Dive and Discover : Expeditions to the Seafloor

Dive & Discover’s 2nd voyage takes you about 500 miles south of Manzanillo, Mexico to the crest of the East Pacific Rise

, a volcanic ridge where the crust of the Earth is being constantly created. Seafloor spreading

is separating the Pacific Plate

from the Cocos Plate at a rate of 11 centimeters (about 5 inches) every year. Beneath the tropical waters of the eastern Pacific, there is a mountain range made up of many active volcanoes erupting lava

that forms the top 500 meters (about 1,640 feet) of the Earth’s crust. The lava flows have strange and wonderful shapes. Some look like they have been squeezed out of a tube of toothpaste to form long cylinders with deep grooves in them, others form big, cracked pillows of rock that look like overstuffed sofas; there are even lava flows that look like ropey swirls of black taffy.

How did these lavas form? When did they erupt? How do they build up to form the ocean crust

of the Earth? How are hydrothermal vents

, like the ones studied during Dive & Discover’s first cruise to the Guaymas Basin, related to these undersea eruptions and lava flows?

During Dive & Discover’s Cruise 2, scientists, engineers and students from several universities will use Alvin, armed with very sensitive instruments, to find out the answers to these questions. At night, while Alvin’s batteries are charging, they will also tow behind the ship a specialized camera sled which has a digital camera to take pictures of the volcanic seafloor. This will help them map the seafloor and understand how and where lava erupts deep in the ocean and how it builds up to form the ocean crust.

Research at this site on the East Pacific Rise got a boost in 1989 when Dr. Dan Fornari from Woods Hole Oceanographic Institution (WHOI) and Prof. Rachel Haymon of the University of California-Santa Barbara went to the crest of the East Pacific Rise between 9°N and 10°N Latitude to map the mid-ocean ridge

crest using a towed camera and sonar system called Argo [Click here to learn more about Argo]. On that cruise they found many hydrothermal vents and evidence for a large volcanic eruption

that covered several miles of the ridge crest with new, pillowy black lava. They went back in 1991 to dive at the East Pacific Rise crest to sample the hydrothermal vents and lava. What they found shocked them! When they dove to the seafloor in Alvin, they realized that there was a submarine volcanic eruption going on, and that hot, new lava had covered the seafloor, covering some of the hydrothermal vents they had seen just 2 years before with the Argo system, even cooking some of the tubeworms!

Now a team of geologists and geophysicists led by Dan Fornari and Jim Cochran of Lamont-Doherty Earth Observatory are returning to the East Pacific Rise with Alvin to study and sample the lava flows and hydrothermal vents. They will be using sensitive instruments to measure very small changes in the Earth’s gravity and magnetic fields to help them learn about the ocean crust and the lava that forms it. Just like a doctor using a stethoscope to find out what’s going on inside a human body -- medical remote-sensing -- Dan, Jim and their colleagues will be using geophysical remote-sensing to study the Earth’s ocean crust.

Join them as they explore the volcanic seafloor of the East Pacific Rise and try to understand what is underneath it -- inside the ocean crust, and monitor the biological and chemical changes at the hydrothermal vents since the 1991 eruption.

Objectives
What is Geophysics
Geophysics is the study of the Earth using the principles of physics. A geophysicist is someone who uses instruments to tell them about the Earth, rather than “seeing” it first-hand. These techniques, for example, using the speed of sound in different layers of the earth, or the study of Earth’s gravity and magnetic fields, help them to understand the internal structure of the planet. By using these methods, geophysicists have been able to tell what the “anatomy” of the Earth is. Geophysics is one of the most important methods for understanding where earthquakes take place and how to help prevent or minimize damage caused by them in cities like Los Angeles. Geophysics is also an important tool that helps scientists and engineers find oil and gas.

Looking into the Earth - Geophysics is the Key!
How do you see inside the Earth? On land, you can dig a trench to see the layers of sediment, look at the side of a cliff to see the layers of rocks and how they are folded, or go down into a mine to see the rocks inside the crust. At the mid-ocean ridge, looking inside the Earth is much more difficult. First of all, there are 2500 meters (8200 feet) of sea water between you and the rocks exposed on the seafloor. Alvin allows scientists to go down to the seafloor, make observations and sample the rocks, but getting information on what is below the seafloor is more difficult - you need different instruments and techniques to do that. That’s where geophysics comes in!

Objectives
Scientists on this cruise will use two different geophysical measurements to find out about the upper part of the ocean crust at the East Pacific Rise near 9° 37’N Latitude. The scientists are going to use two types of electronic instruments- one to measure small variations in the Earth’s gravity field and the other to measure small variations in the magnetic field along the axis of the East Pacific Rise. They will also be taking thousands of digital pictures of the seafloor using Alvin and a towed camera sled so that they can make detailed maps of the volcanic terrain and relate them to the gravity and magnetics. Together, this information, or data, will help them answer questions like these:

Hypothesis to Test
1. The pattern of dikes, or feeders that supply lava to the seafloor from the magma chamber underneath the East Pacific Rise axis can be mapped using gravity and magnetic data collected near the seafloor with Alvin.