The reason astronomers like Hawaii is their volcanos. Volcanos provide the perfect place for placing telescopes, especially the ones rising from the ocean floor, far away from the land. The summit of Mauna Kea, almost 14,000 ft (4,200 m) above sea level, has a very dry, stable atmosphere, above the layer of clouds constantly covering the island at lower altitudes. Except for the lights coming from Honolulu in the distance, the night is very dark. That makes Mauna Kea the second best place in the world for astronomical observations (the best one is the high altitude plateau in Antartica).
As it often happens, placing large telescopes on top of mountains is not without controversy. If you have been on the summit of a mountain, you know the sense of awe that it inspires. This is even more true in the case of volcanos, where the landscape is shaped by creative forces of unparalleled power. Many native Hawaiians consider the summit of Mauna Kea a sacred place, and the giant telescopes a desecration. This sentiment has gone stronger in recent years, as the summit become filled with the many domes that house the astronomical instrumentation, and has currently stopped some of the projects for the development of new telescopes.
Mauna Kea is a dormant Volcano, its last eruption 3,500 years ago. The hotspot in the Earth mantle that is responsible for the creation of the Hawaiian islands chain has move east, and is currently causing the eruption of Kilauea, the last incarnation of Pele, the hawaiian goddess of fire. Kilauea is the most active volcano in the world, with the currently ongoing eruption starting more than 22 years ago. The photo above shows the main crater of Kilauea, site of many volcanic manifestations, like sulfur and vapor vents, while the main eruption proceeds at lower altitude, with a river of lava running from the side of the volcano into the ocean.
I took the photo from the south rim of the crater. There was a strong wind, and clouds and fog were filling the crater for most of the time, and the rain was making the hike quite miserable. When I had almost given up taking my crater shot, the landscape suddenly cleared, a hole opened in the cloud cover, and a ray of bright sun light hit directly the crater, creating on of the most amazing rainbow I have ever see. Like a rainbow on the moon.