Dune bedforms produced by dilute pyroclastic density currents from the August 2006 eruption of Tungurahua volcano, Ecuador.
Dune bedforms produced by dilute pyroclastic density currents from the August 2006 eruption of Tungurahua volcano, Ecuador.
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DOI：
10.1007/s00445-013-0762-x
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发表时间：
2013
影响因子：
3.5
通讯作者：
Dingwell, Donald B.
中科院分区：
文献类型：
--
作者：
Douillet, Guilhem Amin;Pacheco, Daniel Alejandro;Kueppers, Ulrich;Letort, Jean;Tsang-Hin-Sun, Eve;Bustillos, Jorge;Hall, Minard;Ramon, Patricio;Dingwell, Donald B.
2006 年 8 月，在通古拉瓦火山（厄瓜多尔）活动加剧期间，产生了一系列火山碎屑密度流。密集的火山碎屑流局限于排水网络的山谷，而稀薄的火山碎屑密度流则在河间溢出，在那里沉积了由暴露在地表的交叉分层火山灰沙丘床形组成的孤立体。这里介绍了 300 多种沙丘地貌的描述、测量和分类。根据形状、内部结构和几何形状（长度、宽度、厚度、沙丘面角和背风面角以及沙丘面长度）确定了四种类型的沙丘床形。 (1)“细长沙丘地貌”具有光滑的形状，并且长度（在流动方向上）大于宽度或厚度。内部分层由块状和粗粒物质构成的岩层结构、厚透镜体层组成，与细层层交替，这些层层连续沉积在岩层和背风面，形成随着波峰向上游迁移的渐进结构。 (2)“横向沙丘地貌”表现为垂直于水流方向的线性沙丘，长度和宽度相等。在内部，这些床型表现出细层状的积灰层床组，并伴有上游波峰迁移。床具的陡峭截断仅在斯托斯一侧可见。 (3)“月状沙丘地貌”呈棒形，层理形态与横向沙丘相似。最后，（4）“二维沙丘床形”宽度远大于长度，呈现线性波峰并组织成序列。细长的沙丘床型仅出现在近端沉积区。在远端灰体中发现了横向、月形和二维沙丘地貌。灰体内形成的沙丘地貌类型在空间上有所不同，横向沙丘地貌主要出现在沉积区的起始处，在中间区域过渡到月形沙丘地貌，而二维沙丘地貌仅出现在沉积物的侧向和远端边缘。后者也出现在水流向上流动的地方。细长的沙丘床形是由具有高容量和能力的基于颗粒和牵引流边界的流沉积而成的。它们可能是在亚临界环境中通过阻挡物料一侧的材料而形成的。我们不会将它们解释为反沙丘或“滑槽和水池”结构。横向沙丘床形的尺寸和交叉层状模式被解释为由具有显着沉积率的低能力电流造成的，但我们排除了它们作为“反沙丘”的解释。类似的结论也适用于月形沙丘床形，其弯曲形状是由取决于床形厚度的沉降速率造成的。最后，形成二维沙丘地貌，其中横向传输超过纵向传输；即，在低速区域中水流能够横向扩散的区域。我们认为，具有上游波峰迁移的加剧灰床组是在亚临界流动条件下形成的，其中牵引床荷运输不如同时悬浮的沉降物重要。这产生了差异悬垂性，无需进一步返工。我们建议将这一过程产生的结构命名为“回归攀登沙丘”。推测水流速度的快速下降可以解释它们的沉积，这可能是由影响整个母体水流的水力跳跃引发的。该过程原则上适用于任何类型的颗粒密度电流。本文的在线版本 (doi:10.1007/s00445-013-0762-x) 包含补充材料，可供授权用户使用。
A series of pyroclastic density currents were generated at Tungurahua volcano (Ecuador) during a period of heightened activity in August 2006. Dense pyroclastic flows were confined to valleys of the drainage network, while dilute pyroclastic density currents overflowed on interfluves where they deposited isolated bodies comprising dune bedforms of cross-stratified ash exposed on the surface. Here, the description, measurement, and classification of more than 300 dune bedforms are presented. Four types of dune bedforms are identified with respect to their shape, internal structure, and geometry (length, width, thickness, stoss and lee face angles, and stoss face length). (1) “Elongate dune bedforms” have smooth shapes and are longer (in the flow direction) than wide or thick. Internal stratification consists of stoss-constructional, thick lensoidal layers of massive and coarse-grained material, alternating with bedsets of fine laminae that deposit continuously on both stoss and lee sides forming aggrading structures with upstream migration of the crests. (2) “Transverse dune bedforms” show linear crests perpendicular to the flow direction, with equivalent lengths and widths. Internally, these bedforms exhibit finely stratified bedsets of aggrading ash laminae with upstream crest migration. Steep truncations of the bedsets are visible on the stoss side only. (3) “Lunate dune bedforms” display a barchanoidal shape and have stratification patterns similar to those of the transverse ones. Finally, (4) “two-dimensional dune bedforms” are much wider than long, exhibit linear crests and are organized into trains. Elongate dune bedforms are found exclusively in proximal deposition zones. Transverse, lunate, and two-dimensional dune bedforms are found in distal ash bodies. The type of dune bedform developed varies spatially within an ash body, transverse dune bedforms occurring primarily at the onset of deposition zones, transitioning to lunate dune bedforms in intermediate zones, and two-dimensional dune bedforms exclusively on the lateral and distal edges of the deposits. The latter are also found where flows moved upslope. Elongate dune bedforms were deposited from flows with both granular-based and tractional flow boundaries that possessed high capacity and competence. They may have formed in a subcritical context by the blocking of material on the stoss side. We do not interpret them as antidune or “chute-and-pool” structures. The dimensions and cross-stratification patterns of transverse dune bedforms are interpreted as resulting from low competence currents with a significant deposition rate, but we rule out their interpretation as “antidunes”. A similar conclusion holds for lunate dune bedforms, whose curved shape results from a sedimentation rate dependent on the thickness of the bedform. Finally, two-dimensional dune bedforms were formed where lateral transport exceeds longitudinal transport; i.e., in areas where currents were able to spread laterally in low velocity zones. We suggest that the aggrading ash bedsets with upstream crest migration were formed under subcritical flow conditions where the tractional bedload transport was less important than the simultaneous fallout from suspension. This produced differential draping with no further reworking. We propose the name “regressive climbing dunes” for structures produced by this process. A rapid decrease in current velocity, possibly triggered by hydraulic jumps affecting the entire parent flows, is inferred to explain their deposition. This process can in principle hold for any kind of particulate density current. The online version of this article (doi:10.1007/s00445-013-0762-x) contains supplementary material, which is available to authorized users.
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影响因子：
3.5
作者：
Douillet, Guilhem Amin;Tsang-Hin-Sun, Eve;Kueppers, Ulrich;Letort, Jean;Pacheco, Daniel Alejandro;Goldstein, Fabian;Von Aulock, Felix;Lavallee, Yan;Hanson, Jonathan Bruce;Bustillos, Jorge;Robin, Claude;Ramon, Patricio;Hall, Minard;Dingwell, Donald B.
通讯作者：
Dingwell, Donald B.
DOI：
10.1016/j.jvolgeores.2012.02.011
发表时间：
2012-05-01
影响因子：
2.9
作者：
Andrews, Benjamin J.;Manga, Michael
通讯作者：
Manga, Michael
DOI：
10.1016/s0377-0273(01)00196-2
发表时间：
2001-09-15
影响因子：
2.9
作者：
Cagnoli, B;Ulrych, TJ
通讯作者：
Ulrych, TJ
影响因子：
3.5
作者：
Colella, A;Hiscott, RN
通讯作者：
Hiscott, RN
影响因子：
12.1
作者：
ANDERSON, RS
通讯作者：
ANDERSON, RS