West Thumb

West Thumb Geyser Basin is a caldera with in a caldera, meaning it is the vent of a volcano inside the crater of a much larger volcano. About half the area of Yellowstone Park, including all of Lake Yellowstone, is the big crater (or "caldera") of a giant volcano that last erupted about 640 thousand years ago. West Thumb crater itself is the remants of an eruption inside the Yellowstone caldera that last occurred about 150,000 years ago.

This is a view of West Thumb Basin.

There is a short easy boardwalk hike around the West Thumb geothermal features. You can see everything at a leisurely pace in about an hour or two. This is Percolating Spring.

There is a mud pot at West Thumb, and the consistency of the mud allowed the bubbles to slowly grow before popping. I tried to capture a "pop" with my camera.

Bluebell and Seismograph Pools. These used to be called simply "The Blue Pools", but after the 1959 earthquake (7.5 on Richter scale), one of the pools became murky. Bluebell pool is in the background.

This is Lakeshore Geyser. Too bad we didn't see this erupt. However, it has been dormant for years now, except for boiling the lake water. The lake water boils when it covers the surface of the geyser vents. Water level in Lake Yellowstone varies due to snow melt.

Fishing Cone geyser was used to cook fish that had been caught in the lake. Apparently, too many tourists scalded themselves attempting to pose for photographs, so now you not allowed to walk up to the cone.

Abyss Pool is a very deep, very hot spring. It had a few periods in its history where it erupted dramatically, up to 100 ft, but now it is quiet.

Black Pool is another very hot, deep pool that has erupted in the past but now quietly steams.

Blue Funnel Spring got it's name because the rim of the pool appeared to be bluer in color compared to the rest of the water. But water level in this spring fell when Abyss Pool entered a period of activity, and that altered the appearance. All the geothermal features in Yellowstone are constantly changing. I guess that makes the predictable nature of Old Faithful even more amazing.