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.
They hope the lava will stay in the channels and not flow over the houses. There are a lot of factors that cause lava to be different - temperature, chemical composition, and amount of pressure all contribute to different types of volcanic flows. Just by looking at the lava thousands of years after the eruption, you can see exactly what type of flow it was.