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Deepseawaters
Home Hydrothermal
Vents
Hydrothermal Vents
History
 For
over 20 years, the PMEL Vents Program has
investigated the effects on the oceans of deep-sea
volcanoes and hydrothermal systems.
The approach of the Vents Program has combined exploration,
long-term time series observations, remote monitoring, and
innovative oceanographic instrumentation with an aim of providing
timely information to the scientific community and the general
public via peer-reviewed scientific publications and internet-accessible
data and educational products.
Over
70% of the earth's volcanic activity takes place beneath the
sea surface, where it has an impact on deep
ocean mixing, the global chemical and heat balance,
and what may be the most ancient biological communities on
the planet. PMEL/Vents is recognized for conducting unique
research on submarine hydrothermal systems that address these
key issues. By gaining access to data from the Navy's "SOSUS"
acoustic monitoring system and developing additional hydrophone
systems at PMEL, Vents has been locating earthquakes
and using natural ambient ocean sound to study whales and
alert scientists about ongoing volcanic eruptions on the seafloor.
This acoustic monitoring led to the first remote detection
and response to a seafloor volcanic eruption in 1993 on the
Juan de Fuca Ridge in the NE Pacific. Since that time, PMEL
has detected several more volcanic eruptions on the Juan de
Fuca and joined academic researchers from the university community
in rapid response efforts to identify the immediate effects
of volcanic activity.
Concepts of Hydrothermal
Vents
 Hot
springs on the ocean floor are called hydrothermal
vents. The most numerous and spectacular hydrothermal
vents are found along world's mid-ocean ridges. The heat source
for these springs is the magma (molten rock) beneath the volcanic
ridge system. Geothermal activity beneath 2000 to 5000 meters
of seawater is markedly different than on
land because of the high pressure at the bottom of the ocean.
As seawater descends into the region of partly molten rock
beneath the mid-ocean ridge, it heats up to 300-400°C and
becomes extremely corrosive. This hot fluid is capable of
dissolving the surrounding basaltic rock and leaching out
metals and other elements. This 300-400°C fluid is also very
buoyant and begins rising rapidly back to the surface, and
eventually reenters the ocean at hydrothermal vents.
 The
most spectacular kind of hydrothermal vent are called "black
smokers", where a steady stream of "smoke"
gushes from a chimney-like structures. The "smoke" consists
of tiny metallic sulfide particles that precipitate out of
the hot vent fluid as it mixes with the cold seawater. Plumes
from such vents can be traced in the ocean for hundreds of
meters upwards and hundreds of kilometers horizontally. The
chimneys are made out of sulfide minerals that precipitate
out of the vent fluid and can grow 10's of meters high. Many
large ore deposits now found on land were formed at hydrothermal
vents millions or even billions of years ago. Black smokers
are an example of focused vents, in which almost all the vent
fluid comes out of one small pipe.
Sometimes
the hot fluids rising from depth are mixed with cold seawater
and spread out before they emerge back onto the seafloor.
These are called diffuse vents and are usually only a few
tens of degrees above the near freezing deep ocean
water. Diffuse vent areas have warm water exiting
the seafloor over a large area and consequently
do not build sulfide chimneys. However, they still contain
high levels of hydrogen sulfide and other compounds that specialized
microbes can use for energy. This is the basis for an ecosystem
that is largely independent of the sun and gives rise to the
specialized vent animals such as large tubeworms and clams.
The relatively low temperature allows the animals to remain
immersed in the nutrient rich water and allows the diffuse
vent sites to develop into complex ecosystems. Often chimneys
with focused, high-temperature venting are surrounded by areas
of diffuse, low-temperature venting.
PMEL/Vents Program
The
Vents Program has developed and deployed innovative instruments
to monitor and quantify volcanic and hydrothermal processes.
A large effort has been focused on the New Millennium
Observatory (NeMO) at Axial Volcano on the Juan de
Fuca Ridge, where a suite of instruments has been monitoring
volcanic and hydrothermal activity nearly continuously for
over six years. One of the goals of NeMO is to understand
the extent of the sub-seafloor biosphere and to link the geologic,
chemical, and biological processes that have allowed life
to thrive in and around submarine volcanoes for billions of
years. Recent studies using a unique sampling tool (the Hydrothermal
Fluid and Particle Sampler) have shown how microbial communities
respond to changing conditions following a volcanic eruption.
NeMO includes many temperature sensors in hot springs, deep-ocean
moorings with physical sensors, continuous geodetic measurements,
inter-annual sampling and survey missions, an exciting education
and outreach component, and a unique, real-time, two-way communication
system (NeMO-Net). NeMO-Net provided images of hydrothermal
vents in the first two years, and now has geodetic and chemical
sampling capability. A bottom pressure recorder monitors volcanic
inflation/deflation associated with magmatic activity, and
the interactive sampler monitors vent temperature and pH and
collects samples on a weekly schedule or on command. Using
underwater acoustic and satellite data transmission, NeMO-Net
is the first deep-ocean observatory with the capability to
respond from shore to a volcanic or hydrothermal event. This
pioneering technology to connect deep-sea observatories in
remote locations to shore-based laboratories will be a major
part of the global scale Ocean Observatories Initiative.
The
Vents Program has become increasingly global in scope to reflect
the nature of seafloor volcanism and to explore the full range
of processes that occur in the wide range of volcanic environments
beneath the sea surface. Autonomous acoustic
monitoring now covers significant parts of the Pacific and
Atlantic oceans. Vents Program scientists
have led expeditions to explore venting on the remote, super-fast-spreading
East Pacific Rise from 11 to 32°S, on the Explorer ridge
in the NE Pacific, and on the Mariana volcanic arc in the
western Pacific. With a coordinated team of geophysicists,
geologists, oceanographers, chemists, and collaborating biologists
and microbiologists, the Vents Program is poised to make new
discoveries about the tectonic and volcanic processes that
shape our planet.
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