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.
Eruptions of andesitic/rhyolitic magmas are generally explosive. High viscosity of intermediate/felsic magmas prevents most gasses from exsolving during magma ascent. Most gasses exsolve just as the magma reaches the Earth's surface, resulting in a large increase in gas pressure within the magma chamber.