Nemesio M. Pérez

Diffuse emission of carbon dioxide, methane, and helium‐3 from Teide Volcano, Tenerife, Canary Islands

Diffuse emission of CO2, CH4 and ³He was investigated in the summit crater of Teide volcano, Tenerife, Canary Islands. The results indicate that Teide volcano releases abundant CO2 not only from its active crater, but also from its flanks as diffuse soil emanations. The spatial distribution of these emanations correlates quite closely with that of geothermal anomalies and manifestations. Our flux measurements indicate a total output of 380 ton·day−1 of CO2 and 1.6 on·day−1 of CH4 by diffuse degassing. From the ³He/CO2 ratios and the CO2 flux we estimate a diffuse ³He flux of 0.052 mol·year−1. Isotopic analysis of carbon in soil gas samples from sites of high soil CO2 flux indicates a magmatic origin for the CO2, also reported by high ³He/ 4He ratios of 5.50 and 5.87 Ra. The origin of methane is more uncertain with low δ13C values suggesting a biogenic contribution.

Reply to comment from Blanco et al. (2015) on “Evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of El Hierro (Canary Islands, Spain) by Pérez et al. [Bull. Volcanol. (2014), 76:882–896]

We begin by noting our appreciation for the comment from Blanco et al. (2015) on BEvidence from acoustic imaging for submarine volcanic activity in June 2012 off the west coast of El Hierro (Canary Islands, Spain)^ by Pérez et al. (2014) because it provides the opportunity to maintain an open scientific debate on this issue within the right framework. This is especially important because one of the co-authors of the comment from Blanco et al. (2015) had previously made a suggestion to us that we should not send the acoustic imaging data taken on June 28, 2012, for publication. In our opinion, this recommendation was detrimental to open scientific debate, which is always tremendously beneficial for the development of science. Secondly, the comment from Blanco et al. (2015) suggests that readers may have been confused; we emphasize that the submarine volcanic activity in 2012 off the west coast of El Hierro described by Pérez et al. (2014) was not, as inferred by Blanco et al. (2015), a volcanic eruption. It has been well documented (e.g., Italiano and Nuccio 1991; Caracausi et al. 2005; García et al. 2006; Pérez and Hernández 2007) that new and/or sporadic volcanic activities, such as relatively weak or significant visible degassing processes during volcanic unrest, have commonly occurred both in subaerial and submarine environments of volcanic systems. Such activity includes things that are not a volcanic eruption, which implies release of juvenile volcanic material and not just the sudden release of steam/gas. Pérez et al. (2014) used only acoustic imaging data taken on June 28 as evidence for submarine volcanic activity in 2012 off the west coast of El Hierro. Without this data, it would have been impossible for us to submit our scientific contribution for publication.

Diffuse emission of CO2 from Miyakejima volcano, Japan

Abstract Two soil gas surveys were carried out in May and September 1998 at Miyakejima volcano, in the Izu Mariana arc, Japan. CO 2 flux values for May and September surveys ranged from 0.1 to 18,150 g m −2 day −1 and from 0.1 to 9685 g m −2 day −1 , respectively. Statistical graphical analysis showed three overlapping populations. The spatial distribution of these emissions correlated quite closely with the geothermal and geological characteristics of the studied area. The structure releasing higher CO 2 is the summit cone Oyama and surrounding areas, where the most obvious geothermal features occur. A total output about 100–150 t day −1 is estimated from this area. A good correlation was observed between soil CO 2 flux and soil temperature at the summit caldera indicating extensive condensation of fumarolic steam within the upper part of Miyakejima. Carbon isotopic analysis of selected samples inside the summit caldera ( δ 13 C–CO 2 =−0.90‰ to −5.70‰) suggests a mixing of carbon derived from marine limestone and magmatic CO 2 while a clear biogenic origin ( δ 13 C–CO 2 =−14.76‰ to −25.52‰) is observed for the diffuse degassing of CO 2 outside summit caldera.

Diffuse emission of carbon dioxide from Cerro Negro Volcano, Nicaragua, Central America

We report the first detailed soil CO2 efflux survey carried out at Cerro Negro volcano, Nicaragua, Central America. Soil CO2 efflux values ranged from 0.5 to 35,000 g m−2 d−1. Spatial distribution of CO2 efflux shows that volcanic gas is mainly released from the summit crater and the fissures opened during the August 1999 eruption. The total CO2 output of Cerro Negro is conservatively estimated to be 2,800 t d−1, based on a study area of 0.58 Km². Contour maps of soil CO2 efflux, ground temperature, and δ13C(CO2) distributions support an important magmatic contribution for the total output of CO2 at Cerro Negro volcano.

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.

Precursory diffuse carbon dioxide degassing signature related to a 5.1 magnitude earthquake in El Salvador, Central America

Abstract Anomalous changes in the diffuse emission of carbon dioxide have been observed before some of the aftershocks of the 13 February 2001 El Salvador earthquake (magnitude 6.6). A significant increase in soil CO 2 efflux was detected 8 days before a 5.1 magnitude earthquake on 8 May 2001 25 km away from the observation site. In addition, pre- and co-seismic CO 2 efflux variations have also been observed related to the onset of a seismic swarm beneath San Vicente volcano on May 2001. Strain changes and/or fluid pressure fluctuations prior to earthquakes in the crust are hypothesized to be responsible for the observed variations in gas efflux at the surface environment of San Vicente volcano.

Helium-3 emission in and around Teide Volcano, Tenerife, Canary Islands, Spain

Air corrected ³He/4He ratios of fluid samples collected in and around Teide volcano, Tenerife, Canary Islands, ranged from 5.97 to 8.06 Ra. Helium-3 emission spatial distribution has a quite different pattern from other stratovolcanoes which show commonly a decreased trend for the ³He/4He ratio with respect to distance from the summit crater. This finding might be related to the volcano-tectonic setting differences between subduction-type and oceanic island-type statrovolcanoes. Radiogenic helium production is a significant process for the dilution of uprising derived-mantle fluids in and around subduction-type stratovolcanoes while it can be almost negligible for polygenetic volcanoes at oceanic islands.

Radon and helium in soil gases at Cañadas caldera, Tenerife, Canary Islands, Spain

Abstract The spatial distribution of soil radon was investigated at Canadas caldera, Tenerife, in two surveys carried out in the summers of 1992 and 1995 by using α-particle-sensitive cellulose nitrate films (Track-Etch) and emanometry, respectively. Soil helium was studied at several transects crossing different structural features of the area. Radon concentration measured by Track-Etch ranged from 1.0 to 1990 pCi/l while that measured by emanometry ranged from 0.1 to 618 pCi/l. Soil helium concentration varied from 5250 to 15 560 ppb with an average value of 6197 ppb. The spatial distribution of soil radon correlates quite closely with structural features (fractures, emission centers, etc.), where the main geothermal manifestations (fumaroles, steam ground and high subsurface temperature and gas contents) also occur. Areas showing high soil Rn concentrations occur at the summit of Teide, Roques de Garcia, caldera rim and south and east off side of the caldera. High soil helium anomalies correlate well spatially with those of radon, especially at the summit of Teide where relatively high 3 He/ 4 He isotopic ratios occur, suggesting a deep contribution for these emanations. Data indicate that radon and helium are supplied mostly from a deep source, with a minor contribution from U- and Th-rich shallow rocks and soils.

Thermal insights into the dynamics of Nyiragongo lava lake from ground and satellite measurements

This study was funded by Zanskar Producciones, Cabildo Insular de Tenerife, and the Instituto Volcanologico de Canarias. We are grateful to EUMETSAT for providing us SEVIRI data and to NASA for the Landsat 7 image. Letizia Spampinato thanks Dr S. Giammanco for funding her research activity on the VIGOR project.