A lil about how its created...

Yellowstone National Park sits atop a hot spot, which is responsible for the creation of many of the geographic features of the park. As the North American plate moved over the hotspot, a series of volcanic eruptions left behind a trail known as the Snake River Plain. 

                                                               Topographic map of the Snake River Plain

 (http://www.google.com/imgres?imgurl=http://volcano.oregonstate.edu/vwdocs/vwlessons/hot_spot_pics/SRP_Thematic_Map.gif&imgrefurl=http://volcano.oregonstate.edu/vwdocs/volc_images/north_america/yellowstone.html)

One of the violent eruptions caused the overlying land to collapse and resulted in a geographic depression known as a caldera. Yellowstone is known for its geothermal activity such as geysers and hot springs, which is caused in part by the large chamber of magma under the calderas' surface heating the recirculation ground water. 

(http://www.geology.sdsu.edu/how_volcanoes_work/Thumblinks/yellowstone_page.html)

                                                                               A Yellowstone hot spring

(http://www.google.com/imgres?imgurl=http://media.away.com/images/ideas/rockies/yellowstone-national-park.jpg&imgrefurl=http://www.gorp.com/parks-guide/travel-ta-trekking-backpacking-wyoming-hiking-yellowstone-national-park-gardiner-fishing-sidwcmdev_059157.html)

The magma chamber is inflating, which stretches the crust above the chamber, causing extension faulting like at Mirror Lake. Pressure from the magma below has caused the land at two faults to snap and the area between them is depressed, which is called graben. On the west side of this graben, fault scarp is visible. Mirror Lake is also a sagpond, and fills a depression in the uneven ground at one of the faults. 

                                   Mirror Lake and the graben resulting from the two faults

(http://www.google.com/imgres?imgurl=http://volcanoes.usgs.gov/yvo/images/1992-rbs-aerialmirror_large.jpg&imgrefurl=http://volcanoes.usgs.gov/yvo/images/1992-rbs-aerialmirror_caption.html)

                              Fault scarp at Mirror Lake

 (http://volcanoes.usgs.gov/yvo/images/1992-rbs-aerialmirror_caption.html)

These volcanic systems unfortunately produce 1000-3000 earthquakes a year, which can be devastating to the humans inhabiting the region.

                                            Earthquakes in Yellowstone from 1973-2001

(http://scienceblogs.com/eruptions/2010/02/the_structure_of_calderas.php)

http://www.answersincreation.org/curriculum/history/earth_history_c14_yellowstone.htm

http://www.nps.gov/yell/naturescience/smithtranscript.htm

  http://volcanoes.usgs.gov/yvo/images/1992-rbs-aerialmirror_caption.html