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Recent and Current Field Experiments

by GIBERT Dominique - 30 September 2007

- October 2007: One more electrical tomography experiment is scheduled for this month. Participating people are Dominique Gibert , Florence Nicollin and Bruno Kergosien. They will join François Beauducel and other members of the Volcanological observatory to perform an experiment of geo-electrical "mise-à-la-masse" where a current electrode is placed inside a conducting body. This method was initially designed in mineral mining and, in the present instance, the conducting body is the acid reservoir connected to the Tarissan pit. A first experiment if this kind was performed in June 2006 and the purpose of the present mission is to augment the data set.
- March 2007: The line of temperature probes placed in the Tarissan pit is about to be removed and brought back to the Obversatory. Several probes give spurious signals, probably due to alteration by both temperature and acid. Since November 2006, the data are recorded with and IDL100 data logger (Gantner - BGP Electronic) at a sampling rate of 10 seconds. This is sufficient to capture the low-frequency components, and particularly the tide signals detected in the first data of October 2006.
- February 2007: The Tarissan geophysical station has totally been upgraded by Christian Antenor-Habazac and Thierry Kitou in order to secure both the power supply with solar pannels and the protection against both heavy rains and acidic gasses coming from the Tarissan pit.
- October 2006 : Dominique Gibert will be on-site from October 2th to October 27th. The objectives of the mission are to repair the temperature sensor of the cable placed in July and to put a second cable equipped with a new temperature probe in the Tarissan pit. This cable is being prepared by Jacques Grangeon in the Chambery lab. Another cable with 12 temperature probes will also be place in the steam panache of the Tarissan pit in order to monitor the turbulent activity. A new data logger with a 1 kHz maximum sampling rate will be used. Exploratory investigation, using rope access techniques, are planned to recover the Spallanzani cave beneath the Fente du Nord and an exploration of the Cratère Sud (estimated depth 120 m) is also scheduled.
- August 2006: the July mission is completed and the cable was successfully placed in the Tarissan pit by august 1st just before a tropical storm alert. The acid lake at the bottom of the pit was daily sampled during 10 days and the temperature was measured at 7 levels (from -60m to 0 m relative to the Pont Naturel level) in the vapor cloud during 5 days.
- July 2006 : A two-week mission is planned, starting july 23th, for a couple of experiments in the Tarissan pit. A new cable carrying an hydrophone, a thermistance and a pressure gauge will be placed in the lake of boiling acid. This cable will be connected to a telemetry station placed near the pit. Also, a cable equipped with 8 temperature sensors (pt100) will be temporarilly placed in the pit to monitor the activity of degassing. Contacts: Dominique Gibert and François Beauducel for field operations, and Jean Vandemeulebrouck for details concerning the design of the cable and monitoring of hydrothermal systems.
- June 2006 : A new electrical tomography campaign is planned for june of 2006. The objectives of this mission is to make new tomography profiles in the northwestern part of the lava dome, where a landslide caused by Les Saintes earthquake (november 2004 ) made the field clear of vegetation. Contact: Dominique Gibert .
- March 2006: A campaign of CO2 flux measurement started in the middle of March 2006 with Patrick Allard and his colleagues from the Guadeloupe Volcanological Observatory and from Italy. The experiments consist in measuring the CO2 emanating from a surface of soil of about a quarter of a squared meter. The campaign should be completed by the end of March 2006.
- February 2006: Spontaneous potential mapping of La Soufrière area by Jacques Zlotnicki and colleagues from University of Toulouse. This experiment is also finished and the staff returned to France. Data will now be processed and results are expected by the end of year 2006.
- February 2006: Seismic tomography of La Soufrière dome by Olivier Coutant and colleagues from University of Grenoble (LGIT). Last informations dated saturday, february 18th, indicate that this experiment is now completed. The equipment is being removed from the field and the staff now download the data by using the radio link between the seismological stations kept on the field and the volcanological observatory. The meteorological conditions were fine during the field operations and the helicoptere was used for equipment transport onto the volcano. Last news (25 feb 2006) indicate that the data downloading was successfully done through the WIFI connection between the volcanological observatory and the seismological stations on the field.