Bottom characterization of Lagoa das Furnas on São Miguel, Azores archipelago

• High resolution geophysical mapping was made in Lagoa das Furnas.
• Geophysical mapping of Lagoa das Furnas reveals a previously undiscovered volcanic dome.
• The dome is suggested to be formed during a late phase of 1630 eruption.

Lagoa das Furnas is a crater lake located in an area exposed to geohazards from earthquakes and volcanic activity on the island of São Miguel in the Azores Archipelago. Geophysical mapping of Lagoa das Furnas reveals a previously undiscovered volcanic dome. This dome is comprised largely of subaquatic pyroclastic debris of trachytic composition. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the dome link it to the historically documented “Furnas 1630” eruption. The chemistry of glass and crystal fragments sampled from the dome suggests that it is comprised of more evolved magma than that of the main Furnas 1630 dome located 1400 m away. This suggests that the dome was formed during a final phase of the 1630 eruption in the Lagoa das Furnas area.