Lava or molten rock is made by an active volcano at the time of eruption. Lava is made up of volcanic glass and gases, and crystals. At the time of eruption, this molten rock is liquid at a temperature of 700-1200 °C, but as it approaches the surface, it cools and crystallizes minerals to form crystals and gases. Some of the elements that are found in lava and igneous rocks are silicon, oxygen, aluminium, iron, potassium, calcium, magnesium, calcium, phosphorous, titanium and others in small amounts.
The word lava is derived from a Latin word “labes” which means to slide. Lava flows during a non-explosive eruption and when cool, forms igneous rocks. Rocks are made up of combinations of different elements and their oxides in different compositions. If the eruptions from the volcano are explosive, it produces volcanish ash.
The flow of lava is largely determined by its composition. Igneous rocks falls into three categories, felsic, intermediate and mafic. The chemical make up, temperature and viscosity of these rocks are slightly different.
Felsic lava is viscous and form lava spines and domes. This type is high in silica, aluminium , potassium, sodium and calcium. Examples of this type of lava include rhyolite and dacite. Intermediate lava is less viscous and found in steep volcanoes. This type is rich in magnesium and iron and poor in aluminium and silica. Andesitic is intermediate lava. Mafic lava is high in iron and magnesium and darker in color and less viscous. It is also called basaltic lava.
If the lava contains less percentage of silica, it is known as ultramafic lava, which is a rare type of lava. Due to the least viscosity, this type of lava is more fluid than the mafic lava.
The composition and viscosity of lava determines its behavior. Lava with high viscosity flows slowly, forms blocks. This type tends to trap gases within the rock. Low viscosity lava flows easily, and forms rivers of molten lava. It does not trap gases as the former type.
Lava forms distinct landforms and features depending on its viscosity and flow. They form cones around a small vent or volcanic edifice, domes, when very viscous lava is released, tubes, lava fountains, and lakes. Lava flow is destructive to property and releases poisonous gases harmful to man and animals. Before a volcano becomes active, the area around it is usually evacuated.