earth science ch. 10
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69 terms
Terms | Definitions |
|---|---|
 Volcano | an opening in the earth's crust through which molten lava and/ or gasses erupt |
| Plate boundaries | places where the Earth's crust is fractured apart into seperate plates |
| Ocean spreading center | in the middle of the ocean, underwater where plates are splitting apart |
| an example of an ocean spreading center is | mid-atlantic ridge |
| rift valleys | On a continent where plates are splitting apart |
| ex of rift valley | east african rift valley |
| continental margins | subduction zones |
| ex. of continental margins | western coast of S. america pacific northwest cascade mountains japan |
| hot spots | isolated areas with a magma plume, located in the middle of a tectonic plate |
| ex. of hot spots | hawaii and yellowstone |
| Volcanos can be different because of | variations in the magma |
| each magma has different____,______, and ______ | minerals, gasses, and viscosity |
| viscosity | a liquid's resistance to flow |
| low viscosity | fluid |
| high viscosity | very thick |
| what affects viscosity? | temperature and silica content |
| When the temp. of magma is higher | it flows faster |
| when there is more silica in magma | the thicker the lava |
| Gases can make an eruption very | explosive |
| Basaltic magma composition | is iron-rich, and low in silica and gasses |
| Basaltic is explosivity is | rare |
| Basaltic magma produces | Shield volcanos |
| Shield volcanos | they are low and broad and cover large areas |
| An ex. of a shield volcano | hawaii |
| Basalt magma with a higher gas content makes | cinder cones |
| cinder cone | small steep-sided volcanoes where exploding debris cools mid-air, and builds the sides of the volcanos |
| cinder cone usually erupt | once |
| Andesitic magma | includes 60% silica and 3-4% gases |
| Andesitic magma produces | composite cones |
| composite cones | large steep-sided volcano with sides made of layer of lava and erupts debris |
| Composite cones aka | strato volcano |
| composite cones erupt | multiple times |
| composite cones are very ______ and _________ | explosive and dangerous |
| many composite cones are located | on the ring of fire |
| ex. of composite cones are | mt. fuji, mt. rainer, mt st. helens |
| pluton | unit of rock where the magma never erupts but cools underground |
| batholith | massive rock unit (at least 100 mi2) that cooled underground |
| Many plutons come together to create a | batholith |
| Intrusive rock texture is | course- grained |
| granite is an example of | intrusive rock |
| Extrusive rock cools | the fastest |
| pumice | light coolered air pockets |
| scoria | darker color, air pockets |
| obsidian | volcanic glass |
| pumice, scoria, and obsidian are made of | adesitic and rhyditic lava |
| Basalt forms at | shield volcanoes, mid- ocean ridges and cinder cones |
| A lava flow can cool to form | aa or pahoehoe |
| aa | blocky and sharp |
| pahoehoe | ropey texture |
| Caldera | a depression in a volcanic mountain, caused by collapse into the empty magma chamber after eruption |
| how does a caldera form? 1 2 3 4 5 | 1. eruption occurs with many vents and cracks in the area 2. 3. eruption continues 4. volcano collapses into empty magma chambers 5. crater may become a lake |
| Lava flows | hot lava flows down a volcanoes side |
| tephra | fragmented broken material ejected from a volcano its usually airborne then falls around the crater |
| ash | it must be smaller the 2mm in diameter |
| lahar | a mixture of water and debris that results from a volcanic eruption |
| lahar forms when 1. 2. 3. 4. | 1. heat forms an eruption melts snow or ice on volcano 2. water rushes downhill with great velocity 3. the flood can pick up debris, dirt, ash, boulders, cars, etc. 4. begins with low viscosity ends with high viscosity ( cement like) |
| Pyroclastic flow | a cloud of hot, toxic gas that rushes downhill from a volcano extremly hot 100-800 degrees celcius |
| hot spots are | constant upwellings of magma in the same place. the plates of the lithosphere move over hot spots over long periods of time |
| Kauai | 4,000,000 |
| Oahu | 3,000,000 |
| maui | 1,000,000 |
| kohala | 100,000 |
| kilauea | currently errupting |
| the hawaiian hotspots have been active for at least | 100 million years |
| there is evidence there are hawaiian islands in parts of | the pacific |
| seamount | a mountain that rises from the sea floor, but does not break the surface of the water |
| why are seamounts no longer islands | it was probably once but probs got eroded away the top |
| The emperor seamount extends | to the northwest of hawaii |
| Mt. St. Helens is in | the cascades |
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