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Images: Paving the Seafloor—Brick by Brick

How is the seafloor paved with lava?
The development of ABE, the Autonomous Benthic Explorer, made it possible to fly close enough to the seafloor to measure magnetic intensities of young seafloor lava. Such measurements will give scientists the ability to unravel the convoluted processes by which lava carpets the seafloor. Scientists are investigating whether fresh lava (red) erupts from a central point in the mid-ocean ridge (as depicted above) and cascades downhill to overlay older lava flows (gray), or whether lava erupts from several isolated, outlying magma chambers to create discrete patches of seafloor. Or perhaps both processes occur.

By superimposing magnetic measurements on detailed seafloor topography maps like this one, scientists can distinguish how, when, and where individual lava flows occurred. Younger lava has the highest magnetic intensities (red and yellows). Above, the most recent lava flow erupted from the ridge axis, overlaid older lava flows, and pooled to the left of the axis.

Magnetic ‘zebra stripes’
Seafloor lavas have built-in magnetic “clocks” that reveal their age. When seafloor lava solidifies at the seafloor, its magnetic crystals are quenched in alignment with Earth’s magnetic field, and the rocks’ magnetic “polarity” is preserved. But Earth’s magnetic field has reversed many times over the planet’s history—with the magnetic north sometimes facing south, or vice versa, as it is today.
New seafloor is created at mid-ocean ridges (with the prevailing magnetic signature) and spreads out in both directions, creating a symmetrical “zebra-stripe” pattern of alternating rocks with either “reversed” or “normal” polarity.