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Water and steam
7—Some of the minerals in the water are deposited around the geyser to build up the cone.
6—The steam and water shoot out of the geyser until there is no steam left.
5—Eventually, the pressure gets so high the water begins to boil. This causes cold water to be thrown out as a fountain, along with the hot water that has turned to steam.
4—The weight of cold water seeping into the upper passageway from above acts like a lid on a pressure cooker. The water below gets hotter and hotter, but it cannot escape.
3—Heated passageways continue to heat the trapped water.
2—Water heats up to above boiling point in a chamber created where rock has been dissolved away.
1—Water seeps through the rocks and builds up in underground passageways.
 Geyser—The seven stages of geyser activity.
2,000m to 3,000m from surface to lowest collecting chamber.
 Geyser—Castle Geyser, Yellowstone National Park.
Glass, volcanic
Lava that has solidified very quickly and has not had time to develop separate crystals properly. Obsidian is a volcanic glass.
Chamber
Chamber
Glass, volcanic
 Glass, volcanic—Obsidian is a natural glass. It is opaque because the glass contains a huge number of natural flaws.
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