Eruptive and shallow conduit dynamics during Vulcanian explosions: insights from the Episode IV block field of the 1912 eruption of Novarupta, Alaska
Eruptive and shallow conduit dynamics during Vulcanian explosions: insights from the Episode IV block field of the 1912 eruption of Novarupta, Alaska
复制标题
瓦肯尼亚爆炸期间的喷发和浅层管道动力学：来自 1912 年阿拉斯加诺瓦鲁普塔喷发的第四集区块场的见解
作者：
S. J. Isgett;B. Houghton;S. Fagents;S. Biass;A. Burgisser;L. Arbaret
对1912年诺瓦鲁普塔火山喷发的火山阶段的~1300个幼年和岩屑块的研究为岩浆状态提供了新的见解，因为喷发从持续的普林尼期过渡到圆顶生长。在距离喷口约2-3公里半径范围内对主要是弹道喷出的块体进行了测量和取样，并提供了一幅在反复小爆炸中岩浆破碎之前动态和复杂的浅管道的图片。极端的管道不均匀性表现在各种各样的英安岩块类型中，包括浮岩质、致密、带状和非熔结角砾岩碎屑，所有这些都具有不同程度的表面面包壳。我们提出了新的块体岩性和大小的地图，使第四集最彻底映射火山存款的日期。富含特定岩性的扇形区域以及区块大小数据表明发生了多次小规模爆炸。块轨迹的建模，以再现现场数据表明，喷射速度范围从50到124米/秒，中位数为70米/秒。我们建议，个别爆炸起源于一个异质的浅管道，其特征在于由对比纹理和vesiculation状态的岩浆域的并列，并在短的垂直和水平的长度尺度在这些域之间的接触，不同的纹理的亲密的本地混合。在我们的模型中，每次爆炸都只破坏了管道的浅层，并在管道内挖掘了不同的局部口袋。这与现有的重复性火山爆发模型形成对比，并表明第四集的动力学比水平分层管道的简单渐进式自上而下疏散更为复杂。
The study of ~1300 juvenile and lithic blocks from a Vulcanian phase of the 1912 eruption of Novarupta provides new insight into the state of the magma as an eruption passes from sustained Plinian to dome growth. Blocks that were predominantly ballistically ejected were measured and sampled within an ~2–3-km radius from vent and supply a picture of a dynamic and complex shallow conduit prior to magma fragmentation in repeated small explosions. Extreme conduit heterogeneity is expressed in the diverse range of dacitic block types, including pumiceous, dense, banded, and variably welded breccia clasts, all with varied degrees of surface breadcrusting. We present new maps of block lithology and size, making Episode IV the most thoroughly mapped Vulcanian deposit to date. Sectorial regions rich in specific lithologies together with the block size data suggest multiple, small explosions. Modeling of block trajectories to reproduce the field data indicates that ejection velocities range from 50 to 124 m/s with a median of ~70 m/s. We propose that individual explosions originated from a heterogeneous shallow conduit characterized both by the juxtaposition of magma domains of contrasting texture and vesiculation state and by the intimate local mingling of different textures on short vertical and horizontal length scales at the contacts between these domains. In our model, each explosion disrupted the conduit to only shallow depths and tapped diverse, localized pockets within the conduit. This contrasts with existing models for repetitive Vulcanian explosions, and suggests that the dynamics of Episode IV were more complex than a simple progressive top-down evacuation of a horizontally stratified conduit.
快速和缓慢：不同的岩浆上升速率是火神爆发的机制
影响因子：
5.3
作者：
Cassidy M
通讯作者：
Cassidy M