Earth’s Tectonic Plates


Recovering ‘Sea Spiders’ and Heading Home

The NoMelt project is more than just a seismic experiment; it also has an important magnetotelluric (MT) component. MT instruments measure natural magnetic and electric fields on the seafloor, allowing scientists to estimate the electrical conductivity of the underlying rocks. Conductivity is highly sensitive to tiny amounts of water and molten rock within the upper mantle and thus can help distinguish whether the mantle is “wet” (and thus easy to deform) or “dry” (rigid and plate-like).

by |January 15, 2013

Santa Comes Bearing an OBS

Recovering OBS instruments from the ocean floor is always a tricky business, especially in our case; these instruments have been sitting beneath more than 3.5 miles of water for over a year. With cold, tired batteries powering the instruments’ acoustic transponders, communicating with them through miles of ocean currents amounts to a whispered conversation on a stormy night.

by |January 10, 2013
Calm seas and sunshine find the R/V Melville in the Pacific.

Transiting the Pacific

Today marks our sixth day aboard the R.V. Melville on a journey to a remote region of the Pacific to retrieve seismic instruments that have been quietly recording earthquake signals on the ocean floor for the past year. We have covered more than 2,600 km thus far but must cruise for another two and a half days before we reach the NoMelt project site.

by |December 30, 2012
Map displaying the NoMelt project site located ~1200 km southeast of Hawaii.

One Year Later – Return to the NoMelt Site

On December 18, 2012, the Research Vessel Melville departed San Diego to recover remainder of the NoMelt instruments and data. The expedition includes two scientists from Columbia’s Lamont-Doherty Earth Observatory: Post-doctoral scientist Patty Lin and graduate student Natalie Accardo. Natalie is sending regular reports from the ship.

by |December 30, 2012

Holidays on the High Seas

With round-the-clock shifts, there are precious opportunities for Santa to slip onto a research ship unseen. But slip in he did, leaving treats and gifts around the R.V. Langseth to brighten our day.

by |December 27, 2011
WHOI OBS is craned on board.

Retrieving Instruments from the Deep

Over the first 22 days aboard the R/V Marcus G. Langseth, we’ve zigged and zagged our way over a 360×240 mile region of the Pacific plate, first dropping instruments to the seafloor, and then shooting airguns to them (see previous posts). The final step is to recover a subset of the instruments:  34 ocean-bottom seismometers… read more

by |December 27, 2011
Float supporting a 9-gun array being deploy aft of ship.  Guns hang below float.  Yellow cables carry compressed air to three identical arrays previously deployed.

The Art of Sound in the Ocean

The NoMelt experiment aims to image the structure of an oceanic plate, including its deepest reaches up to 70 km beneath the seafloor.  One of our primary means to do so is to create sound (acoustic) waves in the ocean from the ship, and record those waves at receivers on the seafloor, after they have… read more

by |December 21, 2011
Short-period OBS being deployed by WHOI technicians.  Sensor and recording package contained within glass spheres in orange casing.   Anchor hangs from the bottom.

Deploying Instruments on the Seafloor in the Deep Ocean

Oceanic plates are born at mid-ocean ridges, where hot mantle rocks are brought very close to the surface, partially melt, and then cool and crystallize. The newly formed rocks move outwards from the mid-ocean ridge, making way for the next batch of hot rock rising from below. Inch by inch, over millions of years, oceanic… read more

by |December 13, 2011
The Langseth at dock in Honolulu.  Bridge cabins/labs are to the right; waist-deck where OBS operations occur is in the center; and the large aft streamer platform is on the left.  Top center is the PSO observation tower, over 85 ft above the waterline.

Rolling into Open Water in the Central Pacific

We nicknamed our project NoMelt because we seek to characterize a mature, pristine oceanic plate far from its volcanic origin at a Mid-Ocean Ridge, and away from areas of pronounced volcanism and melting that subsequently alter the structure of the plate.  Our site in the central Pacific fits these scientific needs. However, one downside is… read more

by |December 5, 2011
Google Earth map of the experiment (dubbed NoMelt) in the central Pacific Ocean basin.

Probing an Oceanic Plate

Everything that we understand about the rhythms of the Earth’s surface – the slow growth of mountain chains, the creeping expansion of the ocean basins, the abrupt upheaval of a major earthquake, the explosive eruption of a volcano – is viewed through the context of plate tectonics.  This simple yet highly successful model for describing… read more

by |November 30, 2011