Hot Springs National Park (HOSP) lies within and adjacent to the city of Hot Springs (population about 33,000) in central Arkansas (fig. 1, fig. 2). HOSP has an area of about 5,450 acres (Stephen Rudd, National Park Service, oral commun., 2000). The Park is in a physiographic area known as the Ouachita Mountains, an area typified by intensely folded and faulted shales and sandstones that produce many east-west trending mountain ridges (Fenneman, 1938). HOSP was set aside as a federal reservation in 1832, and was established as a National Park in 1921. Several hot springs are the primary natural resource of HOSP, but unlike thermal features in other national parks such as Yellowstone National Park, they have not been preserved in their unaltered state. Instead, the springs have been managed to conserve the production of uncontaminated hot water for public use (National Park Service, 1986). From the early years of the reservation, pipes, flumes, and tanks were developed to collect, cool, and transport water from the springs. A thermal water distribution system (described more fully and diagrammed in National Park Service, 1986) consisting of covered concrete basins around the orifices of most of the hot springs and collection and distribution lines has been in place for many years. A group of bathhouses, built between 1892 and 1923 and currently known as the Historic Landmark District of Bathhouse Row, is the primary cultural resource of the park. This group of bathhouses is one of the few collections of historic bathhouses remaining in the United States (National Park Service, 1997). Bathhouse Row lies along the east side of Central Avenue (Arkansas Highway 7) and immediately west or southwest of the hot springs.
The rocks cropping out in the vicinity of the hot springs at HOSP are sedimentary rocks, although intruded igneous rocks are exposed in the region (Purdue and Miser, 1923; Bedinger and others, 1979). The sedimentary rocks are relatively old (Paleozoic) and consist of shale, chert, novaculite, and sandstone. The most areally extensive formations with outcrops near HOSP are the Stanley Shale, Hot Springs Sandstone Member of the Stanley Shale, Arkansas Novaculite, and Bigfork Chert (fig. 3). The beds of sedimentary rocks generally are steeply inclined because of mountain building forces in late Paleozoic time. The flow system that yields thermal water to the hot springs of HOSP is not fully understood. Bedinger and others (1979) present data and conceptual and mathematical models based on geologic and geochemical data that describe the hot-springs flow system (fig. 4). They provide evidence that almost all of the hot-springs water is of local, meteoric (i.e., atmospheric) origin from recharge of the Bigfork Chert and the Arkansas Novaculite. They suggest that the water slowly percolates to depth, resides in the heated part of the system for a relatively short time (no more than a few hundred years), and then travels rapidly to the surface. Based on carbon-14 dating, Bedinger and others (1979) estimate that the age of much of the water exceeds 4,000 years. The hot springs emerge along a line about 1,500 feet long, from the plunging crestline of a large overturned anticline (a fold of rock with the stratigraphically older rock at its core) along the southern margins of the Ouachita anticlinorium in the Zigzag Mountains (Bedinger and others, 1979). The springs emerge from the Hot Springs Sandstone Member of the Stanley Shale. Some geophysical and geological data suggest a somewhat different scenario (Bergfelder, 1976) -that the hot springs are located above the western edge of a large pluton (an igneous intrusion) with an upper surface about 4,000 feet below land surface that extends eastward from an igneous outcrop near Magnet Cove (fig. 1). Bergfelder suggests that the meteoric water percolates through a fracture zone (location unspecified) associated with the margin of the pluton and then (because the heat source is unknown) either takes in heat from the pluton, percolates below the pluton to depths of about 8,000 to 12,500 feet and takes in heat, or percolates below the pluton to a lesser depth and takes in heat from underlying magma. The Bigfork Chert and the Arkansas Novaculite outcrop areas, which may serve as recharge areas, primarily lie north and northeast of the hot springs (Bedinger and others, 1979). Outcrop area of the Bigfork Chert is about 36 square miles; outcrop area of the Arkansas Novaculite is about 13 square miles. Many of the cold springs in the area issue from the Bigfork Chert at contacts of the Bigfork Chert with less permeable formations (Bedinger and others, 1979). This association was noted by Purdue and Miser (1923). More detailed descriptions of the geology are found in Purdue and Miser (1923), Arndt and Stroud (1953), Bedinger and others (1974), Bedinger and others (1979), and Bedinger (1994).
Bedinger, M.S., Pearson, F.J., Jr., Reed, J.E., Sniegocki, R.T., and Stone, G.G., 1974, The waters of Hot Springs National Park, Arkansas-their origin, nature and management: U.S. Geological Survey open-file report, 102 p.
Bedinger, M.S., Pearson, F.J., Jr., Reed, J.E., Sniegocki, R.T., and Stone, G.G., 1979, The waters of Hot Springs National Park, Arkansas-their nature and origin: U.S. Geological Survey Professional Paper 1044-C, 33 p.
Fenneman , N.M. , 1938, Physiography of eastern United States : McGraw-Hill , New York . 690 p.
National Park Service, 1986, General management plan /development concept plan, Hot Springs National Park : National Park Service, 105 p.
National Park Service, 1997, Resources management plan: Hot Springs National Park: National Park Service, 48 p.
Purdue and Miser, 1923, Description of the Hot Springs District [ Arkansas ]: U.S. Geological Survey Atlas, Folio 215.
That's what attracts people to Hot Springs. In fact they have been coming here since the first person stumbled across these hot springs perhaps 10,000 years ago. Stone artifacts found in the park give evidence that lndians knew about and used the hot springs. For them the area was a neutral ground where different tribes came to hunt, trade, and bathe in peace. Surely they drank the spring waters, too, for they found the waters, with its minerals and gases to have a pleasant taste and smell. These traces of minerals, combined with a temperature of 143�F, are credited with giving the waters whatever therapeutic properties they may have. Waters from the cold springs, which have different chemical components and properties, are also used for drinking. Besides determining the chemical composition and origins of the waters, scientists have determined that the waters gushing from hot springs are more than 4,000 years old. And the waters gush at an average rate of 850,000 gallons a day.
What's Special about this Water
The most important thing about Hot Springs' thermal water is that it is naturally sterile. For this reason the National Aeronautics and Space Administration (NASA) chose this water, among, others, in which to hold moon rocks while looking for signs of life. Even during the many early years that the springs were uncovered, the absence of bacteria in the water helped prevent the spread of disease. Today most of the springs have been covered to prevent contamination. Various open springs and a spring cascade on the Arlington Lawn give an idea of what the area would be like if all the springs were open with the water pouring down the hillside into the creek.
What Makes this Water Hot ?
In an arc from the northwest around to the east, outcroppings of Bigfork Chert and Arkansas Novaculite absorb rainfall. The pores and fractures in the rock conduct the water deep into the Earth. As the water percolates downward, the increasingly warmer rock heats it, and filters out the impurities. In the process the water dissolves minerals in the rocks. Eventually the water meets the faults and joints in the Hot Springs Sandstone leading up to the lower west side of Hot Springs Mountain where it flows to the surface.
The General park map handed out at the visitor center is available on the park's map webpage.For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.
A geology photo album has not been prepared for this park.For information on other photo collections featuring National Park geology, please see the Image Sources page.
Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.
Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
9" x 10.75", paperback, 550 pages, full color throughout
The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!
Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.
For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.
The NPS maintains a searchable data base of research needs that have been identified by parks.
A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.
NPS Geology and Soils PartnersAssociation of American State Geologists
Geological Society of America
Natural Resource Conservation Service - Soils
U.S. Geological Survey
Currently, we do not have a listing for any park-specific geology education programs or activities.
General information about the park's education and intrepretive programs is available on the park's education webpage.For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.