| A | B |
|---|
| magma | liquid rock formed under Earth’s surface, by excess pressure and/or temperature |
| volcanism | any activity that includes the movement of magma toward or onto Earth’s surface |
| lava | magma that flows onto Earth’s surface |
| volcano | a vent or fissure in Earth’s surface through which magma and gases are expelled |
| The Ring of Fire | A major zone of active volcanoes which encircles the Pacific Ocean |
| hot spot | a weak area of Earth’s surface, usually in the middle of a plate, that produces magma to form island chains as the lithosphere (plate) moves |
| plutons | large formations of igneous rock that did not reach the Earth’s surface |
| dikes | small plutons |
| batholiths | large plutons, like the Sierra Nevadas |
| viscosity | the thickness of the magma |
| pyroclastic material | fragments of rock that form during a volcanic eruption |
| mafic | magma that is rich in magnesium and iron and that is dark in color. Eg. ocean crust and Hawaiian volcanoes. |
| felsic | magma that is rich in feldspar and silica and that is light in color. Eg. continental crust, Mount St. Helens. |
| shield | a type of volcano with a broad base from mafic lava |
| cinder cone | smallest, most common type of volcano made of cinder pyroclastic rock. Eg. Red Hill, Owens Valley |
| composite or strato | a type of volcano with steep slopes from felsic lava. Eg. Japan’s Mt Fuji, Italy’s Mt Vesuvius. |
| caldera | a large, circular depression or valley that forms when the magma chamber collapses. Eg. Long Valley Caldera, near Mammoth CA. |
| warning signals of volcanoes | escaping gas and earthquakes |
| earthquake | a movement of the ground that is caused by a release of energy when rocks along a fault suddenly move |
| fault | a break in a body of rock along which one block moves relative to another |
| focus | the location within Earth along a fault at which the first motion of an earthquake occurs |
| epicenter | the point on Earth’s surface above the focus |
| P wave | a primary wave, or compression wave |
| S wave | a secondary wave, or shear wave S waves are the second-fastest seismic waves and can only travel through solids |
| surface waves | formed when P waves or S waves reach Earth’s surface |
| shadow zone | an area on Earth’s surface where no seismic waves from a particular earthquake can be detected\ |
| seismology | The study of earthquakes and seismic waves |
| seismograph | an instrument that records vibrations in the ground |
| seismogram | a tracing of earthquake motion that is recorded by a seismograph |
| magnitude | a measure of the strength (amount of ground motion) of an earthquake |
| intensity | the amount of damage caused by an earthquake |
