The thermal stealth flows of Santiaguito dome, Guatemala: Implications for the cooling and emplacement of dacitic block-lava flows
The thermal stealth flows of Santiaguito dome, Guatemala: Implications for the cooling and emplacement of dacitic block-lava flows
复制标题
危地马拉圣地亚哥圆顶的热隐形流：对英安岩块熔岩流冷却和就位的影响
DOI：
10.1130/0016-7606(2002)114
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发表时间：
2002
影响因子：
4.9
通讯作者：
W. Rose
中科院分区：
文献类型：
--
作者：
A. Harris;L. Flynn;O. Matías;W. Rose
厚的、缓慢移动的块状熔岩流与英质体系中的挤压活动有关，在流锋崩塌过程中，熔岩核的降压产生了devatating块状和火山灰流。2000年1月在危地马拉的Santiaguito收集了一个活跃的洋酸性块流的尺寸和罕见的热数据，提供了对冷却和就位机制的深入了解。尽管存在原始剪切带，但流速较低（12.5 m·d - 21）。流锋轴向部分比边缘区厚，且过陡。这种几何形状可以用轴向区较高的垂直速度梯度来解释，从而导致更频繁和更大体积的流前塌落。轴向带的崩塌也会渗透到更上层的流动中，但不足以使流动核心降压，从而产生块灰流。为了发生这样的块灰流，我们计算出速度和/或厚度的增加（由于坡度增加或地形限制）必须发生。虽然低表面温度使得阻挡流对短波红外传感器不可见，但低速度也有助于这些流动的隐身行为。然而，它们隐蔽的性质掩盖了这样一个事实，即它们可以延伸数公里，将块状和火山灰流源移动到更靠近脆弱社区的地方。
Thick, slow-moving block-lava flows are associated with extrusive activity in dacitic systems, where lava-core depressurization during flow-front collapse generates devas- tating block-and-ash flows. Dimensional and rare thermal data collected during Jan- uary 2000 for an active dacitic block flow at Santiaguito (Guatemala) provide insight into cooling and emplacement mechanisms. Flow velocity was low (12.5 m·d 21 ), in spite ginal shear zones. The axial part of the flow front was thicker than the marginal zones and was oversteepened. This geometry can be explained by a higher vertical velocity gradient in the axial zone, causing more frequent and larger-volume flow-front col- lapses. Axial-zone collapses also penetrate farther up flow, but not sufficiently to de- pressurize the flow core and generate a block-and-ash flow. For such a block-and- ash flow to occur, we calculate that an in- crease in velocity and/or thickness (due to increased slope or topographic confine- ment) must occur. Whereas low surface temperatures make block flows invisible to short-wave infrared sensors, the low veloc- ity also contributes to the stealthy behavior of these flows. Their stealthy nature, how- ever, masks the fact that they can extend many kilometers, moving block-and-ash flow sources closer to vulnerable communities.