Living Atop the Volcano
Pam Eastlick for THE DEEP on line

Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.

Virtually all of us know that we live on the Pacific Rim in the most seismically and volcanically active area on the planet. The Pacific planet is plunging beneath Asia and the light seafloor basalt seeks its way back to the surface to form the Ring of Fire.

We’ve talked about Anatahan, the active volcano to the north of Saipan and most of us remember when Pagan blew its top in the 80’s, but I suspect that most of you didn’t know that ALL the islands north of Saipan (with one exception) are considered active volcanoes. 

But the northern islands are only the ones that have managed to get their heads above water. There are a whole host of undersea volcanoes south of Saipan, including Esmeralda, 30 miles due west of Tinian and Saipan and Mount Tracy, about 15 miles off the northwest bow of Guam. Our great earthquake originated in yet another unnamed volcano very close to Guam. Esmeralda is about to break surface but the others are much farther from ‘island status’.

Image courtesy of Submarine Ring of Fire 2006 Exploration, NOAA Vents Program

There has been a recent research expedition that made national news. This one was to an undersea vent very close to home. The Submarine Ring of Fire 2006 expedition sponsored by NOAA visited our area and found some remarkable things. The Jason II robot explored NW Rota 1, a volcano about 40 miles northwest of Rota and discovered active vents including one they named the "Brimstone Pit". This one was discharging a "pulsating, opaque, yellowish smoky plume with characteristics unlike any known hydrothermal plumes." The plume would fluctuate in volume and intensity, punctuated by explosions of sulfurous clouds. In 2005, the volcano showered Jason II with volcanic "bombs," 6-inch globs of semi-molten sulfur and debris that shot upward 150 feet from Brimstone Pit.

One of the researchers, Bill Chadwick, a geologist at Oregon State University and the NOAA Vents Program, said that although the eruptions could be violent, they were usually confined to a small area because Brimstone Pit is in almost 2000 feet of water. The great pressure slows down the rocks and ash that are tossed out of the pit. Most of the time, the underwater robot Jason could hover about 10 feet away and watch for hours. “You could never do that on land," he said. "We could also see the release of volcanic gases from the erupting lava with new clarity with the help of the streams of bubbles and multicolored plumes as they were emitted."

The science team also found microbial mats and hydrothermal vent-dependent animals on Rota, including two different species of vent shrimp in huge numbers. This year, they found that at least one of the shrimp species was supplementing its diet by eating dead mid-water fish that fell to the seafloor -- apparently killed by the toxic cloud above the volcano. (Esmeralda has long been known to local fishermen because the ‘sulfur boils’ above it produce huge numbers of dead fish.) While much of the focus has been on Rota, because of its recent volcanic activity, the researchers have surveyed more than 50 submarine volcanoes in the Mariana arc. At some of the sites they observed in 2004 using an ROV, they discovered black "smokers" -- chimneys made from spewing minerals and hydrothermal vents. .

Most such vents are deep in the ocean, but they found some on the shallow summits of volcanoes with schools of tropical fish, tuna and sharks swimming nearby.

Ring of Fire 2006 also explored two active volcanoes due west of Guam. Both of them are virtually on top of the back arc spreading center axis, the source of new volcanism in the Marianas. They are both very deep; their tops are still 4,000 feet of water. The researcher found that Seamount X, the first volcano they visited was crawling with vent life like shrimp, crabs, and scaleworms. Near the end of the dive they found a huge deposit of sulfur that was covered with thousands of lobsters. They don’t know why the sulfur attracts them but they suspect that they may be feeding on microbial mats growing on their own bodies. The researchers also visited Forecast Seamount, located just 10 miles away from Seamount X. There they registered hydrothermal fluid temperatures up to 400°F, one of the highest temperature vent systems ever discovered in the Mariana Arc. No wonder these undersea volcanoes have a reputation for cooking fish!

As I learn more about these volcanic wonders in my very own backyard (literally!) I am reminded of the song "A Horse with No Name," by the rock group America that contains the line "The ocean is a desert with its life underground, and the perfect disguise above. ... A glance at the map that accompanies this article, will certainly give you a whole new perspective on what lies beneath that deceptively flat ocean surface!

For a much more in depth look at the volcanoes next door, visit NOAA's OceanExplorer Web Site.