Lava is molten rock expelled by a volcano during an eruption. Below the earth`s surface, molten rock is termed magma instead of lava. Lava, when first exuded from a volcanic vent, is a liquid at temperatures typically from 700 °C to 1,200 °C (1,300 °F to 2,200 °F). Although lava is quite viscous, about 100,000 times the viscosity of water, it can flow great distances before eventually cooling and solidifying.
Lava solidifies to form igneous rock. The term "lava flow" refers to the hardened formation, whereas the one still having molten rock associated, is called an "active lava flow".
Lava Flow is an outpouring of lava onto the land surface from a vent or fissure. Also, a solidified tongue like or sheet like body formed by outpouring lava.
In general, a lava`s composition determines its behavior more than the temperature of its eruption. Igneous rocks, which form lava flows when erupted, can be classified into three chemical types; felsic, intermediate, and mafic. These classes are primarily chemical; however, the chemistry of a lava also tends to correlate with the magma temperature, its viscosity and its mode of eruption.
The viscosity of lava is important because it determines how the lava will behave.
Highly viscous lava shows the following behaviors:
· It tends to flow slowly, clog, and form semi-solid blocks which resist flow
· It tends to entrap gasses, which form bubbles within the rock as they rise to the surface
· It correlates with explosive or phreatic eruptions and is associated with tuff and pyroclastic flows
Highly viscous lavas do not usually flow as liquid, and usually form explosive fragmental ash and cinder deposits. However, a degassed viscous lava or one which erupts somewhat hotter than usual may form a lava flow. Viscous lavas have two forms of non-pyroclastic eruptions, lava domes and sheeted flows.
Lava with low viscosity shows the following behaviors:
· It tends to flow easily, forming puddles, channels, and rivers of molten rock
· It tends to easily release bubbling gases as they are formed
· Eruptions are rarely pyroclastic and are usually quiescent
· Volcanoes tend to form as rifts, not steep cones