What does the ancient earthquake detector do? it help tell the direction of where it came from and the slightest movement will make the ball fall if you are referring to the ancient china one Edit
Depending on the type of lava flow, the resulting rocks look very different. This was a pahoehoe flow. 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.
As the bubbles escape, they push the magma out, causing a spewing eruption. The nature of this eruption depends mainly on the gas content and the viscosity of the magma material. Viscosity is just the ability to resist flow -- essentially, it is the opposite of fluidity. If the magma has a high viscosity, meaning it resists flow very well, the gas bubbles will have a hard time escaping from the magma, and so will push more material up, causing a bigger eruption.