Continued Studies of Rates of Magma Ascent, Degassing and Crystallization - Controls on Eruptive Processes

火山爆发可能是爆炸性的，也可能是喷涌式的，可能是持续性的，也可能是偶发性的。当岩浆向地球表面上升时，火山导管内发生的过程决定了喷发方式。特别重要的是岩浆减压后新阶段（气泡和晶体）的形成。在熔体中加入气泡或结晶会影响岩浆流动的能力，从而影响岩浆的持续上升。虽然在过去的十年中，气泡形成在驱动火山喷发中的作用一直是研究的焦点，但脱气诱导结晶的重要性尚未得到充分认识。我们最近的工作表明，岩浆在上升过程中结晶的程度是由岩浆的总体组成和岩浆上升的速度共同控制的。在这里，我们建议通过确定两个火山系统（阿拉斯加的奥古斯丁火山和意大利的维苏威火山）中同喷发脱气诱导结晶的成分控制来量化这一普遍观察结果。两座火山在一次喷发中产生一系列岩浆成分，因此可以直接比较在类似条件下不同岩浆对喷发的反应。

Cashman & Johnston9909507Volcanic eruptions may be explosive or effusive, sustained or episodic. Eruptive style is determined by processes that occur within volcanic conduits, as magma rises toward the Earth's surface. Of particular importance is the creation of new phases (bubbles and crystals) in response to magma decompression. The addition of either bubbles or crystals to a melt affects the ability of the magma to flow, and thus its continued ascent. While the role of vesiculation (bubble formation) in driving volcanic eruptions has been the focus of intense study over the past ten years, the importance of degassing-induced crystallization has not been fully appreciated. Our recent work suggests that the extent to which magmas crystallize during ascent is controlled by both the bulk composition of the magma and the rate of magma rise. Here we propose to quantify this general observation by determining compositional controls on syn-eruptive degassing-induced crystallization in two volcanic systems: Mt. Augustine, Alaska and Vesuvius, Italy. Both volcanoes produce a range of magma compositions during a single eruption, and thus allow direct comparison of the response of different magmas to eruption under similar conditions.