La Palma island (Spain) geothermal system revealed by 3D magnetotelluric data inversion

Abstract The study of geothermal systems is nowadays a topic of great importance because of the huge amount of energy that could be converted in electricity for human consumption from such sources. Among the various geophysical methods employed to study geothermal reservoirs, the magnetotelluric (MT) method is capable to reveal the internal structures of the subsurface and interpret the geological structures from the electrical resistivity. We present the first 3D resistivity model of La Palma (Canary archipelago, Spain) obtained from a dataset of 44 broadband magnetotelluric soundings distributed around the island. Our results highlight the presence of resistivity anomalies, spatially coinciding with density anomalies present in literature. In the north of the island, a high resistivity anomaly can be interpreted as the signature of an old intrusive body beneath the Taburiente caldera. In the south, a complex resistivity structure around the Cumbre Vieja volcanic ridge could be indicative of presence of an active geothermal system. In particular, low-resistivity anomalies, located in a high-fractured zone, have values compatible with clay alteration caps (illite and illite–smectite). Such a result suggests the presence of hot rocks, or a dike system, heating fluids in the interior of Cumbre Vieja volcanic system.

Download Full-text

Diffuse H2 and He degassing survey to study of hidden potential geothermal systems in La Palma, Canary Islands

10.5194/egusphere-egu2020-11218 ◽

2020 ◽

Author(s):

Fátima Rodríguez ◽

Antonio Polo Sánchez ◽

Katherine Dale ◽

Chloe Codner ◽

Alba Martín ◽

...

Keyword(s):

Rift Zone ◽

Average Distance ◽

Hydrothermal Systems ◽

Soil Gas ◽

Geothermal Systems ◽

Soil Matrix ◽

North West ◽

The North ◽

La Palma ◽

Cumbre Vieja

La Palma is one of the eastern islands of the Canary Archipelago located off the West African continental margin. Volcanic activity in the last 123 ka has taken place exclusively at the southern part of the island, where Cumbre Vieja volcano has been formed. Cumbre Vieja, one of the most active basaltic volcano in the Canaries, host seven historical eruptions being Tenegu&#237;a eruption (1971) the most recent one. Cumbre Vieja volcano, characterized by a main north&#8211;south rift zone 20 km long and covering an area of 220 km2, does not show any visible degassing that show the existence of active geothermal systems. For that reason, geochemical prospecting of soil gases and volatiles in the soil matrix itself of Cumbre Vieja can provide useful information to investigate the presence of permeable areas and potential upflow areas for the degassing of geothermal systems at depth.We report herein the results of an intensive soil gas study, focused on non-reactive and/or highly mobile gases such as helium (He) and hydrogen (H2), in Cumbre Vieja, with geothermal exploration purposes. He has unique characteristics as a geochemical tracer: it is chemically inert and radioactively stable, non-biogenic, highly mobile and relatively insoluble in water. H2 is one of the most abundant trace species in volcano-hydrothermal systems and is a key participant in many redox reactions occurring in the hydrothermal reservoir gas.Soil gas samples were collected at 1,201 sites selected from June 2019 to September 2019, with an average distance between sites of &#8776; 250 m, at &#8776; 40 cm depth using a metallic probe. He content was analyzed by means of a quadrupole mass spectrometer (QMS; Pfeiffer Omnistar 422) and hydrogen concentrations by a micro-gas chromatograph (microGC; VARIAN CP490). Soil He concentration showed values up to 23.9 ppm with an average of 5.73 ppm. Soil H2 concentrations measured ranged from typical atmospheric values (&#8776; 0.5 ppm) up to 19.8 ppm. The mean value measured for H2 was 0.78 ppm. Although He concentration values showed high spatial variability, the highest values can be observed in the north&#8211;south rift zone of Cumbre Vieja and around the surface contact with Cumbre Nueva ridge. Spatial distribution of H2 concentration showed the highest values in the north-west area of Cumbre Vieja volcano. The results showed here are useful to identify the possible existence of permeable portions of deep-seated actively degassing geothermal reservoirs. However, a multidisciplinary approach is essential to obtain additional information about possible geothermal systems underlying at Palma island with the last goal of the selection of appropriate locations for future exploratory wells.

Download Full-text

Far-Field Tsunami Impact in the North Atlantic Basin from Large Scale Flank Collapses of the Cumbre Vieja Volcano, La Palma

Pure and Applied Geophysics ◽

10.1007/s00024-015-1135-5 ◽

2015 ◽

Vol 172 (12) ◽

pp. 3589-3616 ◽

Cited By ~ 29

Author(s):

Babak Tehranirad ◽

Jeffrey C. Harris ◽

Annette R. Grilli ◽

Stephan T. Grilli ◽

Stéphane Abadie ◽

...

Keyword(s):

North Atlantic ◽

Large Scale ◽

Far Field ◽

Atlantic Basin ◽

North Atlantic Basin ◽

The North ◽

La Palma ◽

The North Atlantic ◽

Cumbre Vieja

Download Full-text

Identification of "WS" geothermal field system by analyzing TE, TM, and TE-TM of 2D magnetotelluric inversion models

Journal of Physics and Its Applications ◽

10.14710/jpa.v1i2.4660 ◽

2019 ◽

Vol 1 (2) ◽

pp. 41

Author(s):

Triana Triana ◽

Tony Yulianto ◽

Udi Harmoko ◽

Iqbal Takodama

Keyword(s):

Geothermal Field ◽

Reservoir Rock ◽

High Resistivity ◽

Geothermal System ◽

Magnetotelluric Data ◽

Low Resistivity ◽

A Value ◽

Te Mode ◽

Tm Mode ◽

Representative Model

Magnetotelluric data has been carried out at the "WS" geothermal field to analyze the resistivity model resulting from 2D inversion of magnetotelluric data in TE, TM and TE-TM modes. Base on the three models produced, the mode is determined to produce the most representative model to assist in the interpretation of the "WS" geothermal system. There is a step of modes separation, namely TE (Tranverse Electric) and TM (Transverse Magnetic) modes in processing MT data. Each mode produces a 2D model with different conductivity properties. The analysis results of the three modes explain that TE mode is dominated by low resistivity with a range of values of 10-35 Ωm and medium resistivity with a value range of 35-250 Ωm and a vertical resistivity contrast. The TM mode describes the high resistivity in the Southwest and the center of the track with a value of more than 470 sehinggam resulting in lateral resistivity contrast. While the TE-TM mode produces a model that is not much different from TM mode, only the distribution of the resistivity value is a combination with TE mode. This mode describes the distribution of resistivity both vertically and laterally. Based on the analysis of the three modes, it can be concluded that the TE-TM mode is the mode that produces the most representative model. Interpretation model shows that from the TE-TM mode we have a low resistivity distribution (10-35 Ωm) represent a cap rock zone, reservoir rock with a medium resistivity distribution (35-380 Ωm), resistive zone with a high resistivity distribution (more than 380 Ωm), and the existence of the three of faults structures ro be a controller system of the "WS" geothermal.

Download Full-text

Three-Dimensional interpretation of broadband magnetotelluric data at Fogo Volcano, Azores Islands

10.5194/egusphere-egu21-3403 ◽

2021 ◽

Author(s):

Colin Hogg ◽

Duygu Kiyan ◽

Volker Rath ◽

Andreas Junge ◽

Philip Hering ◽

...

Keyword(s):

Transfer Functions ◽

Jacobian Matrix ◽

Hydrothermal Systems ◽

Geothermal System ◽

Matrix Elements ◽

Renewable Energy Resources ◽

Magnetotelluric Data ◽

Volcanic System ◽

Northern Flank ◽

Fogo Volcano

The architecture of volcanic systems is essential to know as (1) it yields knowledge on evolution of the volcanic system, thus improving our capability to project future behaviour; (2) as it provides insights regarding geohazards (such as seismic activity, landslides, increased outgassing), crucial for mitigating risk to human population; (3) as it contributes to the assessment of potential for renewable energy resources. High electrical conductivity values are typically associated with volcanic-hydrothermal systems and the magnetotelluric (MT) method has proven to be successful in mapping such conductivity contrasts and constraining volcanic processses.The Azores archipelago (Portugal) is formed by nine volcanic islands located in the North Atlantic Ocean where the American, Eurasian, and African plates meet at a triple junction. S&#227;o Miguel Island is the largest of the archipelago and hosts three trachytic polygenetic volcanoes: Sete Cidades, Fogo (&#193;gua de Pau) and Furnas. Following our earlier MT studies at Furnas, 44 high-quality (to ~1000s) broadband MT sites were collected during 2018 across Fogo Volcano and the adjacent Congro region that is prone to seismic swarm activity.Our MT studies comprised two avenues: generating geoelectrical models that provided new insights into this unique setting, and investigating and assessing new tools for the MT community.(1) Fogo has a resistive core and we do not see a magma chamber beneath.(2) Shallow conductive channels are observed beneath Congro and their presence have been tested and validated through forward modelling and additional sensitivity tests.(3) The MT results can be used to map clay alteration, with the highly conductive zone on the northern flank of Fogo corresponding to the smectite zone. The alteration temperature distribution is consistent with the formation temperature recorded within the area.(4) A potential new geothermal resource has been identified. An area north of Ribeira Cha, on the southern flank of Fogo has very similar characteristics of the Ribeira Grande geothermal system that is located on the northern flank. This area may be key in increasing the energy self-sufficiency of the island. Depth slices through the final 3-D MT inversion volume will be presented.The new MT processing code of University of Frankfurt was compared against two long-standing codes commonly used in the MT community and it proved to yield superior responses for every site and examples will be presented. See presentation in this session &#8220;FFproc - an improved multivariate robust statistical data processing code for the estimation of MT transfer functions&#8221; (Castro et al).A novel approach exploiting the Jacobian matrix elements for the 3-D MT inversion strategy will be presented. The Jacobian matrix elements map the relationship between the model and model responses, thus portions of the model with low sensitivities infer that the sensitivity structure is algorithmically influenced more strongly by the regularisation term than by the data-fitting term. Our results will show that the computation of the Jacobian matrix (albeit computationally expensive) is a powerful tool in aiding interpretation.

Download Full-text

Geophysical characterization of the Menengai volcano, Central Kenya Rift from the analysis of magnetotelluric and gravity data

Geophysics ◽

10.1190/geo2011-0419.1 ◽

2013 ◽

Vol 78 (4) ◽

pp. B187-B199 ◽

Cited By ~ 2

Author(s):

Antony Munika Wamalwa ◽

Kevin L. Mickus ◽

Laura F. Serpa

Keyword(s):

Gravity Data ◽

Gravity Models ◽

High Resistivity ◽

Geothermal System ◽

Low Density ◽

Fracture Density ◽

Density Region ◽

Magnetotelluric Data ◽

Low Resistivity ◽

2D Resistivity

In this study, we qualitatively analyze detailed gravity and broadband magnetotelluric data in and surrounding the Menengai volcano of the East African rift in Kenya to assess geothermal potential of the region. Three-dimensional gravity models obtained by inverting residual gravity anomalies and 2D resistivity models obtained by inverting the transverse electric and transverse magnetic magnetotelluric modes show several common features. Our models show that a low-resistivity zone above a higher resistivity zone correlates with a low-density region located 1–4 km beneath the volcano. These zones may be related to a high temperature gradient or hydrothermally altered, fractured rocks. Additionally, a low-resistivity ([Formula: see text]) and a low-density region located approximately 4–6 km below the volcano may be related to molten material that is the source of heat for the geothermal system. The low-resistivity ([Formula: see text]) regions that correlated with a denser ([Formula: see text]) region within the caldera are bounded by high-resistivity ([Formula: see text]), high-density ([Formula: see text]) volcanic units implying that the dense and electrically resistive volcanic material is relatively cool and lacks significant fluid content that can lower resistivity. At shallow depths, 0.5–1.5 km below the caldera, a low-resistivity and low-to-moderate density region is interpreted as a zone with high fracture density that consists of clay minerals resulting from hydrothermal alteration. These results agree well with the results from previous seismic studies on the depth of the suggested molten rocks.

Download Full-text

Resistivity Models of Pantar Island Geothermal System East Nusa Tenggara, Indonesia

Journal of Geoscience Engineering Environment and Technology ◽

10.25299/jgeet.2020.5.3.5115 ◽

2020 ◽

Vol 5 (3) ◽

pp. 127-132

Author(s):

Yoqi Ali Taufan ◽

I. Syafri ◽

D. Risdianto ◽

A. Zarkasyi ◽

T. Rahadinata ◽

...

Keyword(s):

Heat Source ◽

3D Models ◽

High Resistivity ◽

Geothermal System ◽

Geothermal Systems ◽

Low Resistivity ◽

Resistivity Method ◽

Geological Conditions ◽

The Difference ◽

Clay Cover

The subsurface geological conditions of a geothermal system are vital objects to be considered in geothermal exploration. The Magnetotellurics survey was conducted to explore for geothermal potential in Pantar Island. This is to achieve deeper penetration compared to our previous study that adopted resistivity method to determine reservoir zones based on rock resistivity models. The difference in rock resistivity in geothermal systems provides subsurface geological information in the form of low resistivity that associated the clay cap zones (high conductive), the medium resistivity zones associated with the reservoir zones, and high resistivity associated with a heat source. The results of 2D and 3D models from MT data show that the low resistivity value (<20Ωm) as a clay cover zones, this layer from the surface to -1000 meters. Medium resistivity values (20-100 Ωm) starting from depths -1000 meters to -2000 meters associated with reservoirs zones, high resistivity values (> 200 Ωm) starting from depths of -2000 meters are considered as heat source from the Pantar geothermal system.

Download Full-text

Analysis of magnetotelluric data from Las Cañadas caldera (Tenerife, Spain)

10.5194/egusphere-egu21-12143 ◽

2021 ◽

Author(s):

David Martínez van Dorth ◽

Federico Di Paolo ◽

Katarzyna Slezak ◽

Iván Cabrera-Pérez ◽

Perla Piña-Varas ◽

...

Keyword(s):

Temporal Changes ◽

Geothermal Systems ◽

Geothermal Resources ◽

Magnetotelluric Data ◽

Volcanic System ◽

Subsurface Structures ◽

Phase Tensor ◽

Electric And Magnetic Fields ◽

Fluid Transfer ◽

Tectonic Features

Tenerife is the second-largest island in the Canarian archipelago with an area of 2034 km2. It consists of three ancient volcanic massifs (Anaga, Adeje and Teno) located at the edges of the island connected by rift zones to the centre of the island, in correspondence of Las Ca&#241;adas caldera. The caldera hosts the most relevant topographic element of Tenerife, the volcanic edifice of Teide &#8211; Pico Viejo. Previous studies already suggested the presence of geothermal resources inside and around the caldera. For this reason, in the present study, we have applied the magnetotelluric method (MT) in the central part of the island to better understand subsurface structures in this area.The MT method is a useful tool successfully applied to detect conductive and resistive structures located in the subsoil. It is commonly used in volcanic areas to detect volcano-tectonic features and geothermal systems to evaluate exploitable geothermal resources. Furthermore, continuous magnetotelluric measurements can also be employed for volcanic monitoring, allowing tracking temporal changes of the resistivity because of fluid transfer processes in the volcanic system.Between 2019 and 2020 we realised a detailed study of Las Ca&#241;adas caldera resistivity structure thought 45 magnetotelluric soundings. The instrumentation consisted of four Metronix ADU-08e, equipped with EPF-06 electrodes and MFS-06e magnetic coils, which registered electric and magnetic fields along the N-S and E-W directions. We also installed three remote stations at different times inside the caldera. Depending on the station quality, we obtained the MT response functions for periods of 0.001 &#8211; 1000 s. The dimensionality of the data has been analysed using the phase tensor. &#160;The first preliminary results of dimensionality and strike analysis indicate a 1D/2D behaviour for the first layers which present a decreasing resistivity, evolving to a 3D behaviour from 1s and with an increase of resistivity with depth.Furthermore, we present some results obtained by a permanent MT station to check the possibility of temporal changes in the electrical resistivity. During the time this station was recording two electrical blackouts which took place on the island. This allowed quantitatively estimating the level of anthropogenic electromagnetic noise in the recorded time series.

Download Full-text

Soil gas CO2 concentration, isotopic ratio and efflux measurements for geothermal exploration at Cumbre Vieja volcano, La Palma, Canary Islands

10.5194/egusphere-egu2020-1164 ◽

2020 ◽

Author(s):

Alba Martín Lorenzo ◽

Banner Cole ◽

Elizabeth Bullock ◽

Sahlla Abassi ◽

Lía Pitti-Pimienta ◽

...

Keyword(s):

Canary Islands ◽

Soil Co2 Efflux ◽

Soil Gas ◽

Geothermal System ◽

Co2 Efflux ◽

Soil Co2 ◽

Geothermal Exploration ◽

Diffuse Degassing ◽

La Palma ◽

Cumbre Vieja

The exploration of geothermal resources on the island of La Palma, Canary Islands, was first conducted by the Spanish Geological Survey (IGME) from 1982 to 1984. These studies were focused exclusively on the southern part, where the last historical eruption, Tenegu&#237;a, took place in 1971. This area still shows some geothermal features such us relatively high ground water temperatures (about 40&#186;C) and soil CO2 efflux values. Recent studies carried out at Cumbre Vieja volcano, the southern part of the island, on diffuse degassing, 3D gravimetry and Audio-MT probes point to promising results, although more studies are needed. We continue applying a multidisciplinary approach to obtain additional information about the geothermal system underlying at Palma island using novel techniques as well as tools which are appropriate to evaluate this system. For this reason, during summer 2019 a soil diffuse degassing research started at Cumbre Vieja volcano (220 km2) for geothermal exploration purposes. In this first phase of the diffuse degassing study about 1,200 sampling sites, with an average distance between sites of approximately 250 m were selected after taking into consideration the volcano-structural features and accessibility. In each sampling site in-situ soil CO2 efflux measurements were performed, and soil gas samples were collected at 40 cm depth for chemical and isotopic analysis. Spatial distribution of CO2 efflux, statistical-graphical analysis of CO2 efflux, and &#948;13C-CO2 isotopic data to calculate and map the volcano-hydrothermal contribution of CO2 were combined and used for geothermal exploration. The statistical-graphic analysis of the diffuse CO2 efflux values confirms the existence of different geochemical populations showing two log-normal geochemical populations, a fact that suggests the addition of deep-seated CO2. Relatively low CO2 efflux values were measured ranging from non-detected up to 72.8 g m-2 d-1, with an average value of 4.6 g m-2 d-1. The highest CO2 efflux values were measured at the north end of Cumbre Vieja, around the surface contact with Cumbre Nueva ridge. The CO2 isotopic composition, expressed as &#948;13C- CO2 showed the contribution of three different end-members: biogenic, atmospheric and deep-seated CO2. The results indicate that most of the sampling sites exhibited CO2 composed by different mixtures between atmospheric and biogenic CO2 with slight inputs of deep-seated CO2, with a mean value of -15.3&#8240;, being the maximum and the minimum -2.8&#8240; and -25.4&#8240; respectively. The results showed here can help to identify the existence of zones where deep-seated actively degassing from geothermal reservoirs occurs, particularly where the interpretation and application of geophysical data might be difficult.

Download Full-text

Geochemical monitoring of Cumbre Vieja volcano (Canary Islands) by summer diffuse CO2 degassing surveys

10.5194/egusphere-egu2020-11386 ◽

2020 ◽

Author(s):

Daniel Di Nardo ◽

Ellie-May Redfern ◽

Filippo Zummo ◽

Alba Martín-Lorenzo ◽

Claudia Rodríguez-Pérez ◽

...

Keyword(s):

Volcanic Activity ◽

Sequential Gaussian Simulation ◽

Surveillance Program ◽

Volcanic Gas ◽

Distribution Maps ◽

The North ◽

La Palma ◽

Seismic Swarms ◽

Gaussian Simulation ◽

Cumbre Vieja

La Palma Island is the north-westernmost and one of the youngest of the Canarian Archipelago. In the last 123ka, volcanic activity has taken place exclusively at Cumbre Vieja volcano which is located at the southern part of the island. Cumbre Vieja is characterized by a main north&#8211;south rift zone 20km long and 1950m in elevation covering an area of 220km2 with volcanic vents located northwest and northeast. Cumbre Vieja is the most active basaltic volcano in the Canaries with 7 historical eruptions, being Tenegu&#237;a (1971) the most recent one. The most relevant volcanic activity episodes occurred since Tenegu&#237;a eruption, are two intense seismic swarms occurred beneath Cumbre Vieja on 7-9 and 13-14 of October 2017. Since visible volcanic gas emissions do not occur at the surface of Cumbre Vieja, the geochemical surveillance program has been focused mainly on diffuse degassing studies. In the last 18 years diffuse CO2 emission surveys have been yearly performed in summer periods to minimize the influence of meteorological variations. Measurements have been performed following the accumulation chamber method in about 600 sites and spatial distribution maps have been constructed following the sequential Gaussian simulation (sGs) procedure to quantify the diffuse CO2 emission. Herein we summarize the diffuse CO2 emission time series during this period and describe the results obtained in the last 2019 survey. The soil CO2 efflux values measured in 2019 survey ranged from non-detectable to 72.7gm&#8722;2d&#8722;1. Diffuse CO2 output was estimated in 1,064 &#177; 35td-1, a value within the background +1s range (1,254 td-1) (Padr&#243;n et al., 2015, Bull. Volcanol. 77:28). In the period 2001-2017, the diffuse CO2 output released to the atmosphere from Cumbre Vieja volcano ranged between 320 to 1,544td-1. Enhanced endogenous contributions of deep seated CO2 might have been responsible for the higher CO2 emission values measured in 2011 and 2013. After the October 2017 seismic swarms, diffuse CO2 output showed an increasing trend from 788 to 3,251td-1 in March 2018, to decrease gradually until 852td-1 in September of that same year, and begin to gradually increase again to 2,371td-1 in November 2018. These changes were possibly caused by an upward magma migration. Our results demonstrate that periodic surveys of diffuse CO2 emission are extremely important for the detection of early warning signals of future volcanic unrest episodes at Cumbre Vieja.

Download Full-text

State‐of‐the‐art geophysical exploration for geothermal resources

Geophysics ◽

10.1190/1.1441889 ◽

1985 ◽

Vol 50 (12) ◽

pp. 2666-2696 ◽

Cited By ~ 55

Author(s):

Phillip. M. Wright ◽

Stanley H. Ward ◽

Howard P. Ross ◽

Richard C. West

Keyword(s):

Hard Rock ◽

Geophysical Methods ◽

Well Logging ◽

Geothermal System ◽

Geothermal Systems ◽

Depth Of Penetration ◽

Thermal Methods ◽

Geothermal Resources ◽

Industrial Processing ◽

Stage Of Development

At the present stage of development, use of geothermal energy saves about 77 million barrels of oil per year worldwide that would otherwise be required for electrical power generation and direct heat applications. More than a dozen countries are involved in development of geothermal resources. Currently, only the moderate‐ and high‐temperature hydrothermal convective type of geothermal system can be economically used for generating electric power. Lower‐temperature resources of several types are being tapped for space heating and industrial processing. Geophysics plays important roles both in exploration for geothermal systems and in delineating, evaluating, and monitoring production from them. The thermal methods, which detect anomalous temperatures directly, and the electrical methods are probably the most useful and widely used in terms of siting drilling targets, but gravity, magnetics, seismic methods, and geophysical well logging all have important application. Advances in geophysical methods are needed to improve cost effectiveness and to enhance solutions of geologic problems. There is no wholly satisfactory electrical system from the standpoint of resolution of subsurface resistivity configuration at the required scale, depth of penetration, portability of equipment, and survey cost. The resolution of microseismic and microearthquake techniques needs improvement, and the reflection seismic technique needs substantial improvement to be cost effective in many hard‐rock environments. Well‐logging tools need to be developed and calibrated for use in corrosive wells at temperatures exceeding 200°C. Well‐log interpretation techniques need to be developed for the hard‐rock environment. Borehole geophysical techniques and geotomography are just beginning to be applied and show promise with future development.

Download Full-text