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

EAGER：硅质熔岩结构的脆性和伸展起源

• 批准号: 1935764
• 负责人: Graham Andrews
• 金额: $ 3.54万
• 依托单位: West Virginia University Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-08-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1935764&HistoricalAwards=false
• 关键词: EAGER; Brittle; Extensional; Origins; Structures

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.

了解熔岩流的持续时间和速度是评估火山爆发风险的核心，尤其是对火山两侧的社区。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，使人们对流动的、快速移动的玄武岩熔岩流有了更深入的了解；然而，对其他类型的熔岩却没有类似的认识。高粘性、缓慢流动的硅质熔岩的喷发在地质记录中很常见，但在人类的时间尺度上并不常见，因此人们对其知之甚少。我们对硅熔岩流的大部分理解来自对古代熔岩的研究，以及使用类似的粘性物质（如玉米糖浆）进行模拟。类似的模型和类似的地质物质，如冰（冰川）和泥（泥石流）预测，硅熔岩将从火山口流出，因此，拉伸和延伸。这应该是一个主要的脆性过程，类似于冰川裂缝的形成。然而，对古代熔岩的研究报告了通过熔岩上表面的韧性折叠而产生的硅熔岩的压缩和增厚。这种变形方式对限制熔岩内部温度和气体含量很重要，因为脆性压裂可能会释放出压力过大的气体和熔岩，在熔岩前进的整个过程中引发爆炸性喷发。相反，如果熔岩确实折叠，那么它们的流动速度肯定比预期的要快得多，并将迅速向火山侧翼推进，危及下坡的社区。研究结果将适用于未来在加州东部、俄勒冈州、黄石国家公园和世界其他地方爆发的硅熔岩。几名研究生将获得该奖项的支持，并将获得在现场和建模技术方面的重要经验。对几个硅质熔岩的观测和文献综述对现有的硅质熔岩流在韧性流动中被折叠的解释提出了挑战。美国西部喀斯喀特火山链的梅迪辛湖和纽贝里火山的硅熔岩将是研究的重点。将绘制熔岩地图，以了解其上表面的结构演变，注意是否存在褶皱和其他与压缩相关的结构。如果像预期的那样，构造在本质上主要是伸展的，例如裂缝和裂缝，那么与褶皱和压缩相关的模型将被修改。小型无人机系统（sUAS）将用于生成上层表面可访问部分的高分辨率地图，并生成可以在虚拟现实中进一步测量的结构三维模型。将在新的sUAS基础上绘制褶皱、裂缝等构造和岩石类型，并确定变形类型、方向和大小。将利用激光雷达和卫星图像绘制熔岩的整个上表面，以检查更大范围内结构和变形的分布，并填补更详细地图之间的空白。这些数据将产生一个综合的结构模型，该模型描述了从火山口到边缘的硅熔岩的演化流动，并整合了模拟模型和基础理论对古代熔岩的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

The fold illusion: The origins and implications of ogives on silicic lavas

褶皱错觉：硅质熔岩上尖顶的起源和影响

• DOI: 10.1016/j.epsl.2020.116643
• 发表时间: 2020
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Andrews, Graham D.M.;Kenderes, Stuart M.;Whittington, Alan G.;Isom, Shelby L.;Brown, Sarah R.;Pettus, Holly D.;Cole, Brenna G.;Gokey, Kailee J.
• 通讯作者: Gokey, Kailee J.