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

点击翻译按钮获取中文摘要

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.