2024-03-28T11:50:46Zhttp://digital.csic.es/dspace-oai/requestoai:digital.csic.es:10261/1902672019-11-12T12:02:28Zcom_10261_39226com_10261_8col_10261_39228
Gómez-Ortiz, David
Blanco-Montenegro, Isabel
Martin-Crespo, Tomas
Arnoso, José
Solla, Mercedes
Montesinos, Fuensanta G.
Vélez, E. J.
Calvo-Rathert, Manuel
Sánchez, Nieves
Lorenzo, Henrique
Soler, Vicente
2019-09-09T12:52:48Z
2019-09-09T12:52:48Z
2017-04-26
EGU General Assembly (2017)
http://hdl.handle.net/10261/190267
The Timanfaya National Park is a volcanic area in the southwest of Lanzarote Island (Canary Archipelago, Spain)
resulting from the 1730-1736 eruption period. Several active geothermal anomalies have been identified from
1970’s. Their location is important to prevent hazards in this restricted touristic area of the park. Presently, only
some regional geophysical studies based on gravity, magnetic and seismic data have been undertaken to model the
crustal structure of Lanzarote Island.
This work presents a new study about the geothermal anomalies in the Timanfaya National Park by the
analysis and joint interpretation of electrical resistivity tomography (ERT), magnetic anomalies and electromagnetic induction data (EMI). All analyzed data have been obtained over areas which had not been surveyed before.
The studied geothermal field is located at the Islote de Hilario visitor’s centre.
One 50m-long GPR profile was carried out in May 2012 along the location of a known geothermal anomaly
developed over pyroclastic deposits. The two main characteristics are: a) no continuous subhorizontal reflections
are displayed up to ∼12 m depth and, b) the intensity of the reflections varies laterally in good agreement with
the location of the geothermal anomalies (the higher the ground temperature, the greater the intensity of the GPR
signal). Thus, an outline of the subsurface area with higher temperatures can be observed, indicating that the
heat source is deeper at the beginning of the profile and extends laterally and progressively shallower towards
the end. Temporal variation of the shallow temperature distribution was also investigated by repeating the same
GPR profile in April 2015. Although both profiles look quite similar, subtle variations of the GPR signal intensity
suggest a certain temporal variation of the ground temperature.
In November 2012 a land magnetic survey was carried out in Timanfaya. In the Islote de Hilario area, total
field magnetic data were acquired with an Overhauser magnetometer following a 75m-long profile which
coincides in the first 50 m with the GPR profile. Three additional profiles (two of them parallel and one orthogonal
to the first one) completed the survey, allowing the interpolation of the data into a regular grid. The resulting
reduced-to-the-pole anomaly map displays some magnetic lows which could be related with high temperatures at
shallow depths causing the loss of magnetic properties within the subsurface volcanic rocks. Forward modelling
has been carried out to characterize the magnetic sources and to analyze the correlations with GPR data. These
models have been constrained with NRM and susceptibility data measured in the laboratory for samples from the
Timanfaya lava flows.
Preliminary results of EMI data show high resistivity areas in good agreement with the location of the
shallow geothermal anomalies, the magnetic lows and the high GPR signal intensity.
The comparison of the results obtained from the different techniques reveals that the joint interpretation of
ERT, magnetic anomalies and EMI methods provides reliable models useful for the location of shallow geothermal
anomalies. These non-destructive geophysical techniques are of crucial importance in areas of special protection
such as National Parks.
eng
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Identification of shallow geothermal anomalies in the Timanfaya National Park (Lanzarote, Canary Islands) through combined geophysical prospecting techniques
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