In the field area the sensors have to be buried to protect them from the disturbance of wind and weather and are left overnight (for broadband systems) or a couple of weeks (for long period observations) to record variations in the EM-fields. Using computer algorithms the collected data is then transformed into models of electrical resistivity that can image depths of about 50km, often represented in slices (for 2-D) or volumes (in 3-D). These models help us understand which processes are responsible for what happens on the surface of the Earth, i.e. the volcanic and seismic activity in the valley as well as the rifting process itself.