Feasibility of Monitoring the Hontomín (Burgos, Spain) CO2 Storage Site Using a Deep EM Source

Geophysical methods have been used experimentally during the last decade, a period of strong development, being adopted as complementary techniques for characterizing and monitoring hydrocarbon and gas reservoirs. In this study, we evaluated the ability of the controlled source electromagnetic (CSEM) method to monitor the storage of CO₂ at the Research Laboratory on Geological Storage of CO₂ at Hontomín (Burgos, Spain). Two aspects of the CSEM monitoring were examined considering the geoelectrical structure at the site, the technological constraints and the noise conditions of the Hontomín area. Borehole-to-surface simulations were performed to evaluate the detectability of the resistivity changes in the reservoir and the capacity to determine the location of the CO₂ plume. The synthetic time-lapse study explores the possibilities of CSEM monitoring with a deep electric source. Three depths of the source are analyzed: above the plume, inside the plume, and beneath the stored CO₂. In terms of the Hontomín storage site, the study confirmed that a deep electric source located beneath the injection depth can provide valuable information on the behavior of the stored CO_2.     

ESR/U-series chronology of the Neanderthal occupation layers at Galería de las Estatuas (Sierra de Atapuerca,Spain)

The Galería de las Estatuas is a Mousterian site located within the Cueva Mayor-Cueva del Silo karstic system at the Sierra de Atapuerca (Burgos, Spain). This site is characterised by an important Upper Pleistocene stratigraphic sequence in which a large number of lithic artefacts exhibiting clear Mousterian affinities and a rich assemblage of faunal remains have been found.Additionally, this site has yielded a foot phalanx of a clear Neanderthal affinities and its sediment has yielded Neanderthal mitochondrial and nuclear DNA.Two test pits, GE-I and GE-II, have been excavated since 2008 which have been divided in 5 and 2 lithostratigraphical units, respectively. A minimum age of 45 ka cal BP for this site was obtained by radiocarbon dating in GE-II. This chronology was refined using single-grain Optically Stimulated Luminescence (OSL: 80–112 ka in GE-I and 70–79 ka in GE-II) and single-grain thermally transferred OSL (TT-OSL). Although in all case TT-OSL ages were systematically older than their single-grain counterparts. The detrital sequence is sealed by a flowstone whose base is dated to 53.7 ± 3.5 ka cal BP using U-series dating.In order to better constrain the age of this site, nine herbivorous teeth were collected from the whole sedimentary sequence to be dated by the ESR/U-series dating method though only seven provided modelled ages. Six of them were collected from levels 2 to 5 of the GE-I test pit while the last tooth was taken from level 2 of the GE-II test pit. Our results, ranging between 80 and 110 ka, are in agreement with those obtained by single grain TT-OSL and suggest that the sedimentological levels containing Mousterian lithic artefacts and faunal and human remains began to be deposited during the second part of the MIS5. These results fill a temporal gap in the chronology of the Atapuerca sites for which no contemporary MIS5 date was obtained until recently.     

Monitoring of Guadalentín valley (southern Spain) through a fast SAR Interferometry method

Ground subsidence is a critical problem in populated areas, which requires attention and routine monitoring. Specifically, subsidence related to the exploitation of aquifer systems is of particular interest in terms of risk for the possible damage to buildings and availability of water resources. We propose to realise a survey of the aquifer systems near the city of Lorca, southern Spain, using Synthetic Aperture Radar Interferometry (InSAR) with a light method necessitating a small number of interferograms rather than analysing hundreds of radar images. We computed nine interferograms with good coherence over the years 2004 and 2005. We analysed them by a two-step filtering process in order to characterise the atmospheric contribution and the ground deformation. We are then able to identify two deforming areas and quantify subsidence rates at 0.20 ± 0.02 mm/day south of Lorca and southeast to the city of Alhama de Murcia with the same efficiency as the studies using sophisticated InSAR methods. Using continuous records of water levels in boreholes, we deduced a mean storage coefficient (S_k) at 4.1 × 10^− 3 which is very close to the previous published values, and coincides in this case to an inelastic deformation mode of all the system. With this value, we determine the groundwater level variations from the measurements of the ground subsidence.     

Bioavailability of heavy metals in water and sediments from a typical Mediterranean Bay (Málaga Bay,Region of Andalucía,Southern Spain)

Concentrations of heavy metals were measured in sediment and water from Málaga Bay (South Spain). In the later twentieth century, cities such as Málaga, have suffered the impact of mass summer tourism. The ancient industrial activities, and the actual urbanization and coastal development, recreation and tourism, wastewaters treatment facilities, have been sources of marine pollution. In sediments, Ni was the most disturbing metal because Ni concentrations exceeded the effects range low (ERL), concentration at which toxicity could start to be observed in 85% of the samples analyzed. The metal bioavailability decreased in the order: Cd > Ni > Pb > Cu > Cr. In the sea water samples, Cd and Pb were the most disturbing metals because they exceeded the continuous criteria concentration (CCC) of US EPA in a 22.5% and 10.0% of the samples, respectively. Statistical analyses (ANOVA, PCA, CA) were performed.     

Chronological reconstruction of metal contamination in the Port of Maó (Minorca, Spain)

In this work we discuss the historical record of metals as derived from a sediment core from the Port of Maó (Minorca, Spain), the second natural largest harbour in Europe. The sedimentation rate derived from radionuclide profiles increased by a factor of five since the 1960s due to the urbanisation of the town waterfront. Metal concentrations showed two different trends: (i) Pb and Sn inputs started during the second half of the 19th century and remained relatively high until mid-20th century; and (ii) Ag, Cd, Ni, Zn, Cu and Cr accumulation began in the 1940s, peaking in the late 1970s. The commissioning of a submarine outfall in 1978 reduced metal concentrations in subsequently deposited sediments since, thereafter, urban and industrial wastes have been dumped out of the estuary. This study also shows that evaluating the quality of sediments on the basis of surface concentrations may be misleading.     

Modeling the Mogi magma source centre of the Santorini (Thera) volcano, Aegean Sea, Greece, 1994–1999, based on a numerical-topological approach

The aim of this study is the refinement of the dynamics of a recent (1994?C1999) minor, slow-inflation episode of the Santorini (Thera) volcano, famous for the Minoan (??3600 B.C.) eruption and the identification of the parameters of the magmatic source responsible for the inflation. Based on the Mogi source equations, on geodetic observations of base-line changes, on a topological, grid-search approach and on the reasonable assumption that the magma source remained practically stable in map view during the inflation period, we have been able to refine the location and depth (approximately 2.7 km) of the magma center. A tendency for increase of the magma pressure with time, roughly corresponding to a sphere with radius between 30 and 60 m, and a short deflation interval were also documented. The overall modeling was based on a topological method of inversion in two steps and for a selected 4-D grid. At a first step the system of Mogi-source equations was approximated by the intersection of the 4-D subspaces (defined by sets of grid points) each satisfying one observation equation on the basis of a grid-search procedure. At a second step, the best estimate of the Mogi source solution and its full variance-covariance matrix were defined using a common stochastic approach. The overall approach leads to a solution of a system of equations focusing on a 4-D space bounding significant minima in the misfits between model and observed values, and not on solutions focusing on single points, usually trapped in local minima. This study is important to understand a new phase of volcanic unrest since January 2011, while the proposed methodology, inspired from traditional navigation methods may be useful for other inversion problems leading to redundant systems of highly non-linear equations with n unknowns (i.e. topological solutions in the n-D space).     

Holocene vertical deformation along the coastal sector of Mt. Etna volcano (eastern Sicily,Italy): Implications on the time–space constrains of the volcano lateral sliding

A detailed survey of morphological and biological markers of paleo-shorelines has been carried out along the coastal sector of Mt. Etna volcano (eastern Sicily, Italy), in order to better define causes and timing of vertical deformation. We have mapped markers of raised Holocene shorelines, which are represented by beach rocks, wave-cut platforms, balanid, vermetid and algal rims. The timing of coastal uplift has been determined by radiocarbon dating of shells collected from the raised paleo-shorelines and, to correctly assess the total amount of tectonic uplift of the coast during the Late Holocene, we have compared the elevation-age data of sampled shells to the local curve of Holocene sea-level rise. Taking into account the nominal elevation of the associated paleo-shorelines, an uplift rate of 2.5–3.0 mm/year has been estimated for the last 6–7 ka. This general process of uplifting is only locally interrupted by subsidence related to flank sliding of the volcanic edifice, measured at docks and other manmade structures, and by acceleration along the hinge of an active anticline and at the footwall of an active fault. Based on this new data we suggest more precise time–space constraints for the dynamics of the lower eastern flank of Mt. Etna volcano.     

Geochemical model of a magmatic–hydrothermal system at the Lastarria volcano, northern Chile

Lastarria volcano (25°10′ S, 68°31′ W; 5,697 m above sea level), located in the Central Andes Volcanic Zone (northern Chile), is characterized by four distinct fumarolic fields with outlet temperatures ranging between 80°C and 408°C as measured between May 2006–March 2008 and April–June 2009. Fumarolic gasses contain significant concentrations of high temperature gas compounds (i.e., SO₂, HCl, HF, H₂, and CO), and isotopic ratios (³He/⁴He, δ¹³C–CO₂, δ¹⁸O–H₂O, and δD–H₂O) diagnostic of magmatic gas sources. Gas equilibria systematics, in both the H₂O-H₂-CO₂-CO-CH₄ and alkane–alkene C₃ system, suggest that Lastarria fumarolic gasses emanate from a superheated vapor that is later cooled and condensed at relatively shallow depths. This two-stage process inhibits the formation of a continuous aquifer (e.g., horizontal liquid layer) at relatively shallow depth. Recent developments in the magmatic gas system may have enhanced the transfer and release of heat causing shallow aquifer vaporization. The consequent pressure increase and aquifer vaporization likely triggered the inflation events beginning in 2003 at the Lastarria volcano.     

The 1963–1964 eruption of Agung volcano (Bali, Indonesia)

The February 1963 to January 1964 eruption of Gunung Agung, Indonesia’s largest and most devastating eruption of the twentieth century, was a multi-phase explosive and effusive event that produced both basaltic andesite tephra and andesite lava. A rather unusual eruption sequence with an early lava flow followed by two explosive phases, and the presence of two related but distinctly different magma types, is best explained by successive magma injections and mixing in the conduit or high level magma chamber. The 7.5-km-long blocky-surfaced andesite lava flow of ～0.1?km³ volume was emplaced in the first 26?days of activity beginning on 19 February. On 17 March 1963, a major moderate intensity (～4?×?10⁷?kg?s^?1) explosive phase occurred with an ～3.5-h-long climax. This phase produced an eruption column estimated to have reached heights of 19 to 26?km above sea level and deposited a scoria lapilli to fine ash fall unit up to ～0.2?km³ (dense rock equivalent—DRE) in volume, with Plinian dispersal characteristics, and small but devastating scoria-and-ash flow deposits. On 16 May, a second intense 4-h-long explosive phase (2.3?×?10⁷?kg?s^?1) occurred that produced an ～20-km-high eruption column and deposited up to ～0.1?km³ (DRE) volume of similar ash fall and pyroclastic flow deposits, the latter of which were more widespread than in the March phase. The two magma types, porphyritic basaltic andesite and andesite, are found as distinct juvenile scoria populations. This indicates magma mixing prior to the onset of the 1963 eruption, and successive injections of the more mafic magma may have modulated the pulsatory style of the eruption sequence. Even though a total of only ～0.4?km³ (DRE volume) of lava, scoria and ash fall, and scoria-and-ash pyroclastic flow deposits were produced by the 1963 eruption, there was considerable local damage caused mainly by a combination of pyroclastic flows and lahars that formed from the flow deposits in the saturated drainages around Agung. Minor explosive activity and lahar generation by rainfall persisted into early 1964. The climactic events of 17 March and 16 May 1963 managed to inject ash and sulfur-rich gases into the tropical stratosphere.     

Remagnetization mechanism of Lower Cretaceous rocks from the Organyà Basin (Pyrenees,Spain)

Widespread Cretaceous remagnetization is documented in several Mesozoic basins in North Central Spain. Organyà Basin (South Central Pyrenean foreland) is atypical in the sense that the lower part of the rock sequence (Berriasian-Barremian limestones) is remagnetized while the upper portion (Aptian-Albian marls) is not (Dinarès-Turell and García-Senz, 2000). Here, this view is confirmed by the analysis of 41 new paleomagnetic sites over the entire basin, so that a 3D view is obtained. Thermoviscous resetting of the natural remanent magnetization can be ruled out, hence the remagnetization is chemical in origin. A positive breccia-test on remagnetized strata constrains the remagnetization age to older than the Paleocene-Eocene, when the backthrust system was active. The remagnetization is argued to have occurred early in the geological history of the Organyà Basin either in the elevated geothermal gradient regime during the syn-rift extension or at the earliest phase of the later compression. Burial is considered the most important cause combined with the lithological effect that limestones are more prone to express remagnetization than marls. The observed pressure solution in the remagnetized limestone is likely associated with the remagnetization, whereas it is unlikely that externally derived fluids have played an important role.     

Geoelectrical structure of the central zone of Piton de la Fournaise volcano (Réunion)

 A study of the geoelectrical structure of the central part of Piton de la Fournaise volcano (Réunion, Indian Ocean) was made using direct current electrical (DC) and transient electromagnetic soundings (TEM). Piton de la Fournaise is a highly active oceanic basaltic shield and has been active for more than half a million years. Joint interpretation of the DC and TEM data allows us to obtain reliable 1D models of the resistivity distribution. The depth of investigation is of the order of 1.5 km but varies with the resistivity pattern encountered at each sounding. Two-dimensional resistivity cross sections were constructed by interpolation between the soundings of the 1D interpreted models. Conductors with resistivities less than 100 ohm-m are present at depth beneath all of the soundings and are located high in the volcanic edifice at elevations between 2000 and 1200 m. The deepest conductor has a resistivity less than 20 ohm-m for soundings located inside the Enclos and less than 60–100 ohm-m for soundings outside the Enclos. From the resistivity distributions, two zones are distinguished: (a) the central zone of the Enclos; and (b) the outer zone beyond the Enclos. Beneath the highly active summit area, the conductor rises to within a few hundred meters of the surface. This bulge coincides with a 2000-mV self-potential anomaly. Low-resistivity zones are inferred to show the presence of a hydrothermal system where alteration by steam and hot water has lowered the resistivity of the rocks. Farther from the summit, but inside the Enclos, the depth to the conductive layers increases to approximately 1 km and is inferred to be a deepening of the hydrothermally altered zone. Outside of the Enclos, the nature of the deep, conductive layers is not established. The observed resistivities suggest the presence of hydrated minerals, which could be found in landslide breccias, in hydrothermally altered zones, or in thick pyroclastic layers. Such formations often create perched water tables. The known occurrence of large eastward-moving landslides in the evolution of Piton de la Fournaise strongly suggests that large volumes of breccias should exist in the interior of the volcano; however, extensive breccia deposits are not observed at the bottom of the deep valleys that incise the volcano to elevations lower than those determined for the top of the conductors. The presence of the center of Piton de la Fournaise beneath the Plaine des Sables area during earlier volcanic stages (ca. 0.5 to 0.150 Ma) may have resulted in broad hydrothermal alteration of this zone. However, this interpretation cannot account for the low resistivities in peripheral zones. It is not presently possible to discriminate between these general interpretations. In addition, the nature of the deep conductors may be different in each zone. Whatever the geologic nature of these conductive layers, their presence indicates a major change of lithology at depth, unexpected for a shield volcano such as Piton de la Fournaise. Received: 3 November 1999 / Accepted: 15 September 1999     

Combined electromagnetic, geochemical and thermal surveys of Taal volcano (Philippines) during the period 2005–2006

Since 1572, 33 phreatic to phreatomagmatic eruptions have occurred on Taal volcano (Philippines), some of them causing several hundred casualties. Considering the time delay between two consecutive eruptions, there is an 88% probability that Taal volcano should have already erupted. Since 1992, several phases of seismic activity have been recorded accompanied by ground deformation, opening of fissures, and surface activity. The volcanic activity of Taal appears to be controlled by dike injections and magma supply, buffered by a hydrothermal system that releases fluids and heat through boiling and subsequent steaming. In early 2005, a multidisciplinary project was launched for studying the hydrothermal activity. To map the hydrothermal system, combined surveys were carried out to investigate self-potential, total magnetic field, ground temperature and carbon dioxide soil degassing, along with satellite thermal imaging of the Main Crater Lake. The elevated temperatures and high concentrations of carbon dioxide, as well as electromagnetic anomalies, indicate large-scale hydrothermal degassing. This process is enhanced along the tectonic features (e.g., crater rim and faults) of the volcano, while active fissures opened along the E–W northern flank during the 1992–1994 seismic activity. Heat and fluids from the hydrothermal system are essentially released in the northern part of the crater, which is bounded to the South by a suspected NW–SE fault along which seismicity seems to take place, and dikes are thought to be intruded. During the January 2005 surveys, a new seismic crisis started, and the felt earthquakes prompted spontaneous evacuation of hundreds of inhabitants living on the volcano. Repeated surveys show changes of self-potential, total magnetic field, and ground temperature with time, without any noticeable spatial enlargement. These observations suggest that the northern flank located between the crater rim and the 1992–1994 fissures is connected with a deep thermal source in Main crater and is reactivated during seismic crises. This sector could be subjected to flank failure.     

Seismicity of Ruapehu volcano,New Zealand, 1971–1996: a review

From 1971 until 1995, the style of seismicity at Ruapehu changed little, reflecting a period of relatively low eruptive activity and consequent long-term stability within the vent system. Volcanic earthquakes and volcanic tremor were both dominated by a frequency of about 2 Hz. Volcanic earthquakes accompanied all phreatic and phreatomagmatic eruptions, but not small hydrothermal eruptions that originated within Crater Lake. Furthermore, more than half of the M_L>3 volcanic earthquakes and changes in the reduced displacement of 2 Hz volcanic tremor by as much as a factor of 20 occurred without any accompanying eruptive activity. Three and 7 Hz volcanic tremor were also recorded, although never at lower-elevation seismometers. At times, this tremor was stronger at the summit seismometer than the 2 Hz tremor. Their source regions were independent of the 2 Hz source, and located at shallower depths. Volcano-tectonic earthquakes were generally unrelated to eruptive activity. The seismicity accompanying the 1995–1996 eruptive activity was significantly different from that of the period 1971 to 1995, and included volcanic tremor with a frequency of less than 1 Hz, simultaneous changes in the amplitude of the previously independent 2 Hz and 7 Hz volcanic tremor, and finally a change in the frequency content of volcanic earthquakes and volcanic tremor from 2 Hz to wideband. Path transmission effects play an important role in determining the characteristics of seismograms at Ruapehu. The presence of Crater Lake affects both the style of eruptions and the accompanying seismicity.     

Petrology, magnetostratigraphy and geochronology of the Miocene volcaniclastic Tepoztlán Formation: implications for the initiation of the Transmexican Volcanic Belt (Central Mexico)

The volcaniclastic Tepoztlán Formation (TF) represents an important rock record to unravel the early evolution of the Transmexican Volcanic Belt (TMVB). Here, a depositional model together with a chronostratigraphy of this Formation is presented, based on detailed field observations together with new geochronological, paleomagnetic, and petrological data. The TF consists predominantly of deposits from pyroclastic density currents and extensive epiclastic products such as tuffaceous sandstones, conglomerates and breccias, originating from fluvial and mass flow processes, respectively. Within these sediments fall deposits and lavas are sparsely intercalated. The clastic material is almost exclusively of volcanic origin, ranging in composition from andesite to rhyolite. Thick gravity-driven deposits and large-scale alluvial fan environments document the buildup of steep volcanic edifices. K-Ar and Ar-Ar dates, in addition to eight magnetostratigraphic sections and lithological correlations served to construct a chronostratigraphy for the entire Tepoztlán Formation. Correlation of the 577 m composite magnetostratigraphic section with the Cande and Kent (1995) Geomagnetic Polarity Time Scale (GPTS) suggests that this section represents the time intervall 22.8–18.8 Ma (6Bn.1n-5Er; Aquitanian-Burdigalian, Lower Miocene). This correlation implies a deposition of the TF predating the extensive effusive activity in the TMVB at 12 Ma and is therefore interpreted to represent its initial phase with predominantly explosive activity. Additionally, three subdivisions of the TF were established, according to the dominant mode of deposition: (1) the fluvial dominated Malinalco Member (22.8–22.2 Ma), (2) the volcanic dominated San Andrés Member (22.2–21.3 Ma) and (3) the mass flow dominated Tepozteco Member (21.3–18.8 Ma).     

Identification of wetland water sources for environmental flow assessment: a case study of the Miguel Ibáñez wetlands (Segovia,Spain)

Abstract

This work aims to identify wetland water sources for environmental flow assessment of three wetlands located in the area of Miguel Ibáñez (Segovia, Spain), known as Fuente Santa, Balsa de la Ermita and San Pedro ponds. These are remnants of wetland systems that were larger in the past. The methodology used involved four seasonal field campaigns conducted in 2012 at eight main and three additional surface water or groundwater sampling points. The interpretation of the physico-chemical and isotopic data obtained, and daily monitoring of changes in the water level of the Fuente Santa pond over 5 months provided an initial understanding of the environmental flows needed to sustain these wetlands in appropriate conditions. The arsenic values provided an additional auxiliary tool, although a single dominant cause of its presence in these three ponds could not be identified. The results show that the interactions between the wetlands and groundwater are hydrogeologically different despite their proximity to one another. These findings will enable the improved management and conservation of these wetlands.

Editor D. Koutsoyiannis; Guest editor M. Acreman

Citation de la Hera Portillo, A. and Murillo Díaz, J.M., 2014. Identification of wetland water sources for environmental flow assessment: a case study of the Miguel Ibáñez wetlands (Segovia, Spain). Hydrological Sciences Journal, 59 (3–4), 466–487.