Investigating long-period and ultra-long-period oscillations in magma density of the current Cumbre Vieja eruption on La Palma (Canary Islands, Spain)

加那利群岛的火山喷发是罕见的事件。它们平均每几十年到几百年发生一次。在9月中旬，20 - 21日，拉帕尔马火山爆发，该岛上的火山活动中断了50年。现在已经很清楚，这次喷发是拉帕尔马群岛几千年来最大的一次喷发，也可能是该群岛几千年来最大的一次喷发。喷发开始时是一次裂隙喷发，注入岩浆形成几股熔岩流。在10月底的喷发风格发生了巨大的变化，随着巨大的熔岩喷泉的出现，火山爆发的爆发性越来越强，熔岩喷泉的高度超过了600米。这种活动的变化需要岩浆密度的急剧变化，因为岩浆从深处上升到表面喷发。我们怀疑密度降低了2到3倍。然而，目前在拉帕尔马没有仪器可以揭示这些密度变化。该项目旨在通过安装一个由三个重力仪组成的网络来量化岩浆密度的变化，这三个重力仪是对深度密度变化敏感的地球物理仪器。这些重力仪将战略性地安装在岩浆库的顶部，我们现在知道这些岩浆库连接在35公里到5公里深的地方，为目前的喷发提供能量。根据项目合作伙伴的初步调查结果，火山喷发的管道系统在几何上很复杂，需要大量的岩浆从大约10公里深的中级岩浆储存库横向流动到大约5公里深的最浅储存库。现在有机会以前所未有的细节研究沿着岩浆路径的密度的剧烈变化。岩浆补充的理论模型表明，岩浆的物理性质，如密度，在数小时至数周的时间内会发生变化。拉帕尔马火山的爆发为我们提供了一个前所未有的独特机会来测试这些理论。我们将能够利用先进的数值模型和数据查询工具，不仅量化岩浆密度的变化，而且量化其在时间和空间上的演变。此外，我们可以将我们的发现与公开可用的视频片段捕获的喷发动态联系起来，以研究岩浆密度变化与喷发活动之间的关系。这将为我们提供新的见解，了解拉帕尔马目前喷发的管道系统内的过程，以及更广泛地了解群岛和其他火山海洋岛屿其他地方的类似喷发。最后，项目中还有评估重力网络在帮助火山爆发预测和灾害评估方面的效益的余地。

Volcanic eruptions in the Canary Islands are rare events. They occur on average every few couple of decades to centuries. In mid-September 20 21 and eruption started on La Palma after a 50 year hiatus in eruptive activity on the island. It has now become clear that this eruption is the largest eruption on La Palma in several thousands of years and probably among the largest eruptions in the archipelago in several thousands of years.The eruption started out as a fissure eruption feeding magma to form several lava flows. At the end of October the eruption style changed drastically turning increasingly explosive with the advent of giant lava fountains reaching heights in excess of 600 m above the event.This change in activity requires drastic changes in magma density as magma rises from depth to erupt at the surface. We suspect a reduction in density by a factor of 2 to 3. However, there is currently no instrumentation on La Palma which can shed light on these density changes. This project aims at quantifying magma density changes by installing a network of three gravimeters: geophysical instruments that are sensitive to density changes at depth. The gravimeters will be strategically installed atop of magma reservoirs that we now know are connected between 35 km and around 5 km depth to feed the current eruption. Based on preliminary findings from project partners, the plumbing system of the eruption is geometrically complex and requires substantial lateral flow of magma from an intermediate-level magma storage at around 10 km depth to the most shallow storage at around 5 km depth. There is now the opportunity to study the drastic variations in density along the path of magma in unprecedented detail. Theoretical models of magma replenishment indicate variations in physical properties of magma such as density over periods of hours to weeks. The eruption on La Palma provides us with hence an unprecedented and unique opportunity to test these theories. We will be able to quantify not only the variations in magma density but also its evolution in time and space using advanced numerical models and data interrogation tools. Furthermore we can link our findings with the dynamics of the eruption that is captured by publicly available video footage to study the relationship between magma density changes and eruptive activity. This will afford us with new insights into processes within the plumbing system of the current eruption in La Palma and also more broadly for similar eruptions elsewhere in the archipelago and other volcanic ocean islands. Ultimately, there is scope in project to evaluate the benefit of gravimetric networks to aid eruption forecasting and hazard assessment.