the nature of volcanic eruptions: factors that affect ... · the nature of volcanic eruptions:...

types of volcanoes 2015 2016.notebook

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October 13, 2016

Nov 129:18 AM

The Nature of volcanic eruptions: Factors that affect viscosity.

Temperature:

The effect of temperature on viscosity is easily imagined. Imaging putting syrup in the refrigerator and then pouring it...now imagine putting hearing it up on the stove. What has the temperature done to the viscosity of the syrup? Of course, it had decreased it!

Nov 129:22 AM

Composition:

Remember the major difference between igneous rocks is their chemical composition, specifically how much silica they contain in their mixture. Magma's viscosity is directly related to its silica content because silicates start to link together in long chains early in the crystallization process. because of this, felsic (rhyolitic) lavas form thick flows that may flow as far as a kilometer or two (1.5 miles) whereas mafic (basaltic ) flows may travel 150 kilometers (90 miles) before solidifying

Nov 129:28 AM

Dissolved gasses:The gasses that are dissolved in magma is mainly water vapor. When magmas contain a lot of gasses, it can usually be kept in solution by the tremendous pressure of the overlying rock. As magma rises through conduits, or cracks created by the bulging of the magma chamber, the confining pressure is reduced causing the gasses to be to separate from the magma to form tiny bubbles (much like the bubbles form in soda when you release the pressure of the cap). As the volcano erupts the pressurized gasses steadily escape. At temperatures that readily exceed 900 degrees C, these gasses can quickly expand to hundreds of times their original volume. which can propel incandescent lava up to 40 kilometers (25 miles) into the air. Sometimes these explosive events throw particles of fragmented lava (ash and pumice) at nearly supersonic speeds creating buoyant plumes called pyroclastic flows.


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October 13, 2016

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October 13, 2016

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Fun fact:

The eruption of Tambora, Indonesia in 1815 is the largest known volcanic eruption in modern history. releasing more energy than 33 billion tons of TNT, or 2.2 million atomic bombs. It released more energy than the United States uses in one year (which is 1/4 of the world;s energy consumption). and the explosion was heard from 3,000 miles away.

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October 13, 2016

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Cinder cones (a.k.a. scoria cones)

As their name suggests, cinder cones form from ejected material from a violent eruption. The lava typically contains a lot of gas, and as it gets ejected into the air, it hardens in flight forming vesicular rocks like pumice and scoria. The pyroclastic fragments can range in size from fine ask and dust to blocks that are as large as a house!

Because cinder cones are composed of loose fragments rather than solid rock, they don't grow very big and are quickly eroded by weathering and erosion. Cinder cones range in size from 100‐1,000 feet

Most cinder cones are produced by a single, short lived eruptive event (in an interesting study, half of all cinder cones were formed in less than a month and 95% were formed in a year

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October 13, 2016

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Paricutin: A cinder cone volcano born in a mexican cornfield.

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October 13, 2016

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Cinder cones can form from continental hot spots, but they can also grow on the flanks of other volcanoes, in this case, they are called parasitic cinder cones. Hawaii has many parasitic cinder cones, and despite the basaltic lava the copious amounts of seawater that gets dissolved in superficial magma chambers cases the basalt to become highly eruptive, creating the "scoria cone"

Nov 1210:18 AM

The most picturesque, yet potentially dangerous type of volcano is a composite volcano. Most are found in a relatively narrow zone that rims the pacific ocean, appropriately called the Ring of Fire.

Nov 1210:21 AM

Classic composite volcanoes are large, nearly symetrical structures consisting of alternating layers of explosively erupted ash and cinders interbedded with lava flows. Just as shield volcanoes owe their shape to fluid basaltic lava flows, composite volcanoes reflect the viscous nature of the material of which they are made. In general composite volcanoes are a product of silica rich magma having an andesitic composition.


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October 13, 2016

Nov 1210:50 AM

Subduction = ANDESITIC

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Why? Think about the plates involved... a basaltic plate is melting and rising, as it rises, it melts through the continental (granitic) crust which is rich in silica. The combination and mixing of the two magmas creates an intermediate melt!


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October 13, 2016

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WOWIE

ZOWIE

Tambora was a type of composite volcano

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October 13, 2016

Nov 1211:55 AM

Shield volcanoesShield volcanoes consist of many successive layers of low viscosity basaltic lava and a lack of pyroclastic flows. Most shield volcanoes are associated with hot spot vulcanism.

Hot spots cause lava plumes. As mantle plumes move towards the surface, its hot temperatures quickly cause the mantle material to reach the crust. As this happens, the crust quickly melts creating massive amounts of lava to be released on the crust. The type of material produced is largly basaltic flows called Aa, Pahoehoe, and Pillow lava (basaltic flows in the water)

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October 13, 2016

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Lava tree!!!

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Rift eruptions are responsible for most of the shield volcanoes. This occurs at divergent plate boundaries

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