1. Integrated Science (H)
Volcanic Rocks
Mt St Helens, 1980
Integrated Science (H)

2. Background
Volcanic rock chemistry allows us to understand the nature of oceanic and continental crust. Additionally, it explains the behavior of lithospheric plates at subduction zones, and explains the distribution of volcanoes by magma type around the globe.
andesite
rhyolite basalt

3. rhyolite granite
Volcanic rocks are extrusive igneous rocks, formed from magma - melted rock - that cools quickly at the surface as it is ejected. (In contrast, intrusive igneous rock cools slowly within the crust.) These rocks vary in silicon oxide (SiO2) and iron oxide (FeOx) content, reflecting the chemical makeup of the magma they are formed from. Volcanic rocks build both oceanic and continental crust.

4. Oceanic crust is composed of basalt
Oceanic crust is composed of basalt. Basalt has low viscosity, and so forms thin lava that flows easily and spreads.
Mauna Loa, HI, continuous eruptions since 1989

5. Chaiten, Chile, 2008
Continental magma is granitic, forming rocks such as granite (intrusive) and rhyolite (extrusive). This magma is high in gases and very viscous, (resists flowing) a combination which causes explosive, rather than flowing, eruptions.

6. • Rank from highest to lowest density.
• Determine the density of basalt, andesite and rhyolite volcanic rocks Go to:
• Rank from highest to lowest density.
andesite
rhyolite basalt