In the second of the three lava flows, dating from about 150,000 years ago, it is where a lava tunnel was identified that the colada created when flowing through this area. What can be seen are fragments of the walls of the tube that, in the inner zone, have been re-filled by sediments dragged by the river. The overpressure of the large amount of lava that circulated through this tube caused a deformation, or blister (bubble), on the roof of the tunnels, generating small mounds in the laundry. The erosion of the Fluvià River, in the Molí Fondo area, has revealed these unique formations throughout the Iberian Peninsula.