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Did
you know that the Earth's longest mountain range is
underwater?
The
Mid-Ocean Ridge system, snaking its way between the continents,
is more than 56,000 kilometers long. This series of mountains
and valleys marks the areas where the Earth's crustal
plates are moving apart. This is where most hydrothermal
vents are located. The University of Delaware's Extreme
2002 deep-sea dive site is in an active vent field in
the Pacific Ocean more than 1,000 miles west of Costa
Rica.
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Earth's
Moving Crust Spawns Vents, Volcanoes & Quakes
 Understanding
where hydrothermal vents occur requires a closer look at the Earth's
structure and the forces at work deep within the planet.
The deeper you go inside the Earth, the hotter it gets. Scientists
have calculated that the Earth's inner core — a solid sphere
composed primarily of iron — is about 5,500° C (10,000°F).
That's about the same temperature as the surface of the sun. The
solid inner core is about 2,400 kilometers (1,500 mi) in diameter.
It is surrounded by a liquid outer core about 2,225 kilometers
(1,380 mi) thick.
Bordering the liquid outer core is the mantle, which is composed
of hot, molten rock called magma. The churning of the magma generates
pressure on the Earth's surface layer, or crust. The crust is very
thin and brittle compared to the other layers. It ranges in thickness
from only about 3 kilometers (2 mi) in some areas of the ocean
floor to some 120 kilometers (75 mi) deep under mountains on the
continents.
According to the theory of plate tectonics, the Earth's crust
is made up of about a dozen plates on which the continents and
the oceans rest. These plates are continually shifting because
the surface beneath them — the hot, magma-filled mantle — is
moving slowly like a conveyor belt, driven by the heat in the Earth's
core. The plates currently move about a centimeter (0.5 in) to
15 centimeters (6 in) per year in different directions.
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This
map shows the major tectonic plates that make up the
Earth’s crust and the directions in which they are moving.
Map adapted from NOAA.
 Click
Here to reveal the tectonic plates that surround
our expedition site.
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 The
Earth's tectonic plates can move apart, collide, or slide past
each other. The Mid-Ocean Ridge system — the Earth's underwater
mountain range — marks where the plates are moving apart.
As the plates part, the seafloor cracks. Cold seawater seeps deep
down into these cracks, becomes super-heated by magma, and then
gushes back out into the ocean, forming hydrothermal vents.
As the plates move farther apart, magma from the Earth's interior
percolates up to fill the gap, sometimes causing earthquakes and
the eruption of undersea volcanoes. This process, called seafloor
spreading, is how new seafloor is formed.
The Earth's size is constant, so as the crust expands through
seafloor spreading in one area, crust must be swallowed up elsewhere.
Crust is destroyed when the edge of one tectonic plate is forced
underneath another. This dynamic process is called subduction. It
results in earthquakes, volcanoes, and the formation of deep ocean
trenches.
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