Geology Volcanoes&Earthquake Assignment8 Assignment

Geology Volcanoes&Earthquake Assignment8 - Assignment Example An inevitable tide was moving red-hot lava onshore and people watched helplessly. However, a small crew led by Thorbjorn Sigurgeirsson squirted the lava in the front with fire hoses producing vapors of steam (John A. McPhee. 102). The courageously watered and cooled the advancing lava until they stopped the lava flow (John A. McPhee. 107) The gas content in magma or lava determines whether a volcanic eruption will be explosive or effusive. These gases include sulfur dioxide, water vapor and carbon dioxide. A gas highly dissolves in magma that is situated deep underground, where pressure is very high. The rate of dissolution decreases as the lava moves up to the earth’s surface due to reducing pressure, thus, the gas form bubbles that drag magma to the surface. The eruption is explosive if more bubbles form and effusive when there are few bubbles. A cinder cone forms when lava with more bubbles is expelled and cools in the air (Gates and Ritchie p.157). Magma comprises of solid minerals, liquid rocks and gas. The amount of the silica mineral in lava or magma determines a volcanic rock to be formed. The mafic rocks include all basalts and some andesites: have lower silica content, intermediate rocks such as some dacites and most andesites with intermediate silica content, and silicic rocks. Silicic rocks have higher silica content and include all rhyolites and some dacites. Apart from silica, volcanic rocks have other minerals such as titanium, aluminum, iron, manganese, magnesium, calcium, sodium, potassium, and phosphorus. These chemicals are mix with oxygen to form their respective chemical compounds (Park, 2001, p. p.177). A magma viscosity determines a volcano shape, texture and shape of lava, and whether a volcano erupts effusively or explosively. A less viscous lava forms shield volcanoes with wide sloping sides while more viscous lava builds conical volcanoes with steep sides.