Explore the Deep Sea

Volcanoes & Vents

Recent Discoveries & Highlights

Some of the latest scientific news about mid-ocean ridges and hydrothermal vents.

Gala in the Galápagos

Scientists Celebrate the 30th Anniversary of Deep-Sea Vent Discovery

The Galápagos Islands are famous as the home of beautiful blue waters, dramatic mountains, and unique plants and animals (the same ones that helped to shape Charles Darwin's theory of 'natural selection'). But these islands also hold a special place in the history of hydrothermal vent exploration: In 1977 scientists discovered the first volcanic hot vent on the seafloor, just north of the islands. Since then, nearly 100 vent sites have been found in the deep waters of the global ocean, and the search continues today to find even more.

Just as thrilling as the discovery of the vents themselves was the discovery of bizarre animals found thriving around them in total darkness: six-foot-long tubeworms, dinner plate-sized clams, and ghostly-white crabs. Before this discovery, scientists had not even imagined that animals could live in such a cold, dark and deep environment - so far away from the energy of sunlight!

This past June, an international team of about 50 scientists traveled to the Galápagos Islands to mark the 30th anniversary celebration of the first vent discovery. "The discovery of hydrothermal vents remains one of the most exciting discoveries in the past century," said Dr. Paul Tyler. Along with many other scientists, Dr. Tyler is involved in documenting all of the ocean's life by 2010 as part of a program called the Census of Marine Life. Although many kinds of life in the ocean have been familiar to people for thousands of years, others like those discovered at hydrothermal vents have only been revealed to us in the past few decades. And it is believed that many more species, from tiny plankton to larger fish, may still remain undiscovered...

The local people of the Galápagos (known as Galapagoans) also had a chance to celebrate the anniversary and learn more about the vents near their special islands. Visitors enjoyed presentations from scientists about the vent discoveries, viewed the large-screen film "Volcanoes of the Deep Sea", and interacted with a display that included a deep-sea tubeworm anatomy station.

Funding for the meeting was provided by the Alfred P. Sloan Foundation.

Podcasts of the talks by Dr. Fred Grassle of Rutgers University and Emory Kristof of the National Geographic are available to download.

More information about the discovery of vents is available in this PDF, "Through the Porthole 30 Years Ago."

Learn more about the program that organized the Galápagos meeting (ChEss) and other deep-sea research programs (InterRidge, Ridge 2000) that also provided support.

Images courtesy of ChEss

 

A sound idea for mapping plumes

Like smoke billowing out of a factory chimney, hot fluid gushing from a deep-sea hydrothermal vent forms a buoyant plume that rises upwards into the overlying ocean. As it rises, the vent fluid mixes with, and is cooled by, the surrounding seawater. At a certain height above the seafloor — often 100m (330 feet) or more — the cooling fluid's density matches the seawater's density and the plume no longer rises. Instead, it drifts sideways with the currents, still cooling and mixing with the seawater. The upper part of a plume can sometimes be detected hundreds of meters away from a vent.

Diagram showing a plume rising from a vent at a mid-ocean ridge.

Scientists are interested in tracing the routes taken by hydrothermal plumes, for several reasons. For example:

So how can scientists map the extent of a plume and study how it moves? Not by shining light on it — in the deep sea, light is quickly absorbed and only illuminates a few meters at a time. So a team of scientists, (Dr Peter Rona and Dr Karen Bemis of Rutgers University with their partners at the Applied Physics Lab of the University of Washington) have adopted a new approach — they don't watch for plumes, they listen for them.

Well, they don't actually listen with their ears. Instead, they use a technique called acoustic imaging. Sound travels through water much better than light does. Acoustic (sound) waves sent through water will bounce (or "echo") off particles or obstacles and can be detected as they return. Sound waves bounce off the abundant metallic particles found in plumes, allowing scientists to map the shape and location of the plume, and learn how fast it is flowing.

Using this technique, the scientists have mapped a major hydrothermal plume from the "Grotto" vent on the northern Juan de Fuca Ridge (in the northeastern Pacific Ocean, off the coast of Washington State). They found that the plume changes direction along with the tides, even though it levels off more than 2km (7000 feet) below the sea's surface. In future, the scientists will use the same technique to monitor how plumes are affected by tides, earthquakes, and seafloor volcanic eruptions — over time periods from hours to years.

Their findings are published in Geophysical Research Letters.

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Mystery of the missing salt

The fluid emitted by deep-sea hydrothermal vents originally starts life as seawater that sinks down into seafloor rocks through cracks and fissures. As it gets deeper, it heats up and its chemical make-up changes — for example, as minerals from surrounding rocks dissolve in it. Eventually, the altered fluid moves upwards again, to emerge through a vent (such as that pictured here).

Billow of minerals precipitating out above a hydrothermal vent. Image courtesy of C.Fisher.

Intriguingly, many vents spew out fluid that is less "salty" (saline) than seawater. For instance, at the Juan de Fuca Ridge, some vents have been emitting low-salinity fluid for years. Given that vent fluid is derived from seawater, where has all the missing "salt" gone? Scientists think that it is accumulating and circulating within the rocks of the crust. But how, exactly?

One possibility is that brine — fluid very rich in salt — somehow accumulates in a "deep brine layer" deep in the Earth's crust. But there is a problem with this idea. Measurements at the Juan de Fuca mid-ocean ridge suggest that any such layer must be at least 100m thick, given the quantity of missing salt. However, other calculations suggest that a brine layer can't possibly be this thick because the system is so hot.

Now two University of Washington scientists have suggested an alternative way in which salt-rich fluid can accumulate in crustal rocks, even in hot systems like the Juan de Fuca ridge. They propose that — rather than pooling in a separate layer below less salty water — the brine sits in tiny cracks within the crustal rocks, a bit like water sits inside the pores and crevices of a sponge. So this salt-rich fluid is effectively held within the rocks while the less salty water flows through the larger cracks, and out into the ocean through vents.

Their idea is published in a June 2006 issue of the Journal of Geophysical Research.

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How oceanic crust is formed

At mid-ocean ridges, magma (molten or partially-molten rock) crystallizes to form new crust. Given that the oceanic crust can be 3-5 miles (5-8 km) thick, how exactly does this happen? Does the crust form from one big magma pool, or from several pools at different depths? Now, some new images from the Juan de Fuca Ridge in the Northeast Pacific have helped clarify the story. By recording how seismic waves reflect off lower regions of the crust, researchers have discovered evidence supporting the idea that the crust is formed from multiple bodies of magma. They reported their findings in the journal Nature.

Map showing location of Juan de Fuca Ridge

» More: a press release about this research

 

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More recent discoveries about the creatures that live near hydrothermal vents.