Essentials of Geology 3 rd Edition Chapter 4 Norton Media Library
Up from the Inferno: Magma and Igneous Rocks Prepared by: Ronald Parker , Senior Geologist Fronterra Geosciences Houston, Oklahoma City, Denver, Anchorage, Dallas, Midland, Aberdeen, Vienna, Buenos Aires, Neuquén www.fronterrageosciences.com
Composition controls magma density, T, and viscosity.
The most important factor is silica (SiO 2 ) content.
Silica-rich magmas are thick and viscous.
Silica-poor magmas are thin and “runny.”
These characteristics govern eruptive style.
Type Density Temperature Viscosity Felsic Very low Very low (600 to 850 ° C) Very High: Explosive eruptions. Intermediate Low Low High: Explosive eruptions. Mafic High High Low: thin, hot runny eruptions. Ultramafic Very high Very high (up to 1300 ° C) Very low.