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Images: The Quest for the Moho

Atlantis Bank on the Southwest Indian Ridge was targeted for drilling because much of its upper crust has eroded away, leaving the Moho closer to the surface. (Base map: SIO, NOAA, U.S. Navy, NGA, GEBCO; Image Landsat Data: LDEO-Columbia, NSF, NOAA)
Atlantis Bank formed as the Southwest Indian Ridge spread apart. A huge block of deep-ocean crust slid up to the surface over 26 million years along the ramp of a tectonic fault. It’s an ideal location to try to drill to the Moho, the boundary between Earth's crust and mantle, because there are no upper-crust basalts and dikes to drill through. (Illustration courtesy of Henry Dick, Woods Hole Oceanographic Institution)
In 1989, WHOI geologist Henry Dick led an expedition that drilled Hole 735B 1,640 feet deep into lower-crust gabbro rocks. In 2016, he returned to drill Hole U1473A, the first phase of a project to try to drill into serpentine and mantle rocks above and below the Moho. Phase II will use the mammoth Japanese drillship Chikyu. (Illustration courtesy of Henry Dick, Woods Hole Oceanographic Institution)
WHOI geologist Henry Dick examines cores during his most recent effort to drill the first hole through Earth’s ocean crust and the Moho to extract an unaltered sample of rocks from Earth’s mantle. (Photo by William Crawford, IODP, Texas A&M University)
Crew members aboard the JOIDES Resolution drillship connect drill pipes beneath the ship's derrick. A re-entry cone installed on the seafloor helps guide the tip of a drill pipe into the hole being drilled through the ocean crust toward the Moho. (Photo courtesy of the Ocean Drilling Program)
A re-entry cone installed on the seafloor helps guide the tip of a drill pipe into the hole being drilled through the ocean crust toward the Moho. (Photo courtesy of the Ocean Drilling Program)
The tungsten drill bit at the tip of the drill pipe has four mace-like heads to bore through ocean crust. But three broke off during drilling in 2015. (Photo by William Crawford, IODP, Texas A&M University)
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