dMODELS. A free software package to model volcanic deformation

Shallow magma accumulation in the crust often results in slight movements of the ground surface that can be measured using standard land-surveying techniques or satellite geodesy. Volcano geodesy uses measurements of crustal deformation to investigate volcano unrest and to search for magma reservoirs beneath active volcanic areas. A key assumption behind geodetic monitoring is that ground deformation of the Earth’s surface reflects tectonic and volcanic processes at depth (e.g., fault slip and/or mass transport) transmitted to the surface through the mechanical properties of the crust. Measurements and modeling of ground deformation are an indispensable component for any volcano monitoring strategy. The critical questions that emerge when monitoring volcanoes are how to (a) constrain the source of unrest, (b) improve the assessment of hazards associated with the unrest and (c) refine our ability to forecast volcanic activity. A number of analytical and numerical mathematical models are available in the literature that can be used to fit ground deformation to infer source location, geometry, depth and volume change. Analytical models offer a closed-form description of the volcanic source. This allows us, in principle, to readily infer the relative importance of any of the source parameters. The careful use of analytical models, together with high quality data sets can provide valuable insights into the nature of the deformation source (e.g., Battaglia and Hill, 2009). The simplifications that make analytical models tractable, however, may result in misleading interpretations. Sources are approximated by pressurized cavities in homogenous, elastic half-spaces filled with fluids. Although actual magmatic sources are certainly more complex, this approach can mimic the stress or potential field of the magma or other fluid sources beneath a volcano. The use of numerical models (e.g., finite element models) allows for evaluation of more realistic source characteristics and crustal properties (e.g., vertical and lateral mechanical discontinuities, complex source geometries, topography) but may require expensive proprietary software and powerful computers

Volcanic eruptions from ghost magma chambers

Recent studies have proposed that magma reservoirs crystallized to a virtually rigid crystal-mush can be partially remelted by diffusion of hot fluids. We show that for a crystal mush with the composition of a K-trachyte from the Campanian Ignimbrite (CI) Eruption, remelting can occur without a significant increase of the magma temperature, but simply by diffusion of H2O by the magmatic gases feeding the system. The CI origin is not the issue here, but rather the chemical and physical behavior of an almost solidified magma mass left over in a reservoir after a major eruption. To test our hypothesis, we run high pressure/high temperature laboratory experiments to study the kinetics of water diffusion, together with thermodynamics and fluid diffusion modelling. For small diffusivities, or large diffusion time, the remelting mechanism proposed above needs to be replaced by other processes as gas percolation or intrusion of a magmatic mass

Constraints on the active tectonics of the Friuli/NW Slovenia area from CGPS measurements and three-dimensional kinematic modeling

We use site velocities from continuous GPS (CGPS) observations and kinematic modeling to investigate the active tectonics of the Friuli/NW Slovenia area. Data from 42 CGPS stations around the Adriatic indicate an oblique collision, with southern Friuli moving NNW toward northern Friuli at the relative speed of 1.6 to 2.2 mm/a. We investigate the active tectonics using 3DMove, a three-dimensional kinematic model tool. The model consists of one indenter-shaped fault plane that approximates the Adriatic plate boundary. Using the ‘‘fault-parallel flow’’ deformation algorithm, we move the hanging wall along the fault plane in the direction indicated by the GPS velocities. The resulting strain field is used for structural interpretation. We identify a pattern of coincident strain maxima and high vorticity that correlates well with groups of hypocenters of major earthquakes (including their aftershocks) and indicates the orientation of secondary, active faults. The pattern reveals structures both parallel and perpendicular to the strike of the primary fault. In the eastern sector, which shows more complex tectonics, these two sets of faults probably form an interacting strike-slip system

Converting NAD83 GPS heights into NAVD88 elevations with LVGEOID, a hybrid geoid height model for the Long Valley volcanic region, California

A GPS survey of leveling benchmarks done in Long Valley Caldera in 1999 showed that the application of the National Geodetic Survey (NGS) geoid model GEOID99 to tie GPS heights to historical leveling measurements would significantly underestimate the caldera ground deformation (known from other geodetic measurements). The NGS geoid model was able to correctly reproduce the shape of the deformation, but required a local adjustment to give a realistic estimate of the magnitude of the uplift. In summer 2006, the U.S. Geological Survey conducted a new leveling survey along two major routes crossing the Long Valley region from north to south (Hwy 395) and from east to west (Hwy 203 – Benton Crossing). At the same time, 25 leveling bench marks were occupied with dual frequency GPS receivers to provide a measurement of the ellipsoid heights. Using the heights from these two surveys, we were able to compute a precise geoid height model (LVGEOID) for the Long Valley volcanic region. Our results show that although the LVGEOID and the latest NGS GEOID03 model practically coincide in areas outside the caldera, there is a difference of up to 0.2 m between the two models within the caldera. Accounting for this difference is critical when using the geoid height model to estimate the ground deformation due to magmatic or tectonic activity in the calder

Keeping watch over Colombia’s slumbering volcanoes

The Volcanological and Seismological Observatories of Manizales, Pasto and Popayan (Colombian Geological Survey) monitor and study the active volcanoes of Colombia using seismological, geodetic, geochemical and other techniques. Since 2009, permanent GNSS stations have been installed to complement classical geodetic measurements (e.g., tilt, EDM). At the moment, there are a total of 20 GNSS stations installed at Nevado del Ruiz, Cerro Machín, Puracé and Galeras volcanoes. Nevado del Ruiz has remained the most dynamic of the active Colombian volcanoes since its tragic eruption of 13 November 1985. The most significant deformation occurred between 2007 and 2012, when inflation, associated with magma migration and several small to moderate explosive eruptions in 2012 (VEI less or equal to 3), was observed. Galeras has experienced more than 25 moderate Vulcanian eruptions (VEI less or equal to 3) since 1989. In particular, the deformation network detected significant signals associated with magma migration and the extrusion of lava domes in 1991, 2005, 2008 and 2012. Puracé volcano has been the site of more than 10 minor eruptive episodes (VEI=2) in the past century, most recently in 1977. Monitoring of this volcano started in 1994. Unrest at Puracé since that time has been characterized by significant increases in seismic activity but with little or no deformation. We employ GAMIT/GLOBK to process GPS data from the monitoring network with support from the Volcano Disaster Assistance Program (U.S. Geological Survey). Additionally, differential processing is carried out using the commercial package Trimble 4D Control. Preliminary results for 2012 show no significant deformation at Puracé and Galeras volcanoes. On the other hand, the time series from Nevado del Ruiz shows a minor inflation (2-4 cm/yr) associated with the eruptive activity of 2012

Magma and fluid migration at Yellowstone Caldera in the last three decades inferred from InSAR, leveling and gravity measurements

We studied the Yellowstone caldera geological unrest between 1977 and 2010 by investigating temporal changes in differential Interferometric Synthetic Aperture Radar (InSAR), precise spirit leveling and gravity measurements. The analysis of the 1992–2010 displacement time series, retrieved by applying the SBAS InSAR technique, allowed the identification of three areas of deformation: (i) the Mallard Lake (ML) and Sour Creek (SC) resurgent domes, (ii) a region close to the Northern Caldera Rim (NCR), and (iii) the eastern Snake River Plain (SRP). While the eastern SRP shows a signal related to tectonic deformation, the other two regions are influenced by the caldera unrest. We removed the tectonic signal from the InSAR displacements, and we modeled the InSAR, leveling, and gravity measurements to retrieve the best fitting source parameters. Our findings confirmed the existence of different distinct sources, beneath the brittle-ductile transition zone, which have been intermittently active during the last three decades. Moreover, we interpreted our results in the light of existing seismic tomography studies. Concerning the SC dome, we highlighted the role of hydrothermal fluids as the driving force behind the 1977–1983 uplift; since 1983–1993 the deformation source transformed into a deeper one with a higher magmatic component. Furthermore, our results support the magmatic nature of the deformation source beneath ML dome for the overall investigated period. Finally, the uplift at NCR is interpreted as magma accumulation, while its subsidence could either be the result of fluids migration outside the caldera or the gravitational adjustment of the source from a spherical to a sill-like geometr

The 2008–2010 subsidence of Dallol Volcano on the spreading Erta Ale Ridge. InSAR observations and source models

In this work, we study the subsidence of Dallol, an explosive crater and hydrothermal area along the spreading Erta Ale ridge of Afar (Ethiopia). No volcanic products exist at the surface. However, a diking episode in 2004, accompanied by dike-induced faulting, indicates that Dallol is an active volcanic area. The 2004 diking episode was followed by quiescence until subsidence started in 2008. We use InSAR to measure the deformation, and inverse, thermoelastic and poroelastic modelling to understand the possible causes of the subsidence. Analysis of InSAR data from 2004–2010 shows that subsidence, centered at Dallol, initiated in October 2008, and continued at least until February 2010 at an approximately regular rate of up to 10 cm/year. The inversion of InSAR average velocities finds that the source causing the subsidence is shallow (depth between 0.5 and 1.5 km), located under Dallol and with a volume decrease between 0.63 and 0.26 106 km3/year. The most likely explanation for the subsidence of Dallol volcano is a combination of outgassing (depressurization), cooling and contraction of the roof of a shallow crustal magma chamber or of the hydrothermal system

A hypothetical therapeutic effect of light peripheral panretinal photocoagulation in neovascular age-related macular degeneration

Background: Vascular endothelial growth factor (VEGF) is a significant modulator of ocular angiogenesis, including that of neovascular age-related macular degeneration (nAMD). Intravitreal injection of anti-VEGF is the benchmark treatment for most retinal vascular diseases, including nAMD, diabetic maculopathy, and macular edema secondary to retinal venous occlusion. Anti-VEGF treatment is a high-frequency, time-consuming, non-cost-effective therapy, especially in countries and regions with limited resources. This treatment is easily restricted, and in practice, maintaining long-term periodic care is challenging for patients. Hypothesis: Light peripheral panretinal photocoagulation (PPRP) is applied in a mild form (barely visible mild light gray mark) anterior to the equator so as not to jeopardize the visual field. PPRP lessens the ischemia that causes neovascularization and decreases the metabolic demand in the peripheral retina. PPRP reduces serum angiopoietin-2 and VEGF levels in patients with type 2 diabetes mellitus with proliferative diabetic retinopathy. We propose using light PPRP to suppress VEGF secretion, aiming to attenuate the VEGF drive and halt choroidal neovascular growth in eyes with nAMD. Our regimen is based on two concepts: first, nAMD is a diffuse or generalized disease that affects the posterior segment; and second, PPRP is very effective in regressing diabetic retinopathy. PPRP has reportedly been successful in cases of macular edema (diabetic or following venous occlusion) resistant to VEGF antagonists. Light PPRP may be used as prophylaxis, adjunctive treatment, or monotherapy in nAMD when intravitreal injections of VEGF antagonists are not feasible. Conclusions: The established light PPRP therapy could be promising as a one-time, cost-effective therapy or prophylaxis in patients with nAMD or at high risk. This proposed modality could be suitable for patients who have injection phobia or prefer a one-time affordable therapy to the long-term monthly visits to retinologists. Future trials are necessary to verify the safety and efficacy of this proposed treatment modality in selected patients with nAMD

Fluorescein Leakage and Optical Coherence Tomography Features of Choroidal Neovascularization Secondary to Pathologic Myopia

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Heart Rate Control in Non-Paroxysmal Atrial Fibrillation. A New Indication for Ivabradine?

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