MAGMA IS FORMED DUE TO:

Increasing temperature
Decreasing pressure (pressure-release melting)
Addition of water

NOTE:

Water lowers the temperature at which the magma solidifies.
As magma loses water, its solidification temperature rises.

Elements of Magma

Elements: Si, Al, Fe, Ca, Mg, Na, K, H, O
Compositional variation: SiO2 (45% - 75% by weight), Al2O3, CaO, MgO, FeO, and H2O
Dissolved gases (0.2% to 3%): water vapor and CO2
Melting temp.: 800°C to 1400°C
Viscosity of the magma depends on its silica content
High Si = more viscous

Kinds of Magma

1. Basaltic MAgma

Remains liquid and rises to the surface to erupt.

50% silica; 1% - 2% water

less viscous

flows or rises easily

remains liquid since water loss is relatively unimportant

3. Granitic Magma

70% silica; up to 10% water

viscous magma

rises slowly

water loss cause it to solidify within the crust

Types of Lava

1. Dark-colored and contains a lot of water

rich in iron and magnesium; forms basalt

2. Light-colored and contains very little water

contains iron, magnesium, and silica; forms rhyolite
(resembles granite)

3. Chemical composition similar to that of the dark-colored and
light colored type

forms andesite

4. Contains large amount of gas such as steam and CO2

forms pumice and scoria with many holes in them