Magazine article Oceanus

From the Beginning: Monitoring Change in a Young Lava Flow

Magazine article Oceanus

From the Beginning: Monitoring Change in a Young Lava Flow

Article excerpt

A unique opportunity to monitor changes in a seafloor lava flow nearly from its inception began in the summer of 1993. Just days after National Oceanic and Atmospheric Administration scientists activated a new real-time earthquake monitoring network, seismic activity was detected on the Juan de Fuca ridge in the northeast Pacific. This activity indicated that an eruption was underway, and research vessels were dispatched to locate it. The eruption, which formed a lava flow 30 meters thick, 1,500 meters long, and 300 meters wide, was fed from what is thought to be a subsurface feeder dike (a fissure that serves as a conduit from a body of molten material to the seafloor). Using conductivity-temperature-depth instruments, scientists aboard research ships were able to detect hot water plumes from vents created by the cooling lava as it heated the seawater. Echosounding ships repeating previous mapping tracks also recorded a difference in the depth of the sea-floor where the lava flow had erupted. Together the diking event and lava flow represent the basic building block of oceanic crust - by investigating this newly emplaced seafloor feature we can better understand the process by which almost 70 percent of Earth's surface has formed.

The physical properties of the new lava are still pristine, and knowing the precise age of the rocks allows us to monitor their changes over time. One important property is magnetism and new lava turns out to be highly magnetic. As the molten lava is rapidly "quenched" or cooled on contact with seawater, the magnetic minerals it contains quickly "freeze," recording the direction and strength of Earth's magnetic field, which varies over time. …

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