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| molten rock containing liquids, crystals, and dissolved gases that form within the upper part of the Earth's mantle and crust |
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| the term used for magma once it has erupted onto the Earth's surface |
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| a PASSIVE eruptive style volcano who's melt source is oceanic crust/mantle,has low silica content and viscosity, and contains a basalt rock type ~ Ex.-Hawaii |
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| an EXPLOSIVE eruptive style volcano who's melt source is continental crust, has high silica content and viscosity, and contains andesite and rhyolite rock types ~ Ex.-MountSt.Helens |
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| -Broad Cones -Gentle sloping sides -Low Si, High Fe & Mg. - Basalt |
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| -Narrow cones -Steeply sloping sides -High Si, Low Fe & Mg. -Andesites & Rhyolites |
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| a gas poor composite volcano ~ Ex.-Mount Lassen |
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| a gas rich shield volcano ~ Ex.-SP Crater |
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| C.V.'s are comprised of ... |
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| Alternating layers of tephra and lave from many series of eruptions [Seq. - 1)Tephra 2)Lave 3)Repeat] |
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| a catch all term for solid material of all sizes explosively ejected from a volcano into the atmosphere |
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| pertaining to fragmented (clastic) rock material formed by a volcanic explosion/ejection from a volcanic vent |
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| fragments less than 2 mm. in diameter of lava/rock blasted into the air by volcanic explosions |
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| So why do C.V.'s have alternation layers? |
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Definition
| Because each layer represents an eruptive sequence: 1)As the magma nears the surface, the bubbles expand up to 1000 times. This causes magma to explode violently 2)The remaining lava is gas poor, thus it flows 3)Repeat |
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| a sustained, explosive eruption which forms a high, jet-like column of pumice and ash in the atmosphere |
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| How do Plinian Eruptions form? (4) |
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| -Silica rich magma rises from depth -Dissolved gases come out of solution & form bubbles -When the bubble % reaches 50 the magma froth blow itself apart, forming a mixture of pumice, ash, and rock fragments dispersed in gas -This mixture then accelerates to the surface & erupts @ supersonic speed |
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| Give 3 Characteristics of Plinian Eruptions. |
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| -commonly last several hours -lay down thick layers of pumice as pyroclastic fall deposit -may reach well into the stratosphere |
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| a hot, dry, fast-moving and high-density mixture of ash, pumice, rock fragments, and gas formed during explosive eruptions or from the collapse of a lava dome. (aka nuee ardente) |
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| a pyroclastic flow consisting predominantly of ash-sized particles |
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| ash falling from an eruption column or ashcloud |
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| a flowing mixture of water-saturated rock debris that forms on the slopes of a volcano, and moves downslope, sometimes referred to as 'debris flow' or 'mudflow' |
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| earthquakes commonly provide the earliest warning of volcanic unrest, & earthquake swarms immediately precede most volcanic eruptions |
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| a continuous rhythmic earthquake that indicates motion of magma below the surface |
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| A Typical Earthquake Occurs When... |
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| when ground motion from upward moving magma displaces the land |
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| changes in gas composition or the emission rate may be related to variation in magma supply rate, change in magma type, or modifications in the pathways of gas escape induced by magma movement |
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| measurement of the changing shape of the volcano surface caused by the pressure of magma moving underground |
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