Images

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

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.

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.

MODIS satellite image of New Zealand’s North Island acquired on October 23, 2002 (https://earthobservatory.nasa.gov/images/3101/new-zealand).  Lake Taupō is located in the center of North Island.

Benchmark T366, was installed in 1987 a few miles north of Canyon Junction in Yellowstone National Park. Rather than being a brass or aluminum disk, the benchmark is a rod that was driven into the ground until it would not sink any lower.  The precise elevation of the top of the rod was established by surveying methods, and an access cover flush with the g

Map of the northwestern U.S., showing the approximate locations of Yellowstone hotspot volcanic fields (orange) and Columbia River Basalts (gray). Boundary of Yellowstone National Park is shown in yellow. Modified from Barry et al. (GSA Special Paper 497, p.

Geological Map of the area around Monument Geyser Basin and Beryl Spring, taken from the Geological Map of the Yellowstone Plateau Area (Christiansen, 2001)

Interpretive reconstruction of the Yellowstone Plateau region before initial plateau volcanism (a little before 2 million years ago). The region was entirely an elevated and faulted mountainous terrain with no basin in the present plateau area.

Geologic map of the Yellowstone Plateau Volcanic field generated by Bob Christiansen and published in 2001.  Available from https://pubs.usgs.gov/pp/pp729g/plate1.pdf.

Left: Map of Yellowstone showing the extent of mapped Lava Creek Tuff members A and B, which erupted during the formation of Yellowstone Caldera about 631,000 years ago. Right: Geologic map of Madison Junction (1:125,000).

Scientist from the USGS collects a gas sample into an evacuated/vacuum flas from a steam vent near the Shoshone Geyser Basin.

Obsidian Cliff exposes the interior of a thick rhyolite lava flow erupted about 180,000 years ago. The vertical columns are cooling fractures that formed as the thick lava flow cooled and crystallized. The flow consists of obsidian, a dark volcanic glass.

View from the SE rim of McDermitt caldera, Nevada and Oregon, showing rhyolite lavas overlain by thin outflow McDermitt Tuff in the south wall of the caldera. The low area that makes up most of the photo is intracaldera tuffaceous sediment. This is Thacker Pass, the site of largest and highest-grade lithium deposits in the region.

Schematic illustration showing the 1912 Novarupta eruption in Alaska and the caldera collapse at Mount Katmai, 10.6 km (about 6.6 miles) to the northeast.

The history of Earth’s glacial and interglacial periods for the last 700 thousand years is reflected in the variation of oxygen isotope composition of marine sediments. The different glacial-interglacial cycles are called marine isotope stages and are numbered from young to old. The vertical red lines mark dated volcanic eruptions in Yellowstone.

Folds in outflow sheets of McDermitt Tuff, from the eruption that formed McDermitt Caldera in Nevada and Oregon about 16.4 million years ago.  The folding is called “rheomorphism” and occurred as the hot ash deposit flowed under its own weight shortly after it was deposited over preexisting topographic highs and lows.  The texture resembles that of rhyolit

Map of volcanic ashfall. Areas of the United States that once were covered by volcanic ash from Yellowstone's giant eruptions 2 million and 630,000 years ago, compared with ashfall from the 760,000-year-old Long Valley caldera eruptions at Mammoth Lakes, California, and the 1980 eruption of Mount St. Helens, Washington.

Steam rises above a hot pool at Agua Shuca, one of many thermal areas of the Ahuachapán geothermal field of El Salvador. A sudden hydrothermal explosion at Agua Shuca in October 1990 ejected steam and debris within a 200-m-radius, and about 25 people living adjacent to the thermal area were killed.

Excerpt from the Geological Map of the Gardiner 30’ x 60’ Quadrangle, South-Central Montana, by Berg and others (1999), focused on Devil’s Slide (colorful blue-green stripes at center of map excerpt).  Full unit description and map available online as Montana Bureau of Miles and Geology Open File No.