Figure 1. NE caldera rim faults and Mirror Lake. Photograph courtesy of Bob Smith, 1992.
An aerial view of faults associated with the NE rim of Yellowstone Caldera is shown in Figure 1; view is looking southeast (arrow identifies direction of view in the bottom photograph). Lines mark top of fault scarps associated with the collapse of Yellowstone Caldera during enormous eruption about 640,000 years ago. Mirror Lake fills a depression due to uneven settling of the ground along one of the faults, called a sagpond by seismologists. The low area between the outermost caldera rim fault and the next fault is a graben. The two faults that straddle Mirror are good examples of antithetic faults, which are normal faults that are of the opposite orientation to the major fault with which they are associated (the outermost caldera rim fault). In this view, the right side (west) of the outermost fault has dropped downward; in the other faults, the left sides (east) dropped downward.
The snow covered Absaroka Mountains are visible in the far distance; Yellowstone Lake is in upper right. Access to this remote part of Yellowstone National Park requires special permission from the park.
Figure 1. NE caldera rim faults and Mirror Lake. Photograph courtesy of Bob Smith, 1992.
Figure 2. Ground view of outermost NE caldera rim fault near Mirror Lake. Photograph courtesy of Bob Smith, University of Utah, 2001.
Figure 2 provides a view of the outermost caldera rim fault from the top of fault scarp on the west side of the graben (see arrow in Figure 1). The fault scarp is about 30 m tall; note person on horse for scale (circle). Lava Creek Tuff covers the graben's surface.