TV Commercial for Yellowstone Park [in the mode of Saturday Night Live]
Husband: Yellowstone – it’s a volcanic caldera so big you can only see it from space!
Wife: No, it’s not! Yellowstone is family fun in the world’s oldest national park!
Announcer: Hey, hey, hey, calm down, you two. Yellowstone is both a Recreation Area and an Active Volcano!
Most of the two million tourists to visit Yellowstone each year don’t realize it, but they’re standing on top of the largest, most destructive type of volcano on Earth.
Beneath them lies an active magmatic (molten rock) system, the largest in North America. It produces the world’s largest and most diverse collection of geysers, natural hot springs, mud pots, and steam vents.
[University of Utah - Yellowstone GIS]
IMAGES [top to bottom]
 The geology behind the surface appearance of the Yellowstone Caldera (A) Confined pressure (B) water Table drops, which fragments the overlying rock and propels it upward (C) explosion of mud, steam, and water until a drop in confining pressure and steam lessened (D) a crater remains and fills with water. [source]
 Aerial view
 Aerial view of Grand Prismatic Hot Springs,
approximately 250 by 300 feet (75 by 91 m) in size.
In the center, steam rises from hot and sterile deep azure blue water. The open water is surrounded by huge mats of brilliant orange algae and bacteria, color varies due to to the ratio of chlorophyll to carotenoid molecules produced by the organisms.
During summertime the chlorophyll content of the organisms is low and thus the mats appear orange, red, or yellow. However during the winter, the mats are usually dark green, because sunlight is more scarce and the microbes produce more chlorophyll to compensate, thereby masking the carotenoid colors. [Wikimedia]
 The Geology of the Yellowstone Caldera: what makes it all happen
Cross section of the crust under Yellowstone showing the ring faults where a lot of the earthquakes and growth of the domes occur. (source)
Wikipedia: Yellowstone Hot Spot || Yellowstone Caldera