A lava flow is caused by a volcanic eruption. The lava can flow down the volcano at speeds ranging from 1/24 to 50 meters an hour. They can be 1,300 degrees fahrenheit or more. They are very destructive.
The theory on how volcanoes erupt
The theory is that pressure and other factors in the gas cause some upward pressure. Magma is formed when the earth’s upper crust melts (for some bizarre reason it’s magma under the earth and lava above). The magma falls down with gravity and is pushed up with the pressure of the gases. When the pressure gets high enough the magma shoots out of the volcano turning it into lava.
Pyroclastic eruptions are formed when water and other gases get dissolved into the magma. The magma rises and the water separates. When the ratio of the gases is more in the magma it disintegrates into a combination of mostly rocks and a little bit of lava, and the volcano erupts explosively.
Pahoehoe lava flows very smooth and thin. They are about 1-2 meters thick and go up to 50 meters an hour. They are formed by liquid basalt. They move in “tongues” and can be identified by their smooth glassy skin. When the Pahoehoe cools it has a smooth surface
Sheet lava is usually 10 to 30 meters thick. They are very fast. They also tend to fill in low lying areas or pool in them. Almost always the top part of the lava cools first. The interior can stay lava for a long time. Sometimes, the liquid lava trapped beneath the hardened crust continues to flow, leaving an empty tube. The top crust can eventually break open, exposing the tube.
A’a flows can come out of the volcano up to 50km per hour. They can push down houses, walls, and forests. When it cools it is sharp and broken into many pieces called clinker. It can be dangerous to walk over because it’s so sharp. The clinkers can range from 1cm to 1m in size.
Block lava is thicker and slower than a’a lava. They move at 1 to 5 meters a day. When they solidify they often make cube like structures that are rather smooth. They are more viscous than a’a lava flows. Block lava is solidified much like sheet lava. Read more about how volcanos form and types of lava.