Cruise to the Incipient Rift

Emily Klein 'Mows' the East Pacific to Reveal Secrets of Magma p.2

Wax coring is “the most rudimentary way possible” to collect geological samples from the ocean floor, Klein acknowledged in a pre-expedition interview. On the other hand, “it’s fast, it’s cheap, you don’t have to bring a lot of equipment with you, and it’s very easy to do,” she added.

Geological specimens are like time machines, preserving evidence about the environment in which they formed. Flakes of black basaltic glass preserve a record of the chemistry of the lava at the moment that it suddenly “froze” after its passage from deep underground.

All but one of the 12 wax cores Klein retrieved from the Incipient Rift in 1999 contained fresh basaltic glass. After she brought those samples back she analyzed them with the aid of a special tool called an inductively coupled plasma mass spectrometer.

Bought with a grant from the National Science Foundation, which also funded Klein’s expedition back to the IR, the special spectrometer separates elements by the different weights of their isotopes with the aid of a powerful magnetic field. She could thus identify the different elements in the basalt, which provided vital hints about how lava was produced and changed during its upward journey.

The spectrometer study and other testing, “produced some tantalizing results for me,” Klein added. Particularly compelling was how concentrations of the element magnesium varied at her sampling spots along the rift.

Scientists believe the percentage of magnesium in a basalt sample’s makeup provides a benchmark for how much it physically and chemically “evolved” during its lengthy upward journey from the “mantle” region—a hot, high pressure netherworld about 7 kilometers below the ocean floor.

Until it erupts, lava is technically known as “magma” to geologists, who believe that the more a magma sample has cooled en route to the seafloor the lower its magnesium concentration. They reason that the “missing” magnesium would have been crystallized out and left behind.

Indirect clues such as magnesium levels are all scientists have to study what they can’t see: conditions in the deep extensive underground plumbing system that Nature uses to deliver fresh hot crust to repave the ocean floors.

One central question that Klein’s August expedition sought to address is how that magma is collected and channeled beneath the East Pacific Rise before it erupts there. Like popping a champagne cork, such eruptions are believed to release some of the pent up pressure in the mantle deep below. That causes some mantle material to rise and melt as it decompresses.

“It is now understood that melt comes from what is believed to be a very wide area of the mantle, something like 100 kilometers wide, and is being focused in a pyramidal shape towards the East Pacific Rise where it erupts,” Klein said.

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