The Caldera

Views from Norris Geyser Basin





Steamboat Geyser last erupted in 2005; Is 3 times higher than Old Faithful at eruption

Views from Black Sand Basin







The next stop in our busy day was on to the geyser basin which is inside the caldera. Basically, Yellowstone National Park sits on top of a supervolcano that is about 34 miles by 45 miles. Magma causes the ground to swell and deflate on a regular basis. Yellowstone experiences about 3000 earthquakes a year, most of which cannot be felt. The result of all the underground action is the hot springs, mudpots, fumeroles (steam vents), and the famous geysers.

Geysers are hot springs with narrow sapaces in the plumbing, usually near the surface which prevent water from circulating freely to the surface where heat would escape. The surrounding pressure increases with depth and with the enormous weight of the overlying rock which prevents the water from vaporizing. As the water rises, steam forms, bubbling upward,expanding as it nears the top of the water column until the bubbles cannot pass freely through constrictions. Tremendous amounts of steam force water out of the vents, and the eruption begins. Water is expelled faster than it can enter, and the heat and pressure gradually decrease. The eruption stops when the water reservoir is empty or when the bubbles diminish enough to be able to rise without spitting out the water. (Info taken from NPS/YNP publication)

These pictures are from the Norris Geyser Basin and from Black Sand Basin (which we actually visited on another day).