The HydroGeophysics Group has undertaken a large SkyTEM survey on Mayotte; a volcanic island between the African mainland and Madagascar. The survey is a part of an extensive investigation carried out by a close collaboration between the French Geological Survey, BRGM, the Mayotte Prefecture and the Aarhus University.

The purpose of the survey is three fold:

1. A geological map of the entire island has to be created. The airborne survey gives a full three dimensional picture of the subsurface and therefore it is an efficient tool for guiding the subsequent geological sampling and creation of the geological model.
2. At several locations there is a risk of landslides occurring when the soil gets very wet. It is possible to locate these areas using the survey results.
3. Most of Mayotte’s population is located along its extensive coastline. When the ground water resources are exploited, there is a severe risk that any aquifers will be destroyed due to salt water intrusion. Airborne EM is an efficient tool for mapping the salt/fresh water interface.

The technology
The SkyTEM system used in the survey had a transmitter moment of about 100 000 Am2. With this moment the maximum depth of investigation is up to 250m, while different geological layers are mapped right from the surface. The average line separation was 200m but some areas were flown with just a 100m separation. Data were processed while they were flown and the results were then used to optimize the location of the subsequent lines.

What happens right now?
The field work finished mid-November and right now geophysicists  from the HydroGeophysics group are processing and inverting the data to produce a 3D image of the entire island. State of the art algorithms in the Aarhus Workbench software package are used and the first results are promising.

Links
Mayotte island on Wikipedia

Where is Mayotte