Kilauea Volcano. Advancing aa lava flow front in the twilight against red trees. Yellow flow from the east. Aa lava is produced when thick, slow lava cools and breaks, which forms cooled lava similar to bumpy rocks. Kilauea is one of the world's most active volcanoes. Lava reaches volcanoes from the Earth's interior through faults in the crust, and is forced through them by the high pressure within the Earth. The black rock of this coastline is made from old lava flows. Lava flows like this mean that the Hawaiian islands are still increasing in size. Photograph taken on 10/23/99.