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Facts About Lava Flow

At a root zone of 40 to 70 miles below the earth's surface, temperatures are high enough to melt rock and form magma, which becomes lava when it reaches the surface. Magma is far less dense than the solid rocks surrounding it, and gravity forces the magma to the earth's surface. Once lava reaches the surface, the material ranges from being very stiff and stagnant to very fluid and flowing.

Magma
- Lava is made out of molten rock formed deep below the earth's surface. Before this molten rock reaches the earth's surface, it is called "magma." The main ingredients of magma are crystals, unmelted rock and dissolved gasses. Magma also has traces of iron, oxygen, calcium, magnesium, silica and aluminum.
Types of Lava
- The particular composition of magma determines the rock type it will form when it cools. The three main rock types are basaltic, andesite and rhyolite. Basaltic flows have high temperature and low silica content, allowing them to travel quickly and far. Rhyolite lava has a highly dense chemical composition, with large amounts of potassium, sodium and silica. This type also has relatively low temperatures, making it the slowest flowing lava. Andesite lava is an intermediate between the other types, and its volcanoes are characterized by a cone shape.
Temperature
- The temperature of molten lava ranges from 1,300 to 2,200 degrees Fahrenheit, depending on the type of lava. The coolest type, rhyolite lava, has a low eruptive temperature of 1,472 to 1,832 degrees Fahrenheit. Basaltic flows range from 1,832 up to 2,192 degrees Fahrenheit.
Flow
- The speed of lava flow is determined by its viscosity, or its resistance to flow. The amount of viscosity depends on the lava's chemical composition and temperature. For example, very hot lava with low silica contents has very low viscosity and thus flows quickly. The amount of viscosity also determines the type of rock it will form upon cooling.
  
  Lava can flow very rapidly once it establishes channels in which to flow freely. Hawaii's Mauna Loa eruption in 1950, for instance, started out flowing at 10 kilometers per hour through a forest, and then sped up to 60 kilometers per hour after establishing a long channel. Other lava flows, such as Hawaiian pahoehoe lava, stop moving after minutes and quickly form into highly dense material capable of supporting considerable weight.

Nature