Melt viscosity tracks the volcanic and magmatic evolution of the 2021 Tajogaite eruption, La Palma (Canary Islands)

Melt viscosity tracks the volcanic and magmatic evolution of the 2021 Tajogaite eruption, La Palma (Canary Islands)

After more than 50 years of repose, on September 19th, 2021, a volcanic eruption began at the Cumbre Vieja ridge on La Palma, Canary Islands. The combined effusive and explosive activity generated a > 12 km2 lava flow field with a new cone nearly 200 m higher than pre-eruptive topography and a vast tephra blanket. The immediate impact was locally devastating, destroying nearly 2000 buildings, blocking two main and numerous secondary roads, and inundating high-value agricultural land. The hybrid nature of the eruption and the observed variations in eruption intensity motivated a thorough investigation of bulk liquid viscosity at high temporal resolution. Collection of 82 lava samples was achieved at a near daily resolution over the course of the 85-day-long event (through the end of the eruption on December 13th, 2021). All the samples were remelted, and liquid viscosity was measured in a concentric cylinder viscometer from 1490 °C down to incipient crystallization temperatures. These data constitute the highest temporal resolution viscosity dataset obtained for an eruptive sequence to date. A tripartite viscosity pattern is identified at isothermal conditions: 1) during the fissure opening and establishing stage (days 1–20) a linear decrease in melt viscosity occurred; 2) during most of the eruption duration (days 21–70) viscosity was constant and 3) from day 70 until the end of the eruption viscosity increased again. We interpret this pattern as magma being extracted from different parts of the plumbing system over the course of the eruption. Accordingly, we show that viscosity time series can help shed light on some of the complexities of volcanic plumbing system. Additionally, the presented results highlight the monitoring potential of the viscosity assessment approach, specifically in regard to forecasting eruption behavior using direct information about magma mobility and detecting changes in magmatic plumbing system dynamics.

在沉寂了50多年之后，2021年9月19日，加那利群岛拉帕尔马岛的 Cumbre Vieja山脊开始火山喷发。喷溢和爆发活动共同形成了一个面积超过12平方千米的熔岩流场，一个比喷发前地形高出近200米的新火山锥以及一大片火山灰覆盖层。其直接影响在当地是毁灭性的，摧毁了近2000座建筑物，堵塞了两条主要公路和众多次要公路，淹没了高价值的农田。 此次喷发的混合性质以及观测到的喷发强度变化促使人们以高时间分辨率对总体液体粘度进行深入研究。在为期85天的事件过程中（直至2021年12月13日喷发结束），以近乎每日一次的频率采集了82个熔岩样本。所有样本都被重新熔化，并在同心圆柱粘度计中从1490°C到初始结晶温度测量了液体粘度。这些数据构成了迄今为止针对一个喷发序列所获得的最高时间分辨率的粘度数据集。 在等温条件下确定了一种三分式粘度模式：1）在裂缝开启和形成阶段（第1 - 20天），熔体粘度呈线性下降；2）在喷发的大部分时间（第21 - 70天），粘度保持恒定；3）从第70天直到喷发结束，粘度再次上升。我们将这种模式解释为在喷发过程中岩浆从管道系统的不同部分被抽取出来。因此，我们表明粘度时间序列有助于揭示火山管道系统的一些复杂性。此外，所呈现的结果凸显了粘度评估方法在监测方面的潜力，特别是在利用有关岩浆流动性的直接信息预测喷发行为以及检测岩浆管道系统动态变化方面。