- A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
- Incredible Moiré Patterns! (youtube.com)
Sir Roger Penrose demonstrates the extraordinary moiré patterns produced by overlaying and rotating two identical, repeating patterns. As the two patterns overlapped and rotated they interfere with each other to produce tertiary patterns.