Extensive perched aquifer and structural implications revealed by 3D resistivity mapping in a Galapagos volcano
Extensive perched aquifer and structural implications revealed by 3D resistivity mapping in a Galapagos volcano
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DOI：
10.1016/j.epsl.2008.03.011
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发表时间：
2008-05-30
影响因子：
5.3
通讯作者：
Merlen, Godfrey
中科院分区：
文献类型：
--
作者：
d'Ozouville, Noemi;Auken, Esben;Merlen, Godfrey
由于火山岛地质构造的复杂性和地下数据的有限性，不同岛屿和同一岛屿的水文地质概念模型可能不同。加拉帕戈斯群岛与大多数有人居住的火山岛一样，面临着严重的水资源问题，这可能对其独特的原始生态系统产生重大影响，已被列入“濒危世界遗产名录”（2007年6月）。由于缺乏地质和水文数据，再加上难以获得实地测量数据，因此对岛屿水文地质的了解不足，对传统地球物理数据的解释也不令人信服。在这里，我们提出了三维（3-D）的电阻率地图，所谓的“无水”的圣克鲁斯岛，通过使用SkyTEM设备，机载瞬变电磁法。后者是非侵入性的，对难以进入的地形进行测量至关重要。我们表明，即使在高地形极端地下电阻率对比[1-6 000欧姆-米]，该方法是敏感的水文地质利益[50-200欧姆-米]的低电阻率层的深度约300米。地下电阻率结构的独特空间分辨率和三维视图允许识别两个水文地质重要区域：在南部山侧有一个以前未知的广泛的高位含水层（50 km（2）），以及在基底含水层中盐水楔的几何形状，其位置精确到几米，这一发现支持玄武岩岛屿上存在隐藏的高位含水层，到目前为止只能从水文地质研究中推断出来。它被认为是受到断层作用的影响。除了对独特但受到严重威胁的加拉帕戈斯群岛的水资源和生态系统管理的重要影响外，必须重新考虑火山岛的一些概念性流动模型。这种结构的存在下，在火山建筑物被认为是低强度层可能有助于解释潜在的灾难性滑坡的起源。(C)2008 Elsevier B. V.保留所有权利。
Due to the complexity of geological formations and limited subsurface data in volcanic islands, hydrogeological conceptual models can differ from one island to another and for the same island. The Galapagos Islands, like most inhabited volcanic islands, face important water resource problems which might have a major impact on their unique and pristine ecosystems, Endanger World Heritage list (June 2007). The scarcity of geological and hydrological data combined with the difficulty of access for field measurements lead to a Poor understanding of the island hydrogeology and unconvincing interpretation of traditional geophysical data. Here we present three dimensional (3-D) resistivity maps for the supposedly "waterless" Santa Cruz Island, obtained by using the SkyTEM device, a helicopter-borne transient electromagnetic method. The latter is non-invasive and measurements over inaccessible terrain were of vital importance. We show that even in high-relief terrain with extreme subsurface resistivity contrasts [1-6 000 ohm-m], the method is sensitive to low-resistivity layers of hydrogeological interest [50-200 ohm-m] to a depth of approximately 300 m. The unique spatial resolution and 3-D view of the subsurface resistivity structures allow identification of two zones of hydrogeological importance: a previously unknown extensive perched aquifer (50 km(2)) on the southern mountain side and the geometry of the salt-water wedge in the basal aquifer located with an accuracy of a few meters, This finding supports the existence of hidden perched aquifers on basaltic islands, until now only inferred from hydrogeological studies. It is seen to be affected by faulting. Beyond the vital implications for water resource and ecosystem management in the unique yet severely threatened Galapagos Islands, some conceptual flow models of volcanic islands have to be reconsidered. The presence of such structures in a volcanic edifice recognized as low strength layer may help to explain the origin of potentially catastrophic landslides. (C) 2008 Elsevier B.V. All rights reserved.