Caldera resurgence during the 2018 eruption of Sierra Negra volcano, Galápagos Islands.

Recent large basaltic eruptions began after only minor surface uplift and seismicity, and resulted in caldera subsidence. In contrast, some eruptions at Galápagos Island volcanoes are preceded by prolonged, large amplitude uplift and elevated seismicity. These systems also display long-term intra-caldera uplift, or resurgence. However, a scarcity of observations has obscured the mechanisms underpinning such behaviour. Here we combine a unique multiparametric dataset to show how the 2018 eruption of Sierra Negra contributed to caldera resurgence. Magma supply to a shallow reservoir drove 6.5 m of pre-eruptive uplift and seismicity over thirteen years, including an Mw5.4 earthquake that triggered the eruption. Although co-eruptive magma withdrawal resulted in 8.5 m of subsidence, net uplift of the inner-caldera on a trapdoor fault resulted in 1.5 m of permanent resurgence. These observations reveal the importance of intra-caldera faulting in affecting resurgence, and the mechanisms of eruption in the absence of well-developed rift systems

Optical wavelength tuning via actuation of a fluidic grating

Deformable optical elements may be physically altered through fluid displacement. We imprint a grating surface onto an elastomeric membrane by soft lithography. The membrane is installed as a flexible wall of a sealed fluidic chamber. Injection of excess fluid into the chamber induces expansion of the membrane, effectively varying the groove spacing of the imprinted grating. In transmission experiments using a broadband light source, we are able to achieve a 127.2-nm shift in peak wavelength with an injected fluid volume of 0.56 ml. A paraboloid model of the change in curvature of the grating during expansion accurately describes our experimental results

Fluidic actuation of an elastomeric grating

A fluidic chamber with an elastomeric grating membrane is fabricated. Grating groove spacing is modified through membrane deformation via fluid injection. Tunable diffraction output is demonstrated. At normal incidence, the diffraction angle changes by 14.2° and 9.8° for incident wavelengths 632.8 and 488 nm, respectively, with an injected fluid volume of 1 ml

State of stress and stress rotations: Quantifying the role of surface topography and subsurface density contrasts in magmatic rift zones (Eastern Rift, Africa)

In rift settings, the crustal stress field is dominated by extension, which leads to rift-parallel topography and basin alignments. However in some continental rift systems, some observables of the orientation of principal stresses show substantial deviations from these patterns. Such stress field rotations are currently poorly understood and could reflect the critical role of rift magmatism in the creation of topography, the plate state-of-stress, and volcanic and tectonic processes. Yet the role of magma intrusions, crustal thinning, and rift basin and flank topography on rift zone stress field rotations remain poorly quantified. The seismically- and volcanically-active Magadi-Natron-Manyara region of the East African Rift shows a 60 degrees local stress field rotation with respect to regional extension. Here, we test the hypothesis that such rotation is due to the cumulative effects of surface and subsurface loads (lateral subsurface density contrasts). We use analytical and calibrated numerical models of magmatic rift zones to simulate lithospheric deformation in the presence of magma bodies, crustal thinning, and topography to quantify their effect on intrusions and fault kinematics in a rift setting. Our 3D static models of a weakly extended rift suggest that surface topography influences shallow stress localization, whereas subsurface density contrasts play a larger role in lower crustal stress localization. Both patterns suggest a preferred region for melt storage beneath the rift valley. We show that the interaction between topography, crustal thinning, extension, and a pressurized magma reservoir could generate principal stress orientations consistent with the local stress rotation observed from earthquake focal mechanisms. Our results demonstrate how rift topography and the geometry of crustal thinning can guide magmatism and strain localization, highlighting the need for a three-dimensional treatment of rift kinematics

Outgassing through magmatic fractures enables effusive eruption of silicic magma

Several mechanisms have been proposed to allow highly viscous silicic magma to outgas efficiently enough to erupt effusively. There is increasing evidence that challenges the classic foam-collapse model in which gas escapes through permeable bubble networks, and instead suggests that magmatic fracturing and/or accompanying localized fragmentation and welding within the conduit play an important role in outgassing. The 2011–2012 eruption at Cordón Caulle volcano, Chile, provides direct observations of the role of magmatic fractures. This eruption exhibited a months-long hybrid phase, in which rhyolitic lava extrusion was accompanied by vigorous gas-and-tephra venting through fractures in the lava dome surface. Some of these fractures were preserved as tuffisites (tephra-filled veins) in erupted lava and bombs. We integrate constraints from petrologic analyses of erupted products and video analyses of gas-and-tephra venting to construct a model for magma ascent in a conduit. The one-dimensional, two-phase, steady-state model considers outgassing through deforming permeable bubble networks, magmatic fractures, and adjacent wall rock. Simulations for a range of plausible magma ascent conditions indicate that the eruption of low-porosity lava observed at Cordón Caulle volcano occurs because of significant gas flux through fracture networks in the upper conduit. This modeling emphasizes the important role that outgassing through magmatic fractures plays in sustaining effusive or hybrid eruptions of silicic magma and in facilitating explosive-effusive transitions