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Ch.10 Volcanoes
| Question | Answer |
|---|---|
| What are the primary factors that determine whether a volcano erupts violently or quietly? | They include magma composition, magma temperature, and the amount of dissolved gases in magma. |
| A substance's resistance to flow is its _________ | Viscosity |
| How does temperature affect viscosity? | If lava flow is heated its mobility increases and its viscosity decreases. When lava flow starts to cool it's viscosity increases. |
| How does silica content affect viscosity? | In general, the more silica in magma, the more viscous it is. Because of their high silica content rhyolitic lavas are more viscous whereas basaltic lavas, low in silica, are more fluid. |
| An opening to the surface is a _____________. | vent |
| Eruptions of fluid basaltic lavas are a) relatively quiet b)explosive and loud | a) relatively quiet |
| The gases ejected from a vent are mostly _________ and _____________. | water vapor and carbon dioxide. |
| When fluid basaltic lavas harden, they commonly form a relatively smooth skin the wrinkles as the still-molten subsurface lava continues to move. These are known as ____________flows and resemble the twisted braids in ropes. | pahoehoe |
| Another common type of basaltic lava is called _______ and has a surface of rough jagged blocks with dangerously sharp edges and spiny projections. | aa (pronounced AH ah) |
| The gaseous portion of most magmas is only about how much? | 1 to 6 percent. |
| Why is the composition of volcanic gases important? | They have contributed greatly to the gases in the atmosphere. |
| _________________________ is the name given to particles produced in volcanic eruptions. | Pyroclastic Material |
| Particles that range in size from small beasds to walnuts are called _________ | lapilli |
| Particles larger than 64 milimeters in diameter are called ________ when they are made of hardened lava and __________ when they are ejected as glowing lava. | blocks, bombs |
| Because bombs are semimolten, they take on a ______________ shape as they hurl through. | streamlined |
| Repeated eruptions of lava or pyroclastic materials often seperated by longs inactive periods eventually build the mountain called a ________________ | volcano |
| Located at the summit of many volcanoes is a steep-walled depression called a _______ | crater |
| ___________________ are produced by the accumulation of fluid basaltic magmas. They are broad, domed structures. | Shield volcanoes |
| Ejected lava fragments the size of cinders which harden in the air form a ____________ | cinder cone |
| A _______________________ is a large, nearly symmetrical structure composed of layers of both lava and pyroclastic deposits. | composite cone |
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