Sulfur Banks
Sulphur Banks Trail starts near the Volcano Art Center. After a short hike through rainforest, you will soon emerge into a clearing where the Sulphur Banks are located. Here, sulfur and other minerals are deposited by gases rising from deep inside the volcano. The rocks have a green and white color due to the sulfur. There is also a distinct sulfur odor radiating from the banks. The rocks appear this way due to hydrothermal alteration. The gas that originates from the volcano is sulfide which oxidizes with groundwater and dissolves rocks (especially the iron in them) and bleaches the rock by hydrolysis. This sulfide gas is coming up from the magma chamber because of the ring fracture of the Kilauea caldera.
http://www.fireworkstudios.com/explore.html
Karen and Steve at the sulfur banks.
Photo courtesy of: Thom Wilch
Crystals of native sulfur precipitate on the rocks when the gas reaches the surface. Other minerals, including gypsum, opal, and hematite, form by the weathering of the rock and the precipitation of gases. Gypsum and opal occur as white coatings on the rocks. Hematite is red, like the rust on a car, and stains the rocks. (http://volcano.und.nodak.edu/vwdocs/Parks/hawaii/crater_rim_drive)
Sulfur stains on basaltic rocks.
Photos courtesy of: http://volcano.und.nodak.edu/vwdocs/Parks/hawaii/crater_rim_drive