Towards improved forecasting of volcanic explosivity: Investigating the role of magma mixing

世界上10%的人口居住在离火山100公里的范围内。随着世界人口的增长和对自然资源的压力，火山每天都威胁着更多的生命。火山爆发会对附近的居民造成毁灭性的社会影响，使整个国家被火山灰覆盖，毁坏庄稼和牲畜，并造成巨大的生命损失。这些喷发也会产生全球影响，有可能影响空中交通、空气质量和地表温度。相反，熔岩流或圆顶形成（喷涌）喷发通常危险性较小，其影响更局限于火山周围的区域。问题是，任何一座火山都可能以爆发性和喷涌性的方式喷发，并且喷发方式会迅速变化。我们目前还不清楚是什么控制了火山的喷发方式。我们知识上的这一空白使得即将到来的火山喷发的影响很难预测。例如，2010年冰岛埃亚菲亚德拉火山（Eyjafjallajokull）的喷发规模虽小，但破坏力极大，虽然火山学家可以预测几周内会发生喷发，但他们无法预测即将到来的喷发是爆发性的还是溢流性的。预测将发生何种类型的火山喷发以及火山喷发规模的能力将有助于通过通知疏散等缓解程序来限制人员生命损失并减少经济影响。不幸的是，在我们确定是什么控制了火山喷发的“爆炸潜力”之前，这一目标无法实现。大多数研究认为，在管道（岩浆给水管）内的浅层过程（<3公里）控制了这种转变，然而最近的工作表明，在岩浆储存（岩浆房内）时发生的深层过程（4-10公里）可能是关键。一个特别重要的过程是两个温度和化学成分不同的岩浆在深处混合，这通常发生在喷发前。岩浆中溶解的气体在这个过程中起着很大的作用，就像打开一瓶摇晃过的可乐一样，但问题是我们不知道岩浆混合后溶解的气体是如何表现的。这个项目将利用这一领域最新的分析进展。这些新技术将应用于关键火山喷发的样本，以了解溶解气体与不同岩浆混合时如何反应，以及这些过程在喷发前发生的时间尺度。时机至关重要，因为如果监测火山的科学家能够探测到岩浆混合过程（例如地震），那么我们就可以根据这项研究的数据预测将发生哪种类型的喷发。除此之外，我们还将使用高压和高温实验来重现我们的例子中喷涌和爆炸性喷发之前的条件。这个项目将改变我们对什么条件会导致更多的爆炸性喷发的理解。将这项研究的信息与监测数据相结合，将有助于限制爆炸性喷发造成的生命损失和经济损失。

10% of the world's population live within 100 km of a volcano. With the world's increasing population and stress on natural resources, volcanoes threaten more lives every day. Explosive volcanic eruptions can have devastating societal impacts on nearby populations, covering entire countries in ash, ruining crops and livestock, and cause a huge loss of human life. These eruptions can also have global effects, with the potential to impact air traffic, air quality and surface temperature. Conversely, lava flow or dome-forming (effusive) eruptions are generally less hazardous, with impacts more localised in the area immediately surrounding the volcano. The problem is that any one volcano can erupt both explosively and effusively with rapid changes in eruptive style. We currently do not understand what controls volcano eruptive style. This gap in our knowledge makes the impacts from an impending volcanic eruption very difficult to predict. For instance, with the small, but extremely disruptive explosive eruption of Eyjafjallajokull (Iceland) in 2010, while volcanologists could forecast that an eruption would occur within a few weeks, they were unable to forecast whether the impending eruption would be explosive or effusive. The ability to forecast what type of eruption will occur and how big an eruption will be would help to limit the loss of human life and reduce economic impacts by informing mitigation procedures such as evacuations. Unfortunately this goal cannot be achieved until we can determine what controls an eruption's 'explosive potential'. Most studies believe that shallow processes (<3 km) within the conduit (the magma feeder pipe) govern this transition, however recent work has suggested that deep processes (4-10 km) occurring whilst the magma is in storage (inside the magma chamber) may be key. A particularly important process is when two magmas with different temperatures and chemistries mix at depth, which occurs commonly before eruptions. The gas dissolved in a magma has a big part to play in this process, much like opening a bottle of coke once it has been shaken, but the problem is that we do not know how dissolved gasses behave as a result of magma mixing. This project will take advantage of recent analytical advances in this field. These new techniques will be applied to samples from key eruptions to understand how the dissolved gases reacted when mixed with different magmas and on what timescales these processes occurred before the eruption. The timing is critical, because if magma mixing processes can be detected by scientists monitoring a volcano (with earthquakes for example) then we may be able to forecast what type of eruption will occur based on the data from this study. Alongside this, we will also use high pressure and temperature experiments to recreate the conditions that occur before both our example effusive and explosive eruptions. This project will transform our understanding of what conditions promote more explosive eruptions. Combining the information from this study with monitoring data will help to limit the loss of life and economic damage that explosive eruptions cause.