Geothermal Energy

What is the origin of the heat energy erupting from Earth's surface?

Earth formed by accretion from solar nebula — an interstellar cloud of dust, hydrogen, helium and other ionized gases — about 4,540,000,000 years ago.

Extreme volcanism and collisions with other bodies made much of the nascent planet's surface molten. Volcanic gases formed a fledgling atmosphere.

Bárðarbunga Volcano, 4 September 2014

Image: Peter Hartree

As the planet cooled, it formed a solid crust. Rocks in the core and mantle remain hot from the original materials colliding at high speeds.

Terminology:
Magma refers to molten rock still underground. If molten rock erupts onto the surface, it is called lava. Lava is liquified rock at 1,292 to 2,192 °F (700 to 1,200 °C).

Bárðarbunga Volcano, 2 September 2014

Image: Arctic-Images/Corbis

Collision energy is the source of heat trapped below Earth's crust. Heat below Earth's crust is called geothermal energy.

May not subterraneous fire be considered as the great plough which Nature makes use of to turn up the bowels of the earth?
— Sir William Hamilton

REFERENCES

• 11 Photos of Iceland's Bardarbunga Volcano Erupting That Are Just Unreal, Mashable, 12 Sep 2014.
• Bárðarbunga, Wikipedia.
• How is lava formed, Oregon State University Volcano World.

Tectonic Fire

Observing Mount Vesuvius, Mount Etna, and other Volcanoes, Sir William Hamilton posited

May not subterraneous fire be considered as the great plough (if I may be allowed the expression) which Nature makes use of to turn up the bowels of the earth? — Sir William Hamilton, 1774

Steam plume rising from Shishaldin.
28 January 2014.

A steam plume and elevated surface temperature were recently observed at Mount Shishaldin. The Shishaldin volcano is located on Unimak Island in the Aleutian Islands.

Mount Shishaldin is the highest peak in the Aleutian Islands. Shishaldin is distinguished as the most symmetrical cone-shaped glacier-clad mountain on earth.

Native Aleuts called the volcano Sisquk meaning:

Mountain which points the way when I am lost.

Unimak Island, and its highest peak, rise above one of the most active plate boundary zones on earth. The collision of the Pacific oceanic plate and the North American continental plate cause frequent earthquakes and volcanic activity.

Subduction of Pacific oceanic plate along the Aleutian Trench.

The oceanic plate is heavier than the continental plate, so it is forced below the edge of the continental plate. The ongoing process, called subduction, generates extreme stresses and heat.

And many a fire there burns beneath the ground.
— Empedocles, 490 BC.

The Aleutian Trench

The subducting oceanic plate is marked by the Aleutian Trench which runs along the Aleutian Islands and the Alaska Peninsula. The Aleutian Trench is 22,638 feet deep south of Unimak Island.

Shishaldin and Isanotski Volcanoes, Unimak Island, Aleutian Islands

REFERENCES

• Alaska Volcano Observatory.
• Eastern Aleutian Volcanic Arc Digital Model - Version 1.0, USGS.
• Global Volcanism Program, Smithsonian Institution.