ESS 101 Lecture Notes - Lecture 3: Tuff, Amphibole, Aphanite

• School: UW
• Department: Earth and Space Sciences
• Course: ESS 101
• Professor: Swanson Terry

Document Summary

Magma is composed of liquid, solid (mineral crystals), and gas. Magma composition is largely controlled by its source. Magmas are subdivided largely by silica content: as silica content increases, iron and magnesium content decreases, note that lighter elements such as sodium and potassium content follow the silica trends. Elemental composition of magmas and rocks are described in terms of oxide composition because of their common bonds with oxygen. The viscosity (resistance to flow) of magma is controlled by silica content and temperature: high silica content and low temperature magmas tend to have higher viscosities. Rhyolite/dacite flows will retain steep front slopes because of their high viscosity. Basaltic magma is a dry melt (little dissolved water) and its melting temperature decreases with decreasing pressure (as the magma rises) As the basaltic magma further melts, its density decreases, causing it to continue to rise until it reaches the surface: note: the temperature of rising magma is.