Our Beautiful World

Submarine volcanoes and more
in the Mariana Arc

The 2004 Submarine Ring of Fire exploration by NOAA, was a follow-up to last year’s trip
along the Mariana Arc volcanic chain. The 2003 expedition surveyed more than 50 submarine
volcanoes and discovered that 10 of them had active hydrothermal systems.

Sea-floor hot springs are well known along the mid-ocean ridge system, because they were first
discovered more than 25 years ago. In comparison, the hydrothermal systems of submarine
volcanoes along island arcs are relatively unexplored, especially in terms of modern exploration
tools. Preliminary work at a few sea-floor sites and analyses of samples from last year indicate
that island arc hydrothermal systems are probably very different in character (e.g., morphology,
eruptive style, chemical composition) from those found along the mid-ocean ridge.
This expedition was one of the first comprehensive investigations of this type of submarine
volcanic environment.

Baker et al. 2008 identified 76 volcanic edifices along 1370 km of the Mariana arc, grouped into 60 ‘‘volcanic centers,’’
of which at least 26 (20 submarine) are hydrothermally or volcanically active. The overall volcanic center density is 4.4/100 km of arc,
and that of active centers is 1.9/100 km. Active volcanoes lie 80 to 230 km above the subducting Pacific plate

Rota I volcano

Giant smoky plume discovered pouring out of "Brimstone Pit" crater near the summit of NW Rota 1 volcano.
The first site found (above the pit) was a large area of sand with shimmering water percolating through it.
Inserting a temperature probe in it yielded a temperature of over 100 C!
A huge amount of heat and highly acidic fluid is coming out of this large area of sand.
Click here to see the map of the Mariana Arc

NW Rota. The volcano rises to a height of 535 meters below sea level. Its base is over 2000 meters deep.
Brimstone Pit is near the summit of the volcano at 555 meters depth.

While the pilots were trying to tend to a troublesome suction sampler at 560 meters (1840 feet),
a large burst from the Brimstone Pit (which clearly has two side-by-side eruptive vents)
almost engulfs the vehicle in an ash plume.
Video courtesy of Submarine Ring of Fire 2006 Exploration, NOAA Vents Program, NOAA-OE.
Uploaded by oceanexplorergov on Dec 11, 2006

This volcano is a Mt. Fuji-like cone rising about 2,500 m above the surrounding sea floor. In 2003, the expedition
found a 200-m-thick layer of intense hydrothermal plumes above the volcano summit. These plumes extended for at least
several kilometers around the summit, indicating that a vigorous hydrothermal vent system was active. The plumes were
organized into several distinct layers, suggesting that multiple vents were discharging fluids of differing temperatures.

Unusual spiny crab spotted on NW Rota 1 volcano. Crabs are opportunistic predators at vent sites.
The body of this crab is ~2 in. (~5 cm) across.
The unusual chemistry here indicates that at least some of the vents on NW Rota #1 are rich in sulfuric acid.
Sulfur is a rich energy source for the microbes that live in hydrothermal systems.
All other life in the hydrothermal ecosystems depend on these microbes.

Chemical analysis of the plumes showed that they were among the most unusual ever found above a hydrothermal source.
The particles suspended in the plumes contained the highest concentration of particulate aluminum ever recorded,
in addition to high concentrations of sulfur, iron, and manganese.

East Diamante volcano

Click here to see the map of the Mariana Arc

Active “smoker” chimneys precipitating iron, copper and zinc sulfides from 230ºC fluid.
They are 9 m tall from the base to the top of the chimneys. Dark beehive-type chimneys,
here about 30 cm tall, commonly sit on top of these structures.

After reaching the sea floor at East Diamante, low-temperature diffuse venting was quickly recognized amidst the
boulder-strewn slope. The presence of barnacles (possibly a new species) coined the name of the first site as
“Barnacle Beach." After a short search around the rim of the cone, the expedition came across a line of sulfide
chimneys (named the “Black Forest”) upslope of Barnacle Beach.

This may be a unique photograph of a shallow-water tropical fish swimming among active
black smoker chimneys at Black Forest vent field. The chimneys rise up to 7 m tall.

This stunning image of Aquarium site shows the picturesque gully with its abundant sea life,
which includes algae (red and green), soft corals (pink with white stalks) and tropical fishes.
(See the map above)

This is a small, ice-cream-cone-shaped chimney located near the base of Five Towers,
which shows the affects of hydrothermal fluid boiling on the sea floor.

There are at least 50 chimneys in the area named the “Black Forest." Most of the chimneys seen were dead;
that is, hot water had ceased to flow within them. Most were around 2 m tall but some stretched up to 9 m
off the sea floor. Moving upslope amongst the chimneys, the expedition discovered that some were very
much alive. One group, aptly named “Five Towers," had a large base several meters in diameter with individual
chimneys 7-9 m high that spewed black smoke into the surrounding seawater.

The expedition have never seen a field of chimneys like this in such shallow water. Finally, they witnessed a rarely
seen phenomenon. They saw evidence of hot water boiling right at the exit point of one of these chimneys,
where streams of bubbles (gas) emanated from one part of the chimney while hot liquid escaped from a different part.

On the summit of East Diamante (170 m, 558 ft depth), all signs of hydrothermal venting have disappeared.
Soft corals (~10-15 cm or 4-6 in tall) and tropical fish share the paradise named “Aquarium."

Maug volcano and Islets

Left: The vertical column in the center of the image, called a dike, rises from below sea level to the pinnacle at the top
of the ridge. Interlaid massive lavas (darker horizontal bands) and ash-rich lava units (reddish) are also exposed
on the islets of Maug
Right: Three-dimensional view of the Maug caldera, ranging in depth from 241 to 25 m
Click here to see the map of the Mariana Arc

An aerial view of the Maug Islands from the NE shows Kita-shima (North Island) at the right margin,
Higashi-shima (East Island) in the foreground, and Nishi-shima (West Island) in the background.
The islands enclose a 2.5-km-wide submarine caldera that contains a submerged lava dome that rises to within
about 20 m of the sea surface. No eruptions are known from the Maug Islands since their discovery by Espinosa in 1522.

Photo by Dick Moore, 1990 (U. S. Geological Survey).

The Maug Islets consists of three small elongated islands up to 2.3 km long mark the northern, western,
and eastern rims of a largely submerged 2.5-km-wide caldera. The highest point of the Maug Islands reach
only 227 m above sea level; the submerged southern notch on the caldera rim lies about 140 m below sea level.

Eifuku volcano

White chimneys at Champagne vent site, NW Eifuku volcano.
The chimneys are ~20 cm (8 in) across and ~50 cmhigh, venting fluids at 103ºC (217ºF).
Click here to see the map of the Mariana Arc

During the first dive at NW Eifuku volcano, a remarkable hydrothermal site was discovered near the summit,
1,650 meters (more than 1 mi) below sea level. Small white chimneys vented cloudy white fluid at the site.
Surprisingly, bubbles composed of some sort of fluid were rising out of the sediment around the chimneys.
Bubbles have been seen before in hydrothermal systems, but never in such great abundance.

Close-up of bubbles at the Champagne Vent.

It’s obvious why the site was named “Champagne”. The bubbles were slightly opaque, only barely buoyant,
and sticky, adhering to surfaces on the ROPOS ROV (the camera-robot). The bubbles also differed from typical gas
bubbles in that they had little tendency to fuse into larger bubbles, even when touching each other.

These fluids want to expand over 50 times in volume as the ROV ascends to the surface, because the confining
weight of seawater pressure is removed.

A tremendous mussel biomass adorned the lava ridges at the crest of NW Eifuku volcano.
They were attached by sticky threads (known as byssal threads) spun by each animal's foot.
Other than being much larger -- these deep-sea mussels were up to 18 cm (7 in) long -
- they were very similar to their intertidal cousins.

At NW Eifuku volcano, mussels are so dense in some places that they obscure the bottom.
The mussels are ~18 cm (7 in) long. The white galatheid crabs are ~6 cm (2.5 in) long.

Mussels are found at hydrothermal vents and cold seeps around the world. They are part of the genus Bathymodiolus,
first discovered at hot vents off western Mexico. While their presence here was not a big surprise, their density
and the relative lack of other fauna were intriguing. Unlike elsewhere, these mussels were not residing in cracks
or clustered around flowing vent water. Instead, they were clustered on the tops of rocks. The Champagne smokers were located downslope from the mussels,
but there was no temperature anomaly in the water around the mussels.

This report is based on the "Submarine Ring of Fire 2004: Mariana Arc Expedition "
National Oceanic and Atmospheric Administration | U.S. Department of Commerce


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