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Volcanoes!!!!
| Question | Answer |
|---|---|
| What are the three factors that determine the violence of an eruption? | 1. Composition of the magma 2. Temperature of the magma 3. Dissolved gases in the magma |
| Viscosity | A measure of a material's resistance to flow |
| What are the three factors that affect viscosity? | 1. Composition( silica content) 2. Temperature( hotter magmas are less viscous) 3. Dissolved gases( volatiles) Mainly water vapor and carbon dioxide. Gases expand near the surface |
| What does it mean the there is a high silica content in the magma? Low? | High silica means that there will be a high viscosity. A low silica means that there will be a more fluid like magma |
| What are volatiles composed of mainly? | Water vapor and carbon dioxide |
| What is the function of dissolved gases ( volatiles)? | Provide force to extrude the lava. |
| What are the things that make up a more violent eruption? | 1. How easily the disssolved gases can escape from the magma 2. If the magma is viscous. |
| What are the two types of lava flow? | 1. Pahoehoe 2. Aa |
| What does the pahoehoe lava flow resemble? | It resembles a braid in ropes. |
| What does the Aa lava flow resemble? | Rough, jagged rocks |
| What are the two types of volcanic material? | 1.Lava flow 2.Pyroclastic material |
| What are some of the pyroclastic material? | 1. Ash and dust 2. Pumice |
| How can the ash and dust be described as? | Fine, glassy fragments |
| What is pumice from? | From " frothy" lava |
| What are the general features of a volcano? | 1. Conduit 2. Vent 3. Crater 4. Caldera |
| What is a conduit? | Conduit is a pipe that carries gas rich magma to the surface |
| What is a vent? | The surface opening( connected to the magma chamber via a pipe. |
| what is a crater? | Steep- walled depression at the summit |
| What is a caldera? | A summit depression greater than 1 km diameter |
| What are the three types of volcanoes? | 1. Shield 2. Composite cone 3. Cinder cone |
| What is a shield volcano? | It is a broad, slightly domed volcano that is primarily made of basaltic (fluid) lava. Generally large in size. Mauna loa in Hawaii is an example. |
| What is a composite cone (stratavolcano) ? | Large in size, inter-bedded lavas and pyroclastics. Most violent type of activity. Mt. St. Helens is an example |
| What does composite cones usually produce? | Nuee Ardente |
| What is a Nuee Ardente? | Fiery pyroclastic flow made of hot gases infused with ash. Flows down the sides of volcanoes at speeds of 125 mph |
| What can Nuee Ardente produce? | can produce a lahar , which is a volcanic mudflow. |
| What is a cinder cone? | Built from ejected lava fragments it has a steep slope, smaller in size than the other volcanoes, and frequently occurs in groups. Example sunset crater |
| What is a fissure? | Fluid basaltic lava extruded from crustal features |
| What is a pluton? | An underground igneous body. |
| How is a pluton classified? | By its shape ( which is tabular, sheetlike and massive) and orientation( with respect to the host ( surroundings) rock. |
| What is a discordant? | A type of pluton that cuts across existing structures |
| What is a concordant? | A type of pluton that cuts across parallel to features such as sedimentary strata. |
| What are the 4 types of igneous intrusive features? | 1. Dike 2. Sill 3. Laccolith 4. Batholith |
| What is a dike? | A tabular, discordant pluton |
| What is a sill? | A tabular, concordant pluton |
| What is a laccolith? | A lens shaped mass ( similar to a sill) concordant, arches overlying strata upward |
| What is a batholith? | Largest intrusive body, frequently from the cores of mountains |
| What is the origin of magma? | Originates when essentially solid rock, located in the crust and upper mantle, melts. |
| What are the 4 factors that influence the generation of magma from rock? | 1. Heat 2. Pressure 3. Volatiles 4. Partial melting |
| How does heat influence the generation of agma | Geothermal gradient is not suffiecent enough to melt all rock. Additional heat is generated by friction in the subduction zones, crustal rocks being heated during subduction, and the rising, hot mantle rocks(plumes) |
| How does pressure influence the generation of magma? | Increase in confing pressure causes an increase in melting temperautre. Drop in confining pressure can cause decompression melting this can lower the melting temperature and this occurs when a rock ascends. |
| How does volatiles influence the generation of magma? | It is made up of water, primarily. It causes the rock to to melt at a lower temperature. Plays a role in subducting ocean plates. |
| How does partial melting influence the generation of magma? | Igneuos rocks are mixtures of minerals. Melting occurs over a range of temperatures. Produces a magma with a higher silica content than the original rock. |
| Where are volcanoes most likely to occur? | Are located on the margins of the ocean basins( intermediate, andestitic composition). Second group is confined to the deep ocean basins ( basaltic lavas)Third group includes those found in the interiors of continents. |
| Are volcanoes located at the convergent plate boundaries? | This is where deep ocean trenches are generated . these descending plates are partially melted and the magma slowly rises. |
| What can rising magma(convergent plate boundaries) form? | Volcanic island arc in an ocean and the continental volcano arcs. |
| Are volcanoes loacted at the divergent plate boundaries? | When the lithosphere pulls apart large quantities of fluid basaltic magma are produced. |
| Along what type plate boundary are volcanoes most likely to occur? | Divergent |
| What is intraplate igneous activity? | Activity within the rigid plate where plumes of hot mantle rises ( hot spots) Hawaiin islands are an example. |
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