Images

National Agriculture Imagery Program natural-color image from September 9, 2006, showing newly mapped thermal areas (outlined in yellow) on the north side of the Mallard Lake resurgent dome.

Guardian Geyser and Norris Geyser Basin, Yellowstone National Park.

Aerial view of Excelsior Geyser (in the foreground) and Grand Prismatic Spring in Yellowstone’s Midway Geyser Basin. The colors around the thermal features are locations of different thermophile communities. These thermophiles fix carbon, both from the atmosphere and from the hot water. Credit Jim Peaco; June 22, 2006; Catalog #20386d; Original #IT8M4075

Old Faithful Geyser in eruption. Under Yellowstone Research Permit YELL-SCI-8030, 13 mineralized wood specimens were collected from the geyser mound. The dates of the mineralized wood samples imply that such eruptions did not take place for over a century between the mid-13^th to mid-14^th centuries.

Rangers attempting to clean trash out of Morning Glory Pool in September 1975. National Park Service photograph Dan Ing.

A comparison of black cinders from Cinder Pool, in Norris Geyser Basin (left), with yellow cinders from an unnamed pool in the West Nymph Creek thermal area (right).  The Cinder Pool cinders are black due to finely dispersed pyrite, whereas the yellow color of cinders from the West Nymph Creek pool is due to the lack of pyrite.

Aerial (balloon) view of Norris Geyser Basin, Yellowstone National Park, looking northwest from the south.  USGS Photo by Brita Graham Wall, 2005.

Grand Prismatic Spring, Midway Geyser Basin, Yellowstone National Park.  Grand Prismatic is the largest hot spring in Yellowstone and the third largest in the world. Photograph by Robert Fournier.

Eruptions of the Yellowstone volcanic system have included the two largest volcanic eruptions in North America in the past few million years; the third largest was at Long Valley in California and produced the Bishop ash bed. The biggest of the Yellowstone eruptions occurred 2.1 million years ago, depositing the Huckleberry Ridge ash bed.

Heise cliffs, the type location for the 4.45–7.0 million year old Heise Group from the Heise volcanic field, which preceded the Yellowstone Plateau volcanic field.  Most of the cliffs exposed here are rhyolitic, densely welded, rhyolitic pyroclastic density flow deposits.  USGS Photo by L. A. Morgan (May 2005).

Map showing earthquake focal mechanisms in the Yellowstone region.

Exposure of rhyolite volcanic rocks in the central Snake River Plain showing a thick sequence of 10-12 million-year-old, densely welded, pyroclastic density flow units (darker units from middle of photo to top of hill) overlying a thick sequence of white, friable, ash fall deposits.  USGS Photo by L. A. Morgan (May 2004).

Densely welded rhyolites from the central Snake River Plain.  USGS Photo by L. A. Morgan (May 2004).

Slow cooling of a basaltic lava flow that was erupted about 500,000 years ago resulted in the formation of hexagonal columns at Sheepeater Cliff, in Yellowstone National Park.

Simplified geologic map detailing locations of volcanics at Sepulcher Mountain and igneous intrusion at Electric Peak and surrounding area. This map is Fig. 2.

Norris-2003. Location map of seismometers and GPS receivers deployed to help monitor the Norris Geyser Basin.

A 1.5-million-year-old basaltic lava flow in the canyon wall of the Yellowstone River as viewed from Calcite Springs Overlook near Tower Junction in Yellowstone National Park.  Slow cooling of this lava flow resulted in the formation of vertical columns.  Glacial gravels are present above and below the lava flow.

Angel Terrace, Mammoth Hot Springs, Yellowstone National Park. Travertine deposits are abundant in the area. Photo by JoAnn Holloway, 2003.

View to the southeast through the area affected by the increased thermal output at Norris' Back Basin in the summer of 2003. The foreground shows steaming areas where boiling water and steam have approached the surface, resulting in increased ground temperatures.

Bathymetric map of Yellowstone Lake showing hydrothermal features in the north part of the lake, including Elliott's Crater, Mary Bay, and Deep Hole.  Colors correspond to lake depth, with cooler colors indicating greater depths.

Criteria for estimation of the Volcanic Explosivity Index (VEI).  Modified from: Newhall, C.G., and Self, S., 1982, The volcanic explosivity index (VEI): An estimate of explosive magnitude for historical volcanism. Journal of Geophysical Research, v. 87, no. C2, p.