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Sizzling Sites We started our tour with Old Faithful. You may not know much about geysers or hot springs, but this is the place to learn. T ere are more geysers and hot springs here than anywhere else in the world. A hot spring is a pool of water that’s been


heated below the surface. I bet you can guess how the water gets warm. Hot springs are made from rain or melted


snow. T is water seeps deep into the ground through cracks in the rock. Eventually, the water reaches that hot spot right above the magma chamber, and it heats up. T is superheated water rises slowly back


toward the surface to form a hot spring. T is cycle is repeated again and again. Many of the springs are ringed with color,


like brilliant yellow, orange, red, and green. T ese colors come from bacteria and algae living around the edges. T e blue water in the center is deep and clear. I’ve told you about the biggest hot spring


here. Yet there are many others. T ey glisten like jewels across the park. As you discover these, you’ll probably come across some geysers, too.


Gushing Geysers A geyser is a kind of a hot spring. Yet instead of the water slowly and gently rising to the surface, a geyser bursts from the ground as a steamy fountain. More than 300 geysers erupt here. T at’s more than half of the total number of geysers on Earth. Heat, water, and plugged-up plumbing


cause geysers to erupt. Water travels through rock by way of the many small cracks in Earth’s crust. Traveling through this plumbing system is not always a smooth ride, though. A narrow pathway can slow down the water. Trapped water grows hotter until it becomes superheated and changes into steam. T e steam erupts as the geyser shoots water into the air. T e geyser keeps spewing until it uses all of its water and the pressure drops.


20 NATIONAL GEOGRAPHIC EXPLORER


Right on Time As the pressure drops, the geyser settles down. Yet more water enters the plumbing system. Soon, that water is heated, fl ashes into steam, and erupts again. It’s a predictable pattern that scientists like myself have come to rely on when studying geysers. T at’s how Old Faithful got its name. It


erupts roughly every 90 minutes. Other geysers are predictable, too. Plume Geyser currently erupts every 30 minutes. Riverside Geyser erupts every 6 or 7 hours. Steamboat Geyser, the tallest in the world, may not erupt for years. Some geysers interact with one another.


Grand Geyser and Turban Geyser share some of the same plumbing. Grand Geyser erupts every 6 to 15 hours. A minute or two before or aſt er it does, Turban Geyser erupts.


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