Consider the following statements about natural phenomena.
1. Penitentes are formed in high altitudes where sunlight turns ice directly into water vapour rather than melting it to water.
2. During an eruption in volcanoes ash picks up so much friction that the build-up of static electricity causes lightning.
3. Salar de Uyuni is the world's largest salt flat at 10582 km2 and holds around half the world's reserves of lithium.
4. Fire rainbows are caused by fire or rain.
Which of the statements given above are correct?