BY : Rhiannon Nevinczenko

It sounds like a waterfall.
You're standing cautiously some 300 or so feet from an inauspicious-looking cone of earth, at the center of a respectable radius of botanic infertility. Pressure rumbles from below, shooting thousands of gallons of boiling water far into the sky. These beautiful and dangerous eruptions keep all life forms at a safe distance, you included. It's like a little water volcano, and it sounds like a waterfall.
You are visiting Yellowstone National Park, watching a geyser erupt. Geysers are a unique and rare type of hot spring, distinguished from others by the way they erupt (rather than the subdued burbling demonstrated by most hot springs, sans drama). When Old Faithful erupts, for example, it can eject a maximum of 8,400 gallons of water up to 184 feet into the air. Geysers are rare because they can only form when three things combine: water, intense heat, and "plumbing" (a waterworks system). Volcanism tends to be necessary for this, as magma serves as the heat source. Thus, the surrounding rock is heated, boiling the water, increasing the pressure, and ultimately forcing the water up the earthen column. In other words, it is like a giant underground tea kettle. Water finds its way into these systems as precipitation (rain and snow) flows into the ground through fractures in the bedrock.
The geyser pictured here is Castle Geyser at Yellowstone National Park, nearby Old Faithful.
Image credit: USGS, public domain.

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