Yellowstone's Moving Monuments
Blog by Emily Pierce, PLS, CFedS
Excerpt from Lasting Impressions, by Rhonda Rushing
Yellowstone was established by Congress as the world’s first national park on March 1, 1872, following three expeditions to the region (the Folsom-Cook-Peterson Expedition of 1869; the Washburn-Langford-Doane Expedition of 1870; and the official, government sponsored Hayden Expedition of 1871). The expeditions were seeking the truth to the numerous rumors about the area that was described as “smoking with the vapor from boiling springs; and burning with gasses . . . “ (Joe Meek, fur trapper, 1829). What the men of these expeditions saw astounded and inspired them. The unique geology of the area galvanized them to petition Congress to set the area aside as a “public pleasureing-ground” protecting from “injury or spoliation” the “timber, mineral deposits, natural curiosities or wonders within said park, and their retention in their natural condition.”
Photo from Lasting Impressions, page 142.
Yellowstone National Park protects the rarest collection of geysers, hot springs, fumaroles and mudpots on Earth. Found here are more than 10,000 hydrothermal features, including more than 300 geysers. This is the largest concentration of geysers in the world, approximately two-thirds of the world’s total. These features are concentrated in what are essentially the only undisturbed geyser basins left in the world - all others have been modified or destroyed by human development.
Yellowstone’s hydrothermal features exist here because of past and — we now know — ongoing volcanic activity. Enormous volcanic eruptions have occurred in the region because of a continental hotspot, a plume of heat and magma rising from inside the earth to a zone in its crust. The land surface bulges over this zone or “magma chamber,” causing fractures to develop in concentric-ring patterns. When these fractures reach the magma chamber, pressure is released and the volcano explodes, creating a crater or caldera.
Three times within the past 2.1 million years, the Yellowstone volcano has violently erupted. The volume of material ejected during these volcanic explosions is difficult to imagine. The last eruption, 640,000 years ago, sent a volume of ash and volcanic material into the atmosphere that is estimated to be 1,000 times the size of the 1980 Mount St. Helens explosion; this ash fell as far east and south as Louisiana. The resulting collapse of this volcanic eruption is called the Yellowstone Caldera, which is centered in central to western Yellowstone. The caldera is difficult to see because it is about 20 by 45 miles in size and has been filled in by subsequent, multiple lava flows.
BENCH MARKS IMPORTANT TO VOLCANO STUDIES
Thanks to scientific observations involving Yellowstone’s bench marks, we know that the Yellowstone hotspot volcano remains active today, with the pressure of the rising magma creating two resurgent domes, one near Le Hardy Rapids north of Yellowstone Lake and the other east of Old Faithful near Mallard Lake. In the 1970s, scientists noticed that trees on the southern end of Yellowstone Lake were dying because their trunks were becoming inundated by shifting lake waters. However, the water level at the lake’s northern outlet appeared unchanged. What was causing the lake to tilt? This observation led to detailed studies that resulted in the understanding that Yellowstone remains an active volcano.
The first thing that scientists from the University of Utah and the U.S. Geological Survey (USGS) did was relocate and resurvey the bench marks along the park’s road system. These bench marks were originally installed and the elevation measured by the U.S. Coast and Geodetic Survey in 1923.
Photo from Lasting Impressions, page 144.
The resurvey results were amazing. Between 1923 and the mid-1970s, the Yellowstone caldera in the central part of the park and just downstream of the lake’s outlet had risen almost 30 inches. Further studies, including in later years, the use of GPS satellites for precise measurement comparisons, showed that between the mid-1970s and 1984, the caldera rose another ten inches. Then the uplift halted, and between 1985 and 1995 the Yellowstone caldera dropped about eight inches. Since 1995, the caldera has generally been in a cycle of uplift. Some scientists now refer to Yellowstone as the “living, breathing” volcano.
Without the original data from the 1923 bench marks and the effort to locate those points for resurvey, this exciting story might not have been so well understood. To further guide research and strengthen the capabilities of scientists to track and respond to changes in Yellowstone’s volcanic activity, the Yellowstone Volcano Observatory (YVO)was formed in 2001. The YVO is the fifth U.S. volcano observatory (joining Hawaii, Alaska, the Cascades, and Long Valley) and is a partnership between the USGS, the University of Utah, and Yellowstone National Park.
Sources
Beth Kaeding, Bozeman, Montana. Retired as Yellowstone National Park Interpretive Planner
Additional photos by National Park Service
References:
Windows into the Earth: The Geologic Story of Yellowstone and Grand Teton National Parks by Robert B. Smith and Lee J. Stegel. 2000 Oxford University Press. 242 pp.
“Tracking Changes in Yellowstone’s Restless Volcanic System".” Yellowstone Volcano Observatory 2004. USGS Fact Sheet 100-03. [http://pubs.usgs.gov/fs/fs100-03]
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