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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Delayed brittle-like fragmentation of vesicular magma analogue by decompression
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Delayed brittle-like fragmentation of vesicular magma analogue by decompression

机译：减压使囊状岩浆类似物延迟脆性破碎

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A rapid decompression experiment using syrup containing gas bubbles was conducted in order to clarify the fragmentation of vesicular magma, which is a key phenomenon in volcanic eruptions. We focus on brittle-like fragmentation, which occurs with a longer time scale than brittle fragmentation. The response of the bubbly syrup to the decompression for various viscosities and porosities was tested under various initial pressures, pressure differences, and decompression times. The response observed by high-speed photography was classified using the Deborah number DeDT, which is defined as the ratio of the viscoelastic relaxation time of the syrup to the decompression time, the maximum differential stress at the bubble surface △Ωmax, and a measure of instantaneous brittleness at the bubble surface ft at the time when the differential stress at the surface reaches the critical fracture stress △Ωc. In a number of the experimental runs in which both DeDT and ft indicated ductile response of the material, brittle-like fragmentation occurred when △Ωmax substantially exceeded △Ωc. For all of the runs in which brittle-like fragmentation was observed, the onset of fragmentation was delayed substantially from the relaxation time, whereas the onset occurred within the characteristic time for viscous expansion of the bubbles. In many cases of brittle-like fragmentation, fragmentation continued after the onset triggered by a single decompression event. Detailed analysis indicates that brittle-like fragmentation started with a sudden release of the gas in the bubbly syrup through a surface crack, which might lead to an increase in local brittleness. Magma fragmentation may be viewed as sequential brittle-like fragmentation. This view may provide an explanation for the observed time delay for the onset of an explosive eruption after a triggering decompression event.
机译：为了澄清囊状岩浆的破裂，进行了使用含有气泡的糖浆的快速减压实验，这是火山喷发的关键现象。我们专注于脆性碎片，这种碎片发生的时间要比脆性碎片更长。在各种初始压力，压力差和减压时间下，测试了各种不同粘度和孔隙率的气泡状糖浆对减压的响应。使用Deborah数DeDT对高速摄影观察到的响应进行分类，Deborah数定义为糖浆的粘弹性松弛时间与减压时间之比，气泡表面的最大压差△Ωmax和测量值。当气泡表面的微分应力达到临界断裂应力△Ωc时，气泡表面ft的瞬时脆性。在许多DeDT和ft都表明材料具有延性响应的实验运行中，当△Ωmax大大超过△Ωc时，发生了脆性碎裂。对于观察到脆性碎裂的所有运行，碎裂的发生均从松弛时间开始被延迟，而碎裂的发生发生在气泡的粘性膨胀的特征时间内。在许多类似脆性碎裂的情况下，碎裂在一次减压事件触发后继续发生。详细的分析表明，类似脆性的碎裂始于气泡糖浆中的气体通过表面裂纹的突然释放，这可能导致局部脆性增加。岩浆碎裂可以看作是连续的脆性碎裂。该视图可以为触发减压事件后爆炸爆发的观察到的时间延迟提供解释。

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