EOSC 114 - Volcanoes

Any subsurface body of melt / crystals / bubbles / rock fragments resulting from melting of rock (gases dissolved and exsolved).

Masses, sheets, or other bodies of magma at the Earth's surface?

By the melting of pre-existing rock in the Earth's interior (mantle & crust).

- Units: g cm -3 or km m -3.- Becomes less dense with rising temperature.- Becomes more dense with cooling and pressure.

- The resistance to flow.- Controls the flow, deformation, and eruption of magma. - The composition of the magma affects the viscosity (especially H2O). - There is a higher viscosity (gooey) when it is cooler, and more dense. - There is a lower viscosity (runny) when it is hotter and less dense.

They crystallize and exsolve volatiles (gases).

- Rocks that come from felsic magma.- Contain high silica content.
- Rich in low density minerals.- Low density.- E.g: Granite, Rhyolite.

- Rocks that come from mafic magma.- Contain low silica content.
- Rich in denser materials.- Dark color.- Denser.- E.g: Gabrro, Basalt.

- Magma that freezes in the crust and is never erupted.- Slow cooling, large crystals.

- Magma erupted at the surface.- Quick cooling, tiny crystals or glass. - E.g: Basalt, Rhyolite.

- When there is a larger silica content (65-75%).- When it is cool (600-1000 C).- When there is higher viscosity. - When it is felsic.

- When there is a smaller silica content (25-55%).- When it is hot (1200-1400 C).- When there is lower viscosity.- When it is mafic.

- Basaltic lavas with low viscosity and high eruptive temperatures that move a few kilometres per hour which harden with a smooth commonly ropy surface texture.

- Cooler, more viscous basaltic lava flows that move only a few meters per day and harden with a rough, blocky surface texture.

- Hot spots (Hawaii, Long Valley, Yellowstone).- Mid-ocean ridges (Iceland).- Continental rift zones ( East Africa). -