The May 2005 eruption of Fernandina volcano, Galapagos: The first circumferential dike intrusion observed by GPS and InSAR
The May 2005 eruption of Fernandina volcano, Galapagos: The first circumferential dike intrusion observed by GPS and InSAR
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DOI：
10.1007/s00445-010-0433-0
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发表时间：
2011-08-01
影响因子：
3.5
通讯作者：
Ruiz, Andres
中科院分区：
文献类型：
--
作者：
Chadwick, William W., Jr.;Jonsson, Sigurjon;Ruiz, Andres
2005年5月，加拉帕戈斯群岛的费尔南迪纳火山沿着与火山口边缘平行的环形裂缝喷发，熔岩流沿着火山陡峭的西南斜坡流下，持续了数周。这是InSAR和GPS观测到的第一次周向岩脉侵入，从而提供了一个机会来确定这些神秘结构的地下几何形状，这些结构在加拉帕戈斯火山上很常见，但在其他地方很少见。2002年至2006年喷发前后的地面变形可以通过火山口下两个独立岩浆库的膨胀来模拟：一个深度约为1公里的浅喷泉和一个深度约为5公里的深点源，我们推断这一系统在2005年喷发时也存在。共喷发变形以2005年喷发裂缝附近的隆起为主，叠加在以火山口为中心的广泛沉降上。通过包括各种平面位错组合来模拟2005年的周向岩脉侵入，对共喷发变形进行了建模。我们发现单个平面堤不能同时匹配InSAR和GPS数据。我们最适合的模型包括三个沿铰链线连接的平面堤岸，以模拟一个弯曲的凹壳，该壳在表面向火山口急剧倾斜（类似于45-60度），在与水平火山口下基台连接的深度更平缓地倾斜（类似于12-14度）。深点震源在浅基岩之下。这个模拟的岩浆系统的几何形状与费尔南迪纳熔岩的岩石学是一致的，这表明环向喷发利用了系统的最浅部分，而径向喷发则来自更深的层次。费尔南迪纳火山最近的喷发历史也与这样一种观点相一致，即周向和径向侵入有时处于应力反馈关系，并且在时间上彼此交替。
The May 2005 eruption of Fernandina volcano, Galapagos, occurred along circumferential fissures parallel to the caldera rim and fed lava flows down the steep southwestern slope of the volcano for several weeks. This was the first circumferential dike intrusion ever observed by both InSAR and GPS measurements and thus provides an opportunity to determine the subsurface geometry of these enigmatic structures that are common on Galapagos volcanoes but are rare elsewhere. Pre- and post- eruption ground deformation between 2002 and 2006 can be modeled by the inflation of two separate magma reservoirs beneath the caldera: a shallow sill at similar to 1 km depth and a deeper point-source at similar to 5 km depth, and we infer that this system also existed at the time of the 2005 eruption. The co-eruption deformation is dominated by uplift near the 2005 eruptive fissures, superimposed on a broad subsidence centered on the caldera. Modeling of the co-eruption deformation was performed by including various combinations of planar dislocations to simulate the 2005 circumferential dike intrusion. We found that a single planar dike could not match both the InSAR and GPS data. Our best-fit model includes three planar dikes connected along hinge lines to simulate a curved concave shell that is steeply dipping (similar to 45-60A degrees) toward the caldera at the surface and more gently dipping (similar to 12-14A degrees) at depth where it connects to the horizontal sub-caldera sill. The shallow sill is underlain by the deep point source. The geometry of this modeled magmatic system is consistent with the petrology of Fernandina lavas, which suggest that circumferential eruptions tap the shallowest parts of the system, whereas radial eruptions are fed from deeper levels. The recent history of eruptions at Fernandina is also consistent with the idea that circumferential and radial intrusions are sometimes in a stress-feedback relationship and alternate in time with one another.