Across
- 4. The thin outer layer of the Earth's surface, averaging about 10 kilometers thick under the oceans and up to about 50 kms thick on the continents. This is the only layer of the Earth that humans have actually seen.
- 5. A steep-sided mount that forms when very viscous lava is extruded from a volcanic vent.
- 6. The term used for magma once it has erupted onto the Earth's surface.
- 7. The opening at the Earth's surface through which volcanic materials (lava, tephra, and gases) erupt. Vents can be at a volcano's summit or on its slopes; they can be circular (craters) or linear (fissures).
- 11. The circular depression containing a volcanic vent.
- 12. The innermost layers of the Earth. It is solid and has a radius of about 1300 kms. (The radius of the Earth is about 6371 kms.) The outer core is fluid and is about 2300 kilometers thick. S-waves cannot travel through the outer core.
- 14. The process in which one lithospheric plate collides with and is forced down under another plate and drawn back into the Earth's mantle.
- 17. (Plate) The theory that the Earth's crust and upper mantle (the lithosphere) is broken into a number of more or less rigid, but constantly moving, segments or plates.
- 18. A vent (opening) in the surface of the Earth through which magma erupts; it is also the landform that is constructed by the erupted material.
- 20. Shaking of the Earth caused by a sudden movement of rock beneath its surface.
- 21. A volcano that has erupted in the past, still active and is expected to erupt in the future.
- 23. One of the huge sections which make up the Earth's crust. The plates are continuously moving.
Down
- 1. (Plate) The place where two or more plates in the Earth's crust meet.
- 2. The layer of rock that lies between the crust and the outer core of the Earth. It is approximately 2900 kms thick and is the largest of the Earth's major layers.
- 3. A weak point in the Earth's crust and upper mantle where the rock layers have ruptured and slipped. Faults are caused by earthquakes, and earthquakes are likely to reoccur on pre-existing faults.
- 8. (Volcano) A volcano that is not expected to erupt again.
- 9. A risk. An object or situation that has the possibility of injury or damage.
- 10. That point on the Earth's surface directly above the hypocentre of an earthquake.
- 13. (Drift) The theory, first advanced by Alfred Wegener, that they were originally one land mass. Pieces of the land mass split off and migrated to form the continents.
- 15. (Volcano) A volcano that resembles an inverted warrior's shield. It has long gentle slopes produced by multiple eruptions of fluid lava flows.
- 16. (Subduction) An elongated region along which a plate descends relative to another plate, for example, the descent of the Nazca plate beneath the South American plate along the Peru-Chile Trench.
- 19. A steep-sided volcano formed by the explosive eruption of cinders that form around a vent.
- 22. Molten rock containing liquids, crystals, and dissolved gases that forms within the upper part of the Earth's mantle and crust. When erupted onto the Earth's surface, it is called lava.