Lava is hot melted rock found when a volcano is erupting. It comes from deep inside the earth where there is a lot of heat. Lava can reach temperatures from seven to ten times as hot as boiling water. There are many types of ways for lava to flow. Two common types of lava flows are called by Hawaiian names, "Pahoehoe" and "aa" because they come from volcanoes in Hawaii. Pahoehoe has a smooth rolling surface. Aa lava has a very rough surface. Both Pahoehoe and Aa lava are mostly made of basalt. There is a type of lava called basalt which is a dark grey or black color.

Lava made from andesite makes smooth-sided blocks of lava. Blocks are formed by andesite because it is less viscous than basalt. That means that it is thicker and cools off slower than basalt. The thick andesite lava flows slowly. Strato volcanoes usually erupt lava made of andesite. Lava domes are made of andesite lava.

Dacite and ryolite lava flows are the slowest flowing lava. They are very thick and viscous. These kinds of lava erupt from strato volcanoes and can be very explosive. Large amounts of gas gets trapped in the thick lava and cause very violent eruptions. When the ryolite lava cools it forms a black glassy lava field.

Most lava is made up of basalt. Basalt lava has less gas in it than lava made up of other substances like andesite or rhyolite. Basalt lava is thinner than other kinds of lava, so it flows faster than most other kinds of lava. Gases from inside the volcano can rise to the surface of basalt lava easily. That means that huge amounts of gas do not collect and cause severe eruptions. These kinds of eruptions with basalt lava means that the eruption is not too severe, but there is a lot of lava that flows out of the volcano's vent.

The thin basalt lava has a low viscocity rate. That means that it is runny and thin. Other kinds of lava have higher viscocity rates. That means that they are thicker and could have big pockets of gas. The more gas that is trapped in lava means that the eruption will be more violent.

A volcano's effusive rate is determined by the kind of lava and how much flows out of the volcano during an eruption.

Lava is called magma or molten rock before it comes out of an active volcano. Lava makes many different kinds of formations as it flows and begins to dry.