Dyke apertures record stress accumulation during sustained volcanism.

The feedback between dyke and sill intrusions and the evolution of stresses within volcanic systems is poorly understood, despite its importance for magma transport and volcano instability. Long-lived ocean island volcanoes are crosscut by thousands of dykes, which must be accommodated through a combination of flank slip and visco-elastic deformation. Flank slip is dominant in some volcanoes (e.g., Kilauea), but how intrusions are accommodated in other volcanic systems remains unknown. Here we apply digital mapping techniques to collect > 400,000 orientation and aperture measurements from 519 sheet intrusions within Volcán Taburiente (La Palma, Canary Islands, Spain) and investigate their emplacement and accommodation. We show that vertically ascending dykes were deflected to propagate laterally as they approached the surface of the volcano, forming a radial dyke swarm, and propose a visco-elastic model for their accommodation. Our model reproduces the measured dyke-aperture distribution and predicts that stress accumulates within densely intruded regions of the volcano, blocking subsequent dykes and causing eruptive activity to migrate. These results have significant implications for the organisation of magma transport within volcanic edifices, and the evolution and stability of long-lived volcanic systems.

High resolution monitoring of strain fields in concrete during hydraulic fracturing processes.

We present a distributed fiber optic sensing scheme to image 3D strain fields inside concrete blocks during laboratory-scale hydraulic fracturing. Strain fields were measured by optical fibers embedded during casting of the concrete blocks. The axial strain profile along the optical fiber was interrogated by the in-fiber Rayleigh backscattering with 1-cm spatial resolution using optical frequency domain reflectometry (OFDR). The 3D strain fields inside the cubes under various driving pressures and pumping schedules were measured and used to characterize the location, shape, and growth rate of the hydraulic fractures. The fiber optic sensor detection method presented in this paper provides scientists and engineers an unique laboratory tool to understand the hydraulic fracturing processes via internal, 3D strain measurements with the potential to ascertain mechanisms related to crack growth and its associated damage of the surrounding material as well as poromechanically-coupled mechanisms driven by fluid diffusion from the crack into the permeable matrix of concrete specimens.