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TITLE: The Inner Earth


[Photo: Volcano Cross-section]

Despite striking variations in size, shape, and behavior, all of Earth’s volcanoes share one trait: They grow by ejecting lava or hot rock fragments that accumulate around their vents. Over tens to millions of years, the products of repeated eruptions construct an edifice.

Magma, Lava or Tephra?

Magma is molten rock below ground. It consists of liquid, suspended crystals, and gases.

Lava is magma that erupts non-explosively. Rocks formed when the flowing liquid solidifies are also called lava.

Tephra include all sorts of fragments formed when magma erupts explosively large bombs, small cinders, pumice, and ash.





1. Pyroclastic flow:
Swirling cloud of pumice, ash, and hot gas.

2. Old tephra:
Debris from earlier explosive eruptions.

3. Summit crater:
Depression at the site of summit eruptions.

4. New tephra:
Debris from recent explosive eruptions.

5. Central conduit:
Passage through which magma is erupted.

6. Flank vents:
Sites of eruptions on the flanks of the volcano.

7. Young lava flows:
Lavas from recent eruptions exposed on the surface.

  [Photo: Volcano Cross-section]

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits