| A | B |
|---|
| tremor | a slight shaking of the Earth's crust |
| seismograph | an instrument that measures the Earth's crust |
| earthquake | sudden, strong movements in the earth's crust |
| fault | a break in the crust of the earth |
| focus | the place within the crust of the earth where an earthquake starts |
| epicenter | the place on the surface of the earth directly above the focus |
| seismologists | scientists who study earthquakes |
| seismogram | sheet of paper showing the wavy lines drawn by a seismograph |
| Richter Scale | scale that measures how long an earthquake is |
| volcanism | movement of molten rock on or inside the earth's crust |
| domed mountain | a mountain formed by magma pushing up through the crust to form a dome shape |
| dike | magma that cuts across layers of rock in the earth's crust |
| fissure | a crack in the earth's crust |
| cinders | solid pieces of lava that are thrown out of a volcano |
| volcano | an opening in the earth's crust from which lava comes out |
| crater | a hole at the top of a volcano |
| volcanic cone | a mountain built up around the opening of a volcano |
| explosive volcano | a volcano that shoots up through the surface with great force |
| quiet volcano | a volcano formed when lava flows freely through the surface |
| mountain | mound of land whose elevation is at least 600 meters higher than the surrounding land |
| anticline | upward fold of rock layers |
| syncline | downward fold of rock layers |
| plain | large, flat area whose elevation differs little from that of the surrounding area |
| plateau | large, flat area whose elevation on at least one side is sharply higher than that of the surrounding area |
| fault plateau | a plateau formed when land on one side of a fault is raised up |
| continents | very large areas of land |
| theory of continental drift | a theory that states that continents have been moving and still are moving |
| tropics | region near the equator where it is hot and damp |
| theory of plate tectonics | a theory that states that the earth's crust is cracked to form about 20 large pieces |
| crustal plates | the large pieces of the earth's crust |
| convection current | the movement of material within a fluid caused by uneven temperature |
| convection cell | a convection current that flows around in a loop |
| Mid-Atlantic Ridge | a large underwater mountain range running down the middle of the Atlantic Ocean |
| ocean floor spreading | the widening of the ocean |
| ocean trench | a deep ditch in the ocean |
