Boomerang Seamount volcano (France) - shallow magnitude 4.8 earthquake

Source: Volcano Discovery - By T, 11/14/12

A shallow magnitude 4.8 earthquake occurred today under or near Boomerang Island, about 35 km NE from Amsterdam island (French territory) in the southern Indian Ocean.

It is unknown if the quake is caused by or related to volcanic activity, or whether some activity is actually occurring at the undersea volcano. The basaltic volcano rises to within 650 m of the sea surface and has a 2-km-wide summit caldera that is 200 m deep. Rift zones extend SE and north. Boomerang Seamount is one of several active volcanoes on the axis of the Southeast Indian Ridge.

The quake can be taken as a reminder that many volcanic eruptions from volcanoes on the sea floor go unnoticed. A submarine eruption from Boomerang volcano in this extremely remote location in particular would probably only be recorded if it is a major one, and even that is not to be relied upon: A probably large submarine eruption occurred in July / August this year from the until then unknown Havre Seamount in the Kermandec island chain NE of New Zealand. It was only discovered some weeks later, due to the appearance of large pumice rafts and by careful analysis of past satellite images, which revealed a plume.

The eruption of Havre, by the way, had also been closely preceded or were accompanied by a series of earthquakes of magnitudes around 5.0.