Dive and Discover : Exp. 8 : Juan de Fuca Ridge : Daily Updates

Imagine driving a small car at night through an unfamiliar mountain range, equipped with only a flashlight to guide your way among the valleys and peaks. Without seafloor maps, flying in the research submersible Alvin at hydrothermal

vent fields on the Endeavour Segment would be just as tricky.

A major objective of this expedition is to create high-quality maps of the Main Endeavour and Mothra hydrothermal vent fields. Maps help researchers plan their explorations of the seafloor by pinpointing specific chimneys, fissures, and valleys of interest. They also ensure that researchers aren’t flying aimlessly among these complex seafloor structures, which would be frustrating, as well as a waste of time and money.

To explore the Main Endeavour vent field, scientists and Alvin pilots have been using maps developed by Marine Geologist Veronique Robigou at the University of Washington during previous Alvin dives to the field. Scientists on this cruise are developing even more detailed maps using a near-bottom, high-frequency scanning sonar

. This measurement can "see" details on the seafloor smaller than 3 feet (1 meter), which is many times better than the sonar collected from the surface ship. Maps made from Alvinmeasurements are sharper and clearer because they are made closer to the bottom—50 feet (15 meters) off the bottom, compared to the ship at more than 1 mile (1.6 kilometers) above the bottom—and because the Alvin measurements are made at a higher frequency, 675 kilohertz compared to 12 kilohertz from the ship.

Today researchers in Alvin dove to a northern portion of the Main Endeavour field called Hulk, named for its tall, tree-like black smoker

chimneys. Researchers had mounted the Imagenex system under the rear of the sub, and the sub flew slow, tight loops about 50 feet (15 meters) above the field. The sonar swept back and forth in continuous arcs, sending pulses of sound that bounced from the chimneys and other features back to the sonar system. The time for each sound pulse to return to the system is used to calculate the depth and location of the seafloor features.

STITCHING TOGETHER A MAP
Hundreds of thousands of these data were collected in a data logger on the sub, and when Alvin returned to Atlantis about 4 p.m., Technician Dave Sims downloaded the information to the ship’s computers. Tonight Geological Oceanographer Vicki Lynn Ferrini will begin processing the data, which she will sort and compile to begin creating seafloor maps.

The data are also valuable to Deb Glickson, a doctoral student at the University of Washington, who uses the maps to better understand the geologic processes that created the Main Endeavour and Mothra vent fields.

In the days ahead we will return to the Mothra field, which is still largely unexplored since its discovery in 1996. Researchers know it as the largest field on the Endeavour Segment, stretching the length of six football fields, nearly a half mile. So far on this expedition, they have half of the field mapped, and with one more dive, they should have enough data to nearly complete the job.