TECTONIC PLATES A large part of the earth's crust that moves as a unit 

 with respect to other plates. 



TEPHRA Clastic material that has been ejected from a volcano. 



TERRESTRIAL Pertaining to land as opposed to the ocean. 



TILT Sideways inclination of an aircraft or spaceship. 



TSUNAMI A long-period wave caused by an underwater disturbance such as 

 an earthquake. Tsunamis are often highly destructive if they reach a coast. 



TIDAL PRISM The total amount of water that flows into a lagoon, harbor, 

 or estuary and out again with the rise and fall of the tide. 



WAVE STEEPNESS The ratio of wave height to wave length. 



WEATHERED The condition of rocks that have undergone physical and/or 

 chemical alterations due to exposure to the elements. 



YAW Refers to an aircraft's or spaceship's turning by angular motion about 

 a vertical axis. 



Appendix A Glossary of Geologic Terms 



A7 



