Fire and Dust
||edHelper's suggested reading level:
||grades 9 to 10
||Flesch-Kincaid grade level:
||lapilli, pahoehoe, ropy, silicate, analysis, solidify, whey, stratovolcanoes, blocky, occurrence, viscosity, composition, felsic, mafic, geologists, funnel-shaped
||In Latin, Hawaiian Islands, Crater Lake, Mount Mazama
Print Fire and Dust
Fire and Dust
By Trista L. Pollard
|A force of thousands,|
Thrust toward the air
Tiny particles, too small to stare
Each unique and full of text
Of the Earth's anger, fire, and vex
2 The beauty and danger of nature is witnessed by geologists, volcanologists, and seismologists every day. The lava, fire, and dust that is sent into our atmosphere after volcanic eruptions provides scientists with valuable information about the Earth's interior. After eruptions have occurred, scientists study the composition of volcanic rocks to learn about our planet's crust and mantle. Based on their analysis, they have classified magma into two different types called mafic and felsic. Mafic magma or rock contains magnesium and iron. This magma is usually dark in color. Felsic magma or rock is composed of silicate minerals and has a light color. The Earth's oceanic crust is mostly made of mafic rock. The continental crust has both mafic and felsic rock.
3 Scientists have also learned that there are different types of volcanic eruptions. Magma's viscosity or resistance to flow, affects the force of a volcanic eruption. The composition of magma determines its viscosity. Quiet eruptions occur in oceanic volcanoes which are formed from mafic magma. The lava from mafic magma tends to be runny and have low viscosity. Since the magma has a low viscosity, gases are able to escape very easily. As a result, the eruptions from these volcanoes tend to be quiet. The oceanic volcanoes located in Hawaii tend to have quiet eruptions. Explosive eruptions occur most often in continental volcanoes. These volcanoes produce felsic lava that is sticky, cooler, and has high viscosities. There are large amounts of trapped gases like water vapor and carbon dioxide. Once these volcanoes erupt, the lava's dissolved gases escape and send molten and solid particles into the air. Both quiet and explosive eruptions send different types of rock material onto the surface and into the air.
4 Mafic magma produces lava flows. The movement of the lava and its rate of cooling affect the appearance of the lava flow. As the mafic magma cools rapidly, the lava flow forms a crust on its surface. During the crust formation, the lava may continue to move. This causes the crust to wrinkle, forming pahoehoe (pah HOH ee HOH ee) a type of volcanic rock. This type of rock forms from hot lava that is fluid. Once the lava cools, the pahoehoe forms a smooth ropy texture. The Hawaiian word for "ropy" is pahoehoe.
5 Aa (AH AH) is a type of volcanic rock that forms when the crust deforms rapidly or becomes too thick. Once the crust becomes too thick, it does not form a ropy texture. Instead, its surface breaks into jagged chunks and forms the texture of aa. The lava that forms aa has the same composition as the lava that forms pahoehoe. Its texture is determined by the differences in its gas content and the rate and slope of the lava flow.
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