Germán Padilla

Global CO2 emission from volcanic lakes

The global CO 2 discharge from subaerial volcanism has been estimated at ~300 Mt yr –1 . However, estimates of CO 2 emissions from volcanic lakes have not been considered. In order to improve this information, extensive research on CO 2 emissions of volcanic lakes worldwide has been performed. The observed normalized average CO 2 emission rates increase from alkaline (5.5 t km –2 d –1 ), to neutral (201.2 t km –2 d –1 ), to acid (614.2 t km –2 d –1 ) in volcanic lakes. Taking into account (1) normalized CO 2 emission rates, (2) the number of volcanic lakes in the world (~769), and (3) the fraction and average areas of the investigated alkaline, neutral, and acid volcanic lakes, the estimated global CO 2 emission from volcanic lakes is 117 ± 19 Mt yr –1 , with 94 ± 17 Mt yr –1 as deep-seated CO 2 . This study highlights the importance of a revision of the actual global CO 2 discharge from subaerial volcanism.

Diffusive helium emissions as a precursory sign of volcanic unrest

Significant increases in helium emissions from the soil and 3 He/ 4 He ratios in groundwater on El Hierro Island (Canary Islands, Spain) were observed prior to the 2011–2012 submarine eruption off the coast of the island. The changes of diffusive helium emissions rate were observed one month prior to the submarine eruption onset (12 October 2011) and the major increase preceded increases in seismic energy release during the volcanic unrest. Measured 3 He/ 4 He ratios in groundwaters from a well in El Hierro Island increased from 2–3 R A to 7.2 R A (R A = 3 He/ 4 He ratio in air) 1 month prior to the eruption onset, and reached a peak of 8.2 R A , indicating a dominant magmatic contribution to the dissolved gases in ground waters. 3 He/ 4 He values and diffusive helium emission studies have been extremely important for forecasting the onset of the volcanic unrest and subsequent volcanic eruption. An aseismic exsolution of magmatic gases from magma bodies beneath El Hierro Island through fractures and vertical permeability structures increased the diffusive helium emission rate prior to episodes of seismic energy release associated with the volcanic unrest.

An increasing trend of diffuse CO2 emission from Teide volcano (Tenerife, Canary Islands): geochemical evidence of magma degassing episodes

Multiple soil CO2 efflux surveys have been undertaken at the summit cone of Teide volcano, Tenerife, from 1997 to 2011, to determine the total CO2 emissions from the summit cone and to evaluate the temporal variations of CO2 efflux and their relationships with seismic–volcanic activity. Our results reveal significant fluctuations in degassing rate, which do not seem to be masked by atmospheric variations. These geochemical observations provide evidence for the unrest of the volcanic system, as has been suggested previously by anomalous seismic activity recorded in Tenerife during 22–29 April 2004. A new trend of increasing CO2 efflux and CO2/CH4 ratio in fumarolic gas discharges was observed from 2006 to 2009, suggesting that subsurface magma movement is the cause for the observed changes in the total output of diffuse CO2 emission at the summit cone of Teide.

Spatial and temporal variations of diffuse CO2 degassing at El Hierro volcanic system: Relation to the 2011–2012 submarine eruption

We report herein the results of extensive diffuse CO2 emission surveys performed on El Hierro Island in the period 1998–2012. More than 17,000 measurements of the diffuse CO2 efflux were carried out, most of them during the volcanic unrest period that started in July 2011. Two significant precursory signals based on geochemical and geodetical studies suggest that a magma intrusion processes might have started before 2011 in El Hierro Island. During the preeruptive and eruptive periods, the time series of the diffuse CO2 emission released by the whole island experienced two significant increases. The first started almost 2 weeks before the onset of the submarine eruption, reflecting a clear geochemical anomaly in CO2 emission, most likely due to increasing release of deep-seated magmatic gases to the surface. The second one, between 24 October and 27 November 2011, started before the most energetic seismic events of the volcanic-seismic unrest. The data presented here demonstrate that combined continuous monitoring studies and discrete surveys of diffuse CO2 emission provide important information to optimize the early warning system in volcano monitoring programs and to monitor the evolution of an ongoing volcanic eruption, even though it is a submarine eruption.

Carbon dioxide and helium dissolved gases in groundwater at central Tenerife Island, Canary Islands: chemical and isotopic characterization

Seismic-volcanic unrest was detected between 2004 and 2005 in the central and northwest zones of Tenerife Island (Canary Islands, Spain). With the aim of strengthening the program of geochemical and seismic-volcanic surveillance, a study of the origin, characteristics, and spatial distribution of dissolved carbon dioxide (CO2) and helium (He) gases in the volcanic aquifer of central Tenerife Island and around Teide volcano was carried out. This work also improves the hydrogeological and hydrogeochemical conceptual model of groundwater flow. Dissolved CO2 concentrations in sampled groundwater are several orders of magnitude higher than that of air-saturated water (ASW) suggesting a significant contribution of non-atmospheric CO2, mainly magmatic, confirmed through measurement of isotopic compositions (δ13CTDIC) and total dissolved inorganic carbon (TDIC) concentrations. A vertical stratification of dissolved CO2 and δ13CTDIC values was observed in the volcanic aquifer at the eastern region of Las Cañadas Caldera. Stratification seems to be controlled by both degree of magmatic CO2-water interaction and CO2 degassing and the original δ13Cco2(g) isotopic composition. The highest dissolved helium (4He) concentrations in groundwater seem to be related to radiogenic contributions resulting from water-rock interactions, and increase with residence time, instead of with endogenous magmatic inputs. Isotopic systematics show that the dissolved gases in groundwater of central Tenerife are variable mixtures of CO2–3He-rich fluids of volcanic-hydrothermal origin with both organic and atmospheric components. The results suggest that the eastern area of Las Cañadas Caldera, the South Volcanic Ridge, and the Teide summit cone are the areas most affected by degassing of the volcanic-hydrothermal system, and they are therefore the most suitable zones for future geochemical monitoring.

Geochemical evidence of different sources of long-period seismic events at Deception volcano, South Shetland Islands, Antarctica

Abstract This is the first detailed analysis of a CO2 diffuse degassing time series from Deception volcano, South Shetland Islands, Antarctica, performed during an episode of anomalously high long-period (LP) seismicity. Diffuse CO2 emissions measured by an automatic geochemical station between 7 December 2009 and 13 February 2010 showed an excellent temporal agreement with the LP seismicity in December 2009. The absence of such a temporal correlation with the second burst of seismicity that occurred in late January 2010 suggests a different source for this LP activity. This was confirmed by analysis of seismic array data. The LP seismicity observed during December 2009 was caused by fluid-driven cracks that originated from pressure fluctuations in the volcano-hydrothermal systems beneath Deception volcano that were probably caused by a deep injection of undegassed magma before December 2009. The diffuse CO2 degassing data have provided evidence of the activation of at least two different sources of seismicity during the study period at Deception volcano.

Diffuse Helium and Hydrogen Degassing to Reveal Hidden Geothermal Resources in Oceanic Volcanic Islands: The Canarian Archipelago Case Study

We report herein the results of soil gas geochemistry studies, focused mainly on nonreactive and/or highly mobile gases such as He and H2, in five mining licenses at Tenerife and Gran Canaria, Canary Islands, Spain, during 2011–2014. The primary objective was to sort the possible geothermal potential of these five mining licenses, thus reducing the uncertainty inherent to the selection of the areas with highest geothermal potential for future exploration works. By combining the overall information obtained by the statistical–graphical analysis of the soil He and H2 data, the spatial distribution of soil gas concentrations and the analysis of selected chemical ratios of the soil gas to evaluate the influence of deep-seating degassing, two of the five mining licenses (Garehagua and Abeque, both located in Tenerife Island) seemed to show the highest geothermal potential. These results will be useful for future implementation and development of geothermal energy in the Canaries, the only Spanish territory with potential high-enthalpy geothermal resources, thus the most promising area for high-enthalpy geothermal installations.