| A | B |
|---|
| earthquake | The shaking and movement of the Earth's crust |
| Mexico City | A powerful earthquake in 1985, many people died. |
| Mount Saint Helens | In 1980 it erupted, the Earth rumbled for daysbefore and after. |
| moving crust | Evidence can be found in the Earth. Sometimes layers are across others, tilted a bit and folded. |
| fossils | Fossils give clues about crust movement. It also shows animals from the ocean on mountains. |
| crust | Continental crust is made of granite . Oceanic crust is made of basalt. |
| mantle | Most earthquskes and volcanoes happen in the crust and first and srcond layer of the mantle. |
| compression | The pressure that occurs when two forces push against rock layers from opposite sides. |
| tension | A force that pulls the rocks in the Earth's crust apart. |
| fault | A crackof fracture in rock along which the rock on either side of the fault may move. |
| shearing | A force that causes a large block of rock to slide past another block of rock. |
| dormant volcano | A volcano that has not shown any activity for a long period of time. |
| extinct volcano | A volcano that has not erupted for thousandsof years. |
| Pangaea | The name given to a giant landmass that exited when all the continents were together. |
| focus | The place inside the Earth where an earthquake begins. |
| seismic wave | A vibration in the Earth beginning at the focus of an earthquake. |
| epicentre | The place on the surface of the Earth, directly above the focus, where an earthquake is first felt. |
| seismograph | An instument used to record seismic waves.` |
| L waves | Seismic waves that move along the surface of the Earth. |
| P waves | Seismic waves that cause rocks in the Earth to vibrateback and forth. |
| S waves | Seismic waves that cause rocks in the Earth to vibrate up and down. |
| Seismologist | A scientist who studies earthquakes. |
| Richter scale | A scale used to determine the magnitude of an earthquake. |
| Cinder cone | Akind of structure formed when a vocano erupts violently. |
| Shield cone | A knid of structure formed when lava flows periodically from a volcano's vent. |
| Composite cone | A kind of structure formed by vocanoes that alternate between being quiet and being violent. |
| Plate | Part of the Earth made up of the crust and the first layer of the mantle. |
| Plate Tectonics | A theory that explains how plates of the Earth move. |
