Measuring and modelling the crustal response to the 2011 eruption of Nabro volcano, Eritrea

Nabro volcano, situated to the east of the Afar Rift Zone, erupted on 12 June 2011. Eruptions at such off-rift volcanoes are infrequent, and consequently the plumbing systems are poorly understood. In this thesis I present post-eruption InSAR and seismic data to delineate the plumbing system of Nabro. I also investigate the temporal evolution of the system. I discuss my findings in reference to the tectonics of the Afar Rift Zone, off-rift volcanism and compare the findings to volcanoes world wide. I present 6 weeks of continuous seismic activity from an array of 7 seismic stations deployed following the eruption. For the analysis I locate and relocate hypocentres, determine focal mechanisms, calculate b-values and cross-correlate waveforms. I have relocated the hypocentres of 456 earthquakes and used the spatial pattern to interpret the local and regional crustal response to the eruption. The shallow earthquakes beneath Nabro's caldera delineate a NE-SW thrust fault which dips 45 degrees to the SE and extends across the caldera floor. This accommodates the stress change following the eruption, rather than movement on ring faults. The NE-SW fault plane is not associated with measurable surface deformation, indicating that it does not contribute much to the caldera deformation. A 10 km deep cluster highlights potential magma migration pathways directly beneath Nabro. On the flanks of the volcano, a linear pattern of earthquakes illuminate possible minor faults. There is also a cluster of earthquakes beneath Mallahle caldera at a depth of 6 km; the b-value for this cluster is 0.97 and is lower than that for clusters under Nabro (b=1.3). This implies that the earthquakes generated at Mallahle are not dominated by magmatic processes and occur in rock with a stronger rheology. Therefore, the seismicity I observed is likely due to changes in the stress field resulting from the subsidence at Nabro, and not caused by magma movement beneath Mallahle. TerraSAR-X and COSMO-SkyMed were both tasked to prioritise the acquisition of SAR data over the volcanic centre. During the following 15 months, Nabro was imaged 129 times by these satellites, with an acquisition every 5 days on average. I processed the 25 images acquired by TerraSAR-X between 1 July 2011 and 5 October 2012 on descending orbit 046, to create 34 interferograms. I complemented these with 19 images from ascending orbit 130 spanning 6 July 2011 to 10 October 2012 from ascending orbit 130, which I used to create 21 interferograms. I produced velocity ratemaps and time series using pi-RATE, showing subsidence of 25 cm/yr offset by 2 km to the SW of Nabro's caldera. COSMO-SkyMed satellite also imaged the volcano on a descending track between 26 June 2011 and 18 July 2012 within the Italian Space Agency project SAR4Volcanoes: a total of 64 images were acquired and used to produce 171 interferograms. I combined the InSAR data sets using a modelling approach to produce a detailed time series of the deflation of a Mogi source at 6.4 km depth. The time series shows that the volcano continued to subside for the entire period of observation, with the most rapid subsidence in the first 12 weeks, followed by subsidence at a slowly declining rate. I assessed the impact of atmosphere delays, using the outputs from ERA-Interim (ERA-I), a global atmospheric model computed by the European Centre for Medium-range Weather Forecasting (ECMWF), to correct each SAR acquisition. The atmospheric correction noticeably reduced the scatter in the time series, and removed the two atmospheric artefacts apparent in the COSMO-SkyMed time series. This result highlighted the importance of applying atmospheric corrections using independent sources of information. This contrasts with a standard approach of filtering in space and time which did not completely remove these atmospheric errors. Without the ERA-I correction the time series appeared to show pulses of recharge; with the correction continued subsidence is observed. I explore mechanisms that might explain the long-lived subsidence at Nabro volcano. In particular, I tested models of thermal contraction, degassing, fluid migration and viscoelasticity. Degassing is the most likely cause of deformation, although contraction due to cooling may also contribute. The long term post-eruption subsidence is unusual in comparison to other active volcanoes. I suggest that the low magma supply rate, combined with the high rate of passive degassing, induces an overall subsidence of the ground surface above Nabro

Earthquake relocations and InSAR analysis following the June 12th 2011 eruption of Nabro volcano, Afar

Nabro volcano sits on the southern part of Danakil block to the east of the Afar depression, on the Arabian plate. On the 12th June 2011, Nabro volcano suddenly erupted after being inactive for 10,000 years. The eruption caused a 17-km-long lava flow, a 15-km-high ash cloud, and ranks as one of the largest emissions of SO2 since the Mt. Pinatubo (1991) event. This eruption creates an important opportunity to use seismicity and surface deformation measurements to understand the subsurface magmatic system and deformation of a hazardous, off axis caldera during continental rupture. We installed a network of 8 seismometers around Nabro caldera which began recording on the 31st August and tasked SAR acquisitions from TerraSAR-X (TSX) and Cosmo-SkyMed (CSK) satellites. The SAR images used for this study post date the eruption. We used TSX stripmap mode images from ascending and descending orbits. Using a small baseline approach, we used 25 images acquired between the 1st July 2011 to the 5th October 2012 on descending orbit 046, to create 34 interferograms. We complemented these with 19 images from ascending orbit 130 spanning the 6th July 2011 to the 10th October 2012 from ascending orbit 130, which we used to create 21 interferograms. We produced a velocity ratemap and timeseries using π-RATE showing subsidence of up to 25cm/yr centred on Nabro. We used a Monte-Carlo hybrid downhill simplex technique to invert the dataset and found the best fitting solution as a mogi source at 6.9 ±1.1 km depth, and located at a 13.35 (lat) and 41.69 (long). The time dependence observed is consistent with a viscoelastic relaxation around the magma chamber, following depletion. Concurrent with the TSX acquisitions, CSK imaged the volcano on a descending track between 26th June 2011 and 18th July 2012 within the ASI project SAR4Volcanoes, and 64 images were used to produce 171 interferograms which were inverted to form a timeseries using a SBAS approach. This dataset has an overall subsidence signal, but the time series shows a shorter wavelength fluctuation of ground deformation, which is not apparent in the TSX data. We processed the seismic signals detected by the temporary local network and by a seismic station within a permanent regional array, to provide hypocentre locations for the period September-October, 2011. We used Hypoinverse-2000 to provide preliminary locations for events, which were then relocated using HypoDD. Absolute error after Hypoinverse-2000 processing was approximately ±2 and ±4 km in the horizontal and the vertical directions, respectively. Using HypoDD, relative errors were reduced to ±20 and ±30 m in the horizontal and vertical directions, respectively. The hypocentres show clusters of activity as well as aseismic regions. The majority of the earthquakes are located at the active vent, with fewer events located on the flanks. There is a smaller cluster of events to the south-west of Nabro beneath neighbouring Mallahle volcanic caldera, despite no eruption occurring here nor any post-eruptive deformation. This may imply some stress triggering mechanism or some pressure connection between the magma system of the two calderas. We present both the seismic and InSAR datasets as a joint approach to understand this eruption, as well as further implications for other ‘quiet calderas’

First recorded eruption of Nabro volcano, Eritrea, 2011

We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, Eritrea, which began on 12 June 2011. While no monitoring of the volcano was in effect at the time, it has been possible to reconstruct the nature and evolution of the eruption through analysis of re- gional seismological and infrasound data and satellite remote sensing data, supplemented by petrological analysis of erupted products and brief field surveys. The event is notable for the comparative rarity of recorded historical eruptions in the region and of caldera systems in general, for the prodi- gious quantity of SO2 emitted into the atmosphere and the significant human impacts that ensued notwithstanding the low population density of the Afar region. It is also relevant in understanding the broader magmatic and tectonic signifi- cance of the volcanic massif of which Nabro forms a part and which strikes obliquely to the principal rifting directions in the Red Sea and northern Afar. The whole-rock compositions of Editorial responsibility: G. Giordano the erupted lavas and tephra range from trachybasaltic to trachybasaltic andesite, and crystal-hosted melt inclusions contain up to 3,000 ppm of sulphur by weight. The eruption was preceded by significant seismicity, detected by regional networks of sensors and accompanied by sustained tremor. Substantial infrasound was recorded at distances of hundreds to thousands of kilometres from the vent, beginning at the onset of the eruption and continuing for weeks. Analysis of ground deformation suggests the eruption was fed by a shal- low, NW–SE-trending dike, which is consistent with field and satellite observations of vent distributions. Despite lack of prior planning and preparedness for volcanic events in the country, rapid coordination of the emergency response miti- gated the human costs of the eruption

Atmospheric CO2 sequestration in iron and steel slag: Consett, Co. Durham, UK

Carbonate formation in waste from the steel industry could constitute a non-trivial proportion of global requirements to remove carbon dioxide from the atmosphere at potentially low cost. To constrain this potential, we examined atmospheric carbon dioxide sequestration in a >20 million tonne legacy slag deposit in northern England, UK. Carbonates formed from the drainage water of the heap had stable carbon and oxygen isotope values between -12 and -25 ‰ and -5 and -18 ‰ for δ13C and δ18O respectively, suggesting atmospheric carbon dioxide sequestration in high pH solutions. From the analyses of solution saturation states, we estimate that between 280 and 2,900 tCO2 have precipitated from the drainage waters. However, by combining a thirty-seven-year dataset of the drainage water chemistry with geospatial analysis, we estimate that <1 % of the maximum carbon capture potential of the deposit may have been realised. This implies that uncontrolled deposition of slag is insufficient to maximise carbon sequestration, and there may be considerable quantities of unreacted legacy deposits available for atmospheric carbon sequestration

Effect of Hydrocortisone on Mortality and Organ Support in Patients With Severe COVID-19: The REMAP-CAP COVID-19 Corticosteroid Domain Randomized Clinical Trial.

Importance: Evidence regarding corticosteroid use for severe coronavirus disease 2019 (COVID-19) is limited. Objective: To determine whether hydrocortisone improves outcome for patients with severe COVID-19. Design, Setting, and Participants: An ongoing adaptive platform trial testing multiple interventions within multiple therapeutic domains, for example, antiviral agents, corticosteroids, or immunoglobulin. Between March 9 and June 17, 2020, 614 adult patients with suspected or confirmed COVID-19 were enrolled and randomized within at least 1 domain following admission to an intensive care unit (ICU) for respiratory or cardiovascular organ support at 121 sites in 8 countries. Of these, 403 were randomized to open-label interventions within the corticosteroid domain. The domain was halted after results from another trial were released. Follow-up ended August 12, 2020. Interventions: The corticosteroid domain randomized participants to a fixed 7-day course of intravenous hydrocortisone (50 mg or 100 mg every 6 hours) (n = 143), a shock-dependent course (50 mg every 6 hours when shock was clinically evident) (n = 152), or no hydrocortisone (n = 108). Main Outcomes and Measures: The primary end point was organ support-free days (days alive and free of ICU-based respiratory or cardiovascular support) within 21 days, where patients who died were assigned -1 day. The primary analysis was a bayesian cumulative logistic model that included all patients enrolled with severe COVID-19, adjusting for age, sex, site, region, time, assignment to interventions within other domains, and domain and intervention eligibility. Superiority was defined as the posterior probability of an odds ratio greater than 1 (threshold for trial conclusion of superiority >99%). Results: After excluding 19 participants who withdrew consent, there were 384 patients (mean age, 60 years; 29% female) randomized to the fixed-dose (n = 137), shock-dependent (n = 146), and no (n = 101) hydrocortisone groups; 379 (99%) completed the study and were included in the analysis. The mean age for the 3 groups ranged between 59.5 and 60.4 years; most patients were male (range, 70.6%-71.5%); mean body mass index ranged between 29.7 and 30.9; and patients receiving mechanical ventilation ranged between 50.0% and 63.5%. For the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively, the median organ support-free days were 0 (IQR, -1 to 15), 0 (IQR, -1 to 13), and 0 (-1 to 11) days (composed of 30%, 26%, and 33% mortality rates and 11.5, 9.5, and 6 median organ support-free days among survivors). The median adjusted odds ratio and bayesian probability of superiority were 1.43 (95% credible interval, 0.91-2.27) and 93% for fixed-dose hydrocortisone, respectively, and were 1.22 (95% credible interval, 0.76-1.94) and 80% for shock-dependent hydrocortisone compared with no hydrocortisone. Serious adverse events were reported in 4 (3%), 5 (3%), and 1 (1%) patients in the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively. Conclusions and Relevance: Among patients with severe COVID-19, treatment with a 7-day fixed-dose course of hydrocortisone or shock-dependent dosing of hydrocortisone, compared with no hydrocortisone, resulted in 93% and 80% probabilities of superiority with regard to the odds of improvement in organ support-free days within 21 days. However, the trial was stopped early and no treatment strategy met prespecified criteria for statistical superiority, precluding definitive conclusions. Trial Registration: ClinicalTrials.gov Identifier: NCT02735707

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

What causes subsidence following the 2011 eruption at Nabro (Eritrea)?

A major goal in volcanology is to be able to constrain the physical properties of a volcanic system using surface observations. The behaviour of a volcanic system following an eruption can provide powerful constraints on these properties and can provide valuable information for understanding future hazard. We use spatially and temporally dense observations of surface deformation following the 12 June 2011 eruption of Nabro (Eritrea) to place constraints on the mechanics of its subsurface volcanic system. Nabro was imaged 129 times by TerraSAR-X and COSMO-SkyMed satellites during a 15-month period following the eruption. We have produced a detailed time series of the line-of-sight (LOS) displacements at Nabro, finding that the volcano subsides during the entire observation period at a decaying rate. We found significant atmospheric artefacts remained in the data set after a standard spatio-temporal filter was applied. Applying an empirical correction using a linear phase-elevation relationship removed artefacts but also removed real topographically correlated deformation. Instead, we were able to correct each SAR acquisition using independent delay estimates derived from the ECMWF ERA-Interim (ERA-I) global atmospheric model. The corrected time series can be modelled with the deflation of a Mogi source at ∼ 6.4 ± 0.3 km depth. Modelling the time series using viscoelastic relaxation of a shell which surrounds a spherical magma chamber can explain the observed subsidence without a source of further volume loss if the magma is compressible. CO2 outgassing is also a possible cause of continued subsidence. Contraction due to cooling and crystallisation, however, is probably minor. If any post-eruptive recharge of the magmatic system at Nabro is occurring, the rate of recharge must be slower than the post-eruptive relaxation processes. Combined with the lack of pre-eruptive inflation, we suggest that recharge of the magmatic system at Nabro either occurs at a rate that is slower than our detection limit, or it occurs episodically. This case study demonstrates the power of long, dense geodetic time series at volcanoes

Atmospheric CO₂ Sequestration in Iron and Steel Slag: Consett, County Durham, United Kingdom

Carbonate formation in waste from the steel industry could constitute a nontrivial proportion of the global requirements for removing carbon dioxide from the atmosphere at a potentially low cost. To utilize this potential, we examined atmospheric carbon dioxide sequestration in a >20 million ton legacy slag deposit in northern England, United Kingdom. Carbonates formed from the drainage water of the heap had stable carbon and oxygen isotope values between −12 and −25 ‰ and −5 and −18 ‰ for δ¹³C and δ¹⁸O, respectively, suggesting atmospheric carbon dioxide sequestration in high-pH solutions. From the analyses of solution saturation states, we estimate that between 280 and 2900 tons of CO₂ have precipitated from the drainage waters. However, by combining a 37 year long data set of the drainage water chemistry with geospatial analysis, we estimate that <1% of the maximum carbon-capture potential of the deposit may have been realized. This implies that uncontrolled deposition of slag is insufficient to maximize carbon sequestration, and there may be considerable quantities of unreacted legacy deposits available for atmospheric carbon sequestration

High-resolution InSAR time series analysis following the 2011 eruption of Nabro Volcano, Eritrea: Implications for the mechanisms of post-eruptive subsidence

During continental rifting the majority of active volcanism typically becomes focused in a central rift axis. However, volcanic structures are also commonly found offset from the axis of spreading. Eruptions at such off-rift volcanoes are infrequent, and consequently the crustal processes are poorly understood. Nabro volcano, situated to the east of the Afar Rift Zone (ARZ), erupted on 12 June 2011. The eruption was only the second eruption of an off-rift volcano associated with the ARZ in modern times (since Dubbi volcano in 1861). We have recently published a study [Hamlyn et al., JGR 2014] comparing the post eruption ground displacement observed through TerraSAR-X InSAR with seismicity recorded at a local seismic array that we deployed following the eruption. This has provided new insights into the controls of caldera faults on subsidence. We now present a detailed analysis of the InSAR derived, time series of post-eruption subsidence using both TerraSAR-X and COSMO-SkyMed observations. We test competing hypotheses for the origin of the subsidence and stress the importance of atmospheric correction using independent data when interpreting topographically-correlated deformation at volcanoes. Following the June 2011 eruption at Nabro, TerraSAR-X and COSMO-SkyMed were both tasked to prioritize the acquisition of SAR data over the volcanic centre. During the following 15 months, Nabro was imaged 129 times by these satellites, with an acquisition every 5 days on average. Using a Small Baseline Subset (SBAS) approach, we processed the 25 images acquired by TerraSAR-X between 1 July 2011 and 5 October 2012 on descending orbit 046, to create 34 interferograms. We complemented these with 19 images from ascending orbit 130 spanning 6 July 2011 to 10 October 2012 from ascending orbit 130, which we used to create 21 interferograms. We produced velocity ratemaps and time series using π-RATE, showing subsidence of up to 25cm/yr centred on Nabro [Hamlyn et al., JGR 2014]. COSMO-SkyMed satellite also imaged the volcano on a descending track between 26 June 2011 and 18 July 2012 within the Italian Space Agency project SAR4Volcanoes: a total of 64 images were acquired and used to produce 171 interferograms. Each dataset were used to create a detailed time series of incremental deformation of the Nabro caldera using an SBAS approach. We combine these data sets using a modelling approach to produce a detailed time series of the deflation of a Mogi source at ~7 km depth. The raw and smoothed (temporal window of 70 days, spatial window of ~3km) time series show that the volcano continued to subside for the entire period, with a rapid subsidence in the first 12 weeks, followed by a slowly declining rate. In addition there are three apparent pauses in the subsidence. As the subsidence rate is approximately correlated with the topography of the volcano, we were concerned about the influence of atmospheric delays on our geophysical signal. To assess the impact of atmosphere delays, we use the outputs from ERA-Interim (ERA-I), a global atmospheric model computed by the European Centre for Medium-range Weather Forecasting (ECMWF), to correct each SAR acquisition. The atmospheric correction noticeably reduced the scatter in the time series, and removed the three apparent atmospheric artefacts. This result stresses the importance of applying atmospheric corrections using independent sources of information – the standard approach of filtering in space and time did not remove these atmospheric errors and without the ERA-I correction we would have produced a significantly different interpretation of the InSAR observations. Finally, we explore alternative mechanisms that might explain the long-lived subsidence at Nabro volcano. In particular, we test models of thermal contraction and cooling, visco-elastic relaxation, and degassing. The Nabro eruption was one of the largest volcanic emissions of SO2 since the 1991 eruption of Mt. Pinatubo. Therefore we compare the InSAR derived subsidence to the SO2 emissions observed by the IASI instrument. A correlation between the rate of SO2 emission and the rate of subsidence suggests a common underlying process, possibly magma cooling

Additional file 1 of What causes subsidence following the 2011 eruption at Nabro (Eritrea)?

The RMS difference in metres between the LOS displacement predicted by a Mogi source model for each epoch. Different satellites are shown with different colours. (JPG 204 kb