interface. Inertia effects cause the bubble to overshoot its equilibrium radius. Then the bubble becomes underpressurized and contracts because of gas compressibility. These oscillations are only slightly damped by viscous effects in the magma layer above the bubble. The bubble cannot complete more than one cycle of vibration because of instabilities developing on the magma layer that lead to its breaking, near the minimum radius. Assuming a simple geometry, we model this vibration and constrain the radius and length of the bubble and the initial overpressure by fitting a synthetic waveform to the measured acoustic pressure. The fit between synthetic and observed waveforms is very good, both for frequency, m 60 rad s -1, and amplitude. The initial bubble radius is m 1 m, and the length varies between several and a few tens of meters. From the initial overpressure, approximately 10 Pa, we calculate the maximum radial velocity of ejecta, m 30 m s -1. The generally good agreement between data and predictions of our model leads us to suggest that acoustic measurements are a powerful tool for the understanding of eruption dynamics.