Although traditional seismographs are essential for warning of earthquakes, they can be difficult to access when placed on the sea floor. Well, that's where the MERMAID underwater seismic floats are designed to come in, and they've recently been successfully tested in the Galápagos.

MERMAID is an acronym for "Mobile Earthquake Recording in Marine Areas by Independent Divers." The technology was first conceived of 15 years ago, by Princeton University postdoctoral researcher Frederik Simons (now a professor of geosciences) and Prof. Guust Nolet.

The floats take the form of cylindrical devices with adjustable buoyancy, that drift with the current at a default depth of around 1,500 meters (4,921 ft). Moving about 2 to 3 miles per day (3 to 5 km), they utilize an integrated hydrophone to listen for the sound waves associated with earthquakes.

When such sounds are detected by one of the MERMAIDs, it automatically uses an oil pump/bladder system to increase its buoyancy, rising to the surface within 95 minutes. It then determines its geographical location using GPS, after which it transmits its recorded data via satellite to shore-located scientists. Once they've analyzed that data, those scientists are subsequently able to determine the source of the sound waves. They can additionally transmit commands back to the MERMAID, such as instructing it to sink back down and continue listening.

By contrast, conventional marine seismographs sit immobile on the sea floor, and have to be manually pulled to the surface in order to relay their data.

As part of a recent international study, nine MERMAIDs were set adrift in the waters of the Galápagos for two years. Among other things, their readings allowed scientists to determine that volcanoes in the region are fed through a narrow conduit from a source 1,200 miles (1,900 km) deep. Known as a "mantle plume," the phenomenon was first proposed 48 years ago, but has proven difficult to confirm in various regions due to a lack of undersea seismic stations.

The team is now in the process of deploying 50 of the devices in the South Pacific, to study a mantle plume located beneath Tahiti.

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