EAGER: The Brittle and Extensional Origins of Structures on Silicic Lavas

了解熔岩流动的持续时间和速度对于评估与火山喷发相关的风险至关重要，特别是对于建立在火山侧翼的社区而言。对基拉韦厄火山(夏威夷)等持续喷发的火山进行了多年的观察，对流质的、快速流动的玄武岩熔岩流动有了复杂的理解；然而，对其他类型的熔岩缺乏类似程度的理解。高粘性、缓慢流动的硅质熔岩喷发在地质记录中很常见，但在人类时间尺度上很少见，因此人们对其了解很少。我们对硅质熔岩流动的大部分了解来自于对古代熔岩的研究，以及使用类似的粘性材料，如玉米糖浆的模拟。类似的模型和类似的地质物质，如冰(冰川)和泥浆(泥石流)预测，硅质熔岩将从火山喷口流出，因此，拉伸和延伸。这应该是一个主要的脆性过程，类似于在冰川上形成裂缝。然而，对古代熔岩的研究报告称，通过熔岩上表面的韧性褶皱，硅质熔岩被压缩和增厚。变形的方式对限制熔岩的内部温度和气体含量很重要，因为脆性破裂可能会释放出超压的气体和熔岩，在熔岩前进的整个过程中导致爆炸性喷发。相反，如果熔岩真的折叠，那么它们的流动速度必须比预期快得多，并将迅速向火山侧翼推进，危及下坡社区。这一结果将适用于未来加州东部、俄勒冈州、黄石国家公园和世界其他地方的硅质熔岩喷发。几名研究生将获得这一奖项的支持，他们将在现场和建模技术方面获得重要经验。在几个硅质熔岩的观察和文献回顾挑战了现有对硅质熔岩流在韧性流动过程中折叠的解释。美国西部喀斯喀特火山链的梅迪辛湖和纽贝里火山的硅质熔岩将是研究的重点。将绘制熔岩的地图，以了解其上表面的结构演变，注意与挤压有关的褶皱和其他结构的存在或不存在。如果如预期的那样，构造本质上主要是伸展的，例如裂缝和裂缝，那么与褶皱和挤压相关的模型将被修正。一个小型无人驾驶航空系统(Suas)将被用来生成高分辨率的上部表面可到达部分的地图，并生成可以在虚拟现实中进一步测量的建筑物的三维模型。褶皱和裂缝等结构以及岩石类型将在新的SUAS基础上绘制地图，并确定变形的类型、方向和大小。将使用激光雷达和卫星图像绘制熔岩的整个上表面，以检查结构和变形在更大区域的分布，并填补更详细的绘制之间的空白。这些数据结合在一起，将产生一个全面的结构模型，描述硅质熔岩从喷口到边缘的演变，并整合从模拟模型和基本理论对古代熔岩的理解。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Understanding the duration and speed of lava flows is central to assessing the risks associated with volcanic eruptions, especially for communities built on the flanks of volcanoes. Years of observations at persistently erupting volcanoes like Kilauea (Hawaii) have produced a sophisticated understanding of fluidal, fast-moving basaltic lava flows; however, a similar level of understanding is absent for other types of lava. Eruptions of highly viscous, slow-flowing silicic lavas are common in the geological record but are infrequent at human timescales, and therefore poorly understood. Most of our understanding of silicic lava flow comes from studies of ancient lavas coupled with simulations using analogous, viscous materials like corn syrup. Analog models and analogous geological materials like ice (glaciers) and mud (mudflows) predict that silicic lavas will flow away from the volcanic vent and therefore, stretch and extend. This should be a primarily brittle process akin to the formation of crevasses on glaciers. However, studies of ancient lavas report compression and thickening of silicic lavas through ductile folding of the lava's upper surface. The style of deformation is important in constraining the internal temperature and gas content of the lava as brittle fracturing will potentially release over-pressured gas and lava, causing explosive eruptions throughout the duration of the lava's advance. Conversely, if lavas do indeed fold then they must flow much faster than anticipated and will advance down the volcano's flanks rapidly, endangering downslope communities. The results will be applicable to future eruptions of silicic lavas in eastern California, Oregon, at Yellowstone National Park, and elsewhere around the world. Several graduate students will be supported with this award, and will gain important experience in both field and modeling techniques.Observations at several silicic lavas and review of literature challenge the existing interpretation of silicic lava flows being folded during ductile flow. Silicic lavas at Medicine Lake and Newberry volcanoes in the Cascade volcanic chain of the western United States will be focus of the study. Lavas will be mapped to understand the structural evolution of their upper surfaces, paying attention to the presence or absence of folds and other structures associated with compression. If, as expected, structures are dominantly extensional in nature, for example fractures and crevasses, models associated with folding and compression will be revised. A small unmanned aerial system (sUAS) will be used to generate high-resolution maps of accessible parts of the upper surfaces and to generate three-dimensional models of the structures that can measured further in virtual reality. Structures such as folds and crevasses, and rock types will be mapped on the new sUAS base to and establish the types, orientations and magnitudes of deformation. The entire upper surfaces of the lavas will be mapped using LiDAR and satellite imagery to examine the distribution of the structures and deformation over larger areas, and to fill-in gaps between more detailed mapping. Together these data will produce a comprehensive structural model that describes the evolving flow of silicic lava from the vent to the margins, and integrates understanding of ancient lavas from analog models and fundamental theory.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.