Montanaro Cristian, Scheu Bettina, Mayer Klaus, Orsi Giovanni, Moretti Roberto, Isaia Roberto, Dingwell Donald B
Department of Earth and Environmental Sciences Ludwig-Maximilians-Universität München Munich Germany.
Department of Earth, Environment, and Resources Sciences University Federico II of Napoli Naples Italy.
J Geophys Res Solid Earth. 2016 Nov;121(11):7996-8014. doi: 10.1002/2016JB013273. Epub 2016 Nov 25.
Steam-driven eruptions, both phreatic and hydrothermal, expel exclusively fragments of non-juvenile rocks disintegrated by the expansion of water as liquid or gas phase. As their violence is related to the magnitude of the decompression work that can be performed by fluid expansion, these eruptions may occur with variable degrees of explosivity. In this study we investigate the influence of liquid fraction and rock petrophysical properties on the steam-driven explosive energy. A series of fine-grained heterogeneous tuffs from the Campi Flegrei caldera were investigated for their petrophysical properties. The rapid depressurization of various amounts of liquid water within the rock pore space can yield highly variable fragmentation and ejection behaviors for the investigated tuffs. Our results suggest that the pore liquid fraction controls the stored explosive energy with an increasing liquid fraction within the pore space increasing the explosive energy. Overall, the energy released by steam flashing can be estimated to be 1 order of magnitude higher than for simple (Argon) gas expansion and may produce a higher amount of fine material even under partially saturated conditions. The energy surplus in the presence of steam flashing leads to a faster fragmentation with respect to gas expansion and to higher ejection velocities imparted to the fragmented particles. Moreover, weak and low permeability rocks yield a maximum fine fraction. Using experiments to unravel the energetics of steam-driven eruptions has yielded estimates for several parameters controlling their explosivity. These findings should be considered for both modeling and evaluation of the hazards associated with steam-driven eruptions.
蒸汽驱动的喷发，包括潜水式和热液式喷发，仅喷出因水以液相或气相膨胀而崩解的非新生岩石碎片。由于其剧烈程度与流体膨胀所能完成的减压功的大小有关，这些喷发可能以不同程度的爆炸性发生。在本研究中，我们调查了液体含量和岩石岩石物理性质对蒸汽驱动爆炸能量的影响。对来自坎皮佛莱格瑞火山口的一系列细粒非均质凝灰岩的岩石物理性质进行了研究。岩石孔隙空间内各种数量的液态水的快速减压会导致所研究凝灰岩产生高度可变的破碎和喷发行为。我们的结果表明，孔隙液体含量控制着储存的爆炸能量，孔隙空间内液体含量增加会增加爆炸能量。总体而言，蒸汽闪蒸释放的能量估计比简单（氩气）气体膨胀高1个数量级，即使在部分饱和条件下也可能产生更多的细颗粒物质。蒸汽闪蒸情况下的能量过剩导致相对于气体膨胀更快的破碎，并赋予破碎颗粒更高的喷发速度。此外，软弱和低渗透性岩石产生的细颗粒比例最大。通过实验揭示蒸汽驱动喷发的能量学，已经得到了控制其爆炸性的几个参数的估计值。在对蒸汽驱动喷发相关危害进行建模和评估时，应考虑这些发现。
