Rhyolite lava emplacement dynamics inferred from surface morphology
Rhyolite lava emplacement dynamics inferred from surface morphology
复制标题
DOI：
10.1016/j.jvolgeores.2020.106850
复制
发表时间：
2020-04-15
影响因子：
2.9
通讯作者：
Kenderes, Stuart M.
中科院分区：
文献类型：
--
作者：
Leggett, Tyler N.;Befus, Kenneth S.;Kenderes, Stuart M.
硅质熔岩的形态是在流动过程中流体动力条件作用下形成的。因此，仔细分析这些特征可以用来重建就位过程。我们使用无人航空系统和动态结构摄影测量技术收集了South Coulee和Obsidian Dome流纹岩熔岩（美国Mono-Inyo陨石坑）表面的厘米尺度空间分辨率图像。我们用来自美国西部的其他全新世流纹岩熔岩的现有图像补充了新获得的正形图和数字高程模型，包括Rock Mesa Dome（南姐妹，OR）， Newberry Flow（南姐妹，OR）， Obsidian Flow（纽本尼，OR）， Interlake Flow（纽伯里，OR）和Banco Bonito Flow（谷火山口，NM）。虽然存在许多形态特征，但我们的定量分析仅限于流动中常见的反复隆起和松散碎石块。脊间距和脊辐向表明，这些脊很可能是在侵位过程中受到挤压而形成的褶皱。压力脊间距在South Coulee为27 ~ 45 m，在Obsidian Dome为18 ~ 34 m。间隔通常随着离火山口越远越小。两种熔岩的脊振幅都在4到17之间，与离火山口的距离关系不大。流动内部脊顶的辐合点指向源口，为下伏熔岩底流产生的内生流动和褶皱的反向旋转提供了有力证据。靠近流动边缘的脊向流动锋靠近，表明外源流动在前进点变得越来越重要。在南古力和黑曜岩穹丘中，块体大小在通风口附近最大，向流锋方向逐渐减小。随着离排气口距离的增加，血凝块大小逐渐减小，这可能反映了导管积液率的降低。我们在流体动力学模型的解析解的透镜下解释我们的高分辨率现场测量，以估计就位时间尺度和相关速率。我们计算了相对较短的喷发时间尺度，范围从1个月到1个月
The morphology of a silicic lava is created by the fluid dynamic conditions that operated during flow. Careful analysis of these features can thus be used to reconstruct emplacement processes. We used unoccupied aerial system and structure-from-motion photogrammetry techniques to collect centimeter-scale spatial resolution imagery of the surfaces of South Coulee and Obsidian Dome rhyolite lavas (Mono-Inyo Craters, USA). We supplement the newly acquired orthomosaics and digital elevation models with existing imagery of other Holocene rhyolite lavas from across the western USA, including Rock Mesa Dome (South Sister, OR), Newberry Flow (South Sister, OR), Obsidian Flow (Newbeny, OR), Interlake Flow (Newberry, OR), and Banco Bonito Flow (Valles Caldera, NM). Although many morphologic features exist, we restrict our quantitative analyses to the recurrent ridges and blocks of loose rubble that are common to the flows. Ridge spacing and ridge vergence indicate the ridges are likely folds produced by compression during emplacement. Pressure ridge spacings range from 27 to 45 m at South Coulee and 18 to 34 m on Obsidian Dome. Spacing generally decreases with distance from the vent across both lavas. Ridge amplitudes range from 4 to 17 mat both lavas and show little correlation with distance from the vent. The vergence of the crest of the ridges in the flow interiors points back to the source vent, which provides strong evidence for endogenous flow and the backward rotation of folds produced by undertow of the underlying lava. Ridges near flow margins verge towards the flow front, demonstrating that exogenous flow becomes increasingly important at the point of advance. In both South Coulee and Obsidian Dome block sizes are largest near the vent, and gradually decrease towards the flow front. The gradual decrease in block size with increasing distance from the vent likely reflects decreasing effusion rates from the conduit. We interpret our high-resolution field measurements under the lens of analytical solutions to fluid dynamic models to estimate emplacement timescales and associated rates. We calculate relatively abbreviated eruptive timescales ranging from 1 month to