Intrusion and Eruption Dynamics on Active Galapagos Volcanoes

知识价值：该项目涉及加拉帕戈斯群岛两座不同的活火山的大地测量和地球物理监测，以了解岩浆的运输和储存，以及浅层侵入和喷发之间的平衡，所有这些都对火山危害评估具有重要意义。自2000年以来，对塞拉内格拉火山的GPS观测显示，在过去两年中，火山膨胀率急剧上升，2005年4月16日，岩浆室顶部沿活门断层发生非弹性破裂，并在秋季爆发。火山口底部的断裂作用可能对岩浆储存和火山口下岩浆储层的脱气历史产生深远的影响。有一种假说认为，活板门断层可以缓解与侵入和膨胀有关的弹性应力，从而使更大量的岩浆被储存在火山内部，而不是喷发出来。对火山气体排放和重力变化的连续测量，以及对现有GPS网络的更新，将为检验这一假设提供手段。该项目的第一阶段将通过维持2002年安装的L1和L1/L2 GPS网络，并进行后续的GPS运动，继续监测Sierra Negra的变形。全球定位系统的结果将与InSAR测量结果相结合，以便利用该技术的空间覆盖。同时测量火山喷出的气体将监测浅层岩浆储层中随体积变化的脱气过程。重力测量将对储层深处的体积和质量变化提供补充约束。本研究的结果将提供岩浆和大厦的物质性质、与室室填充率变化有关的地球化学和力学变化，以及大厦破坏导致侵入或喷发的原因和后果的约束。2005年5月13日，费尔南迪纳火山从位于西南火山口边缘的一个裂缝系统开始喷发。这种形式的喷发口，被称为环向裂缝，在加拉帕戈斯盾状火山中很常见，被认为是由火山内部的压力控制的，这些压力来自斜坡上的重力和岩浆室的膨胀。一种假说认为，在加拉帕戈斯盾状火山的下侧翼出现的周向裂缝和径向侵入是应变场相互作用的结果。有趣的是，1995年费尔南迪纳火山的上一次喷发是在西南侧翼的一个放射状喷发裂缝，就在2005年喷发地点的正下方。在费尔南迪纳安装的GPS活动网络是由美国国家科学基金会事先资助的，目的是捕捉像刚刚发生的这样的圆周事件，在火山喷发附近密集排列的地点。在费尔南迪纳，将实施喷发后GPS运动，以更好地了解应变场和裂缝形成机制。更广泛的影响：拟议的项目将为博士学位授予机构、本科学院和厄瓜多尔大学的学生和教师提供合作研究经验，并与查尔斯·达尔文研究站协调，继续为游客和当地居民提供教育项目的推广工作。

Intellectual Merit: This project concerns geodetic and geophysical monitoring of two distinct active volcanoes in the Galapagos Islands to understand magma transport and storage, and the balance between shallow intrusion and eruption, all of which have important implications for volcanic hazards assessment. GPS observations at Sierra Negra volcano since 2000 showed a dramatic increase in the rate of inflation over the past two years, culminating on April 16, 2005 with inelastic failure of the magma chamber roof along a trapdoor fault, and subsequent eruptions in the Fall. Faulting of the caldera floor may have a profound effect on magma storage and the degassing history of the subcaldera magma reservoir. One hypothesis is that trapdoor faulting relaxes elastic stress related to intrusion and inflation, allowing larger volumes of magma to be stored inside the volcano instead of erupting. Serial measurements of volcanic gas emissions and gravity changes, along with updates to existing GPS networks will provide means to test this hypothesis. The first phase of the project will continue monitoring of deformation at Sierra Negra by maintaining the continuous L1 and L1/L2 GPS network installed in 2002 and conducting a follow-up GPS campaign. The GPS results will be integrated with InSAR measurements in order to take advantage of the spatial coverage of that technique. Simultaneous measurement of volcanic gases emitted from fumaroles will monitor degassing processes in response to volume changes in the shallow magma reservoir. Gravity measurements will provide complementary constraints on volume and mass changes in the reservoir at depth. Results of this study will provide constraints on the material properties of the magma and edifice, geochemical and mechanical changes related to variable rates of chamber filling, and the causes and consequences of edifice failure leading to intrusion or eruption.Fernandina volcano began erupting on May 13, 2005 from a fissure system located on the southwestern caldera rim. This form of eruptive vent, termed a circumferential fissure, is common to Galapagos shield volcanoes and is thought to be governed by stresses acting within the volcano from both gravitational forces on the slopes and magma chamber inflation. One hypothesis is that circumferential fissures and radial intrusions, which occur on the lower flanks of Galapagos shield volcanoes, coexist as the result of strain field interaction. Interestingly, the previous eruption of Fernandina in 1995 was from a radial eruptive fissure on the southwest flank, immediately below the site of the 2005 eruption. The GPS campaign network installed at Fernandina with prior NSF funding was designed to capture a circumferential event like the one that has just occurred, with a dense array of sites in the vicinity of the eruption. At Fernandina, a post-eruption GPS campaign will be implemented to better understand the strain field and mechanisms of fissure formation. Broader Impacts: The proposed project will provide collaborative research experience for students and faculty from Ph.D.-granting institutions, undergraduate colleges, and Ecuadorian universities, and in coordination with the Charles Darwin Research Station to continue outreach efforts in educational programs for visitors and local residents.