Introduction
All over the Earth, underneath the oceans,
volcanoes are erupting.
Arrayed in mountainous chains called spreading centers, each volcano is a natural
expression on the seafloor of the convective cooling of the planet's interior. Magma
heated (to some 1300 oC) in the Earth's mantle by radioactive decay erupts at the
divergent plate boundaries, cools, and solidifies to form the oceanic
crust. The cold (about 2 oC) ocean bottom water transports the heat from the rock,
either through convection or conduction. As the crust cools, the ocean warms,
and ultimately -- through circulatory and radiative processes in the sea and atmosphere
-- heat moves from inside the Earth to space. Through this physical process and
persuant biogeochemical phenomena, submarine volcanoes can
change the properties of the oceans; in particular, they have an observable
effect on deep-sea hydrography.Just as volcanic eruptions on land affect the atmosphere (with plumes of steam, ash clouds, fumaroles, and pyroclastic flows), submarine volcanoes affect the oceans with a variety of observed phenomena: event plumes; baroclinic vortices; "black smoker" venting through mineral chimneys (see image); underflow from overhanging sulfides; percolation through sediments, talus, or biological (tube worm or clam) beds; and conduction from warm basalt. The activities are diverse, but all are driven by the behavior of water when its density is changed in a gravitational field.
The density of liquid water changes in some fantastic fashions in response to heat, solute concentrations, and pressure, in accordance with the equation of state. While density increases slightly from the freezing temperature, it decreases upon further warming. Consequently, if a parcel of deep-ocean water (>~1.5oC)is light relative to the surrounding water, it will rise. Such buoyant behavior, balanced with the viscous characteristics of water, results in a bevy of fluid flows, some of which are explored in this report.
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If you have comments or suggestions, email me at scottv@ocean.washington.edu
This research was conducted within the
University
of Washington Geophysical Fluid Dynamics Laboratory