The October 2011 – March 2012 eruption was underwater, with a fissure of vents located approximately 2 kilometres (1.2 miles) to the south of the fishing village of La Restinga on the southern coast of the island.

[4] By the end of September, the tremors had increased in frequency and intensity, with experts fearing landslides affecting the town of La Frontera, and also a small possibility of a volcanic eruption through a new vent.

[citation needed] The main volcano on the island, Tanganasoga, underwent rapid inflation and increased carbon dioxide gas emissions, which were a cause for concern.

On 27 November the coast guard vessel Salvamar Adhara collected some pumice clasts,[10] colloquially nicknamed 'floating lava bombs' or 'lava balloons', some of many that had been ejected by the underwater eruption and floated to the surface of the sea before sinking again.

[11][12][13][14] In the following days, three scientific and seismic survey vessels studied the area: Sarmiento da Gamboa (bathymetry, gravity and mapping seismic profiles), Ramon Margalef (multibeam bathymetric survey, sediment sampling and the acquisition of echograms of the water column) and Cornide de Saavedra (physical and chemical evolution of the volcano stain).

[12] On 21 December 2011 it was suggested that the eruption was subsiding, as the harmonic tremors and earthquakes are decreasing in frequency;[16] however, in early January 2012 the earthquakes were increasing in frequency and the area of the eruption appeared to be increasing, with a wider area of sea producing the steaming pumice clasts, steam and general "jacuzzi" activity.

[12][20] Sensors measured that inflation of 4 centimetres (1.6 inches) height had taken place in the three days up to 27 June - a very fast rate of deformation.

[12][21] For the October 2011–March 2012 eruption, and the two phases of subsequent earthquake activity, plotting has shown that in all cases the magma rose under the area of Tanganasoga.

Modelling of ground deformation measured with radar interferometry confirmed two shallow magma reservoirs, consistent with the migration of earthquakes epicenters.