Mammoth Spring is part of a large underground river system. It’s called a first magnitude karst spring and it starts with rain falling in southern Missouri. It is the largest spring in Arkansas and the third-largest spring in the Ozark region behind Big Spring and Greer Spring. Mammoth Spring is the seventh-largest natural spring in the world.
The rain falls in Missouri and seeps into the water table. Then the water flows through a system of passages and cavities. These cavities make an underground river that comes back to the surface at the town of Mammoth Spring, Arkansas.
The emerging water forms a 10-acre spring pool that drains over a high stone dam. The spring generates about 10 million gallons of water per hour and the temperature is a constant 58 °F.
You can’t see the water at the Mammoth Spring because the mouth of the river is more than 70 feet below the surface of the large spring pool.
You can see part of the underground river that feeds Mammoth Spring nine miles northwest of Mammoth Spring at a collapsed cave in Grand Gulf State Park in Missouri. The remains of a portion of the cave are in a 130 ft deep chasm with a natural bridge over it. Dye tests have proven that the water flowing through the 130 ft chasm at Grand Gulf exits through the existing cave and comes out at Mammoth Spring.
The outlet pool is in Mammoth Spring State Park in north-central Arkansas. The outlet pool is only 500 ft. south of the Missouri border, and it can be seen from the highway. The spring’s large discharge volume rushes a few hundred feet down the outlet channel before merging with the Warm Fork of the Spring River to form the Spring River. The cold water from the spring is excellent for trout fishing on the Spring River.
Mammoth Spring was declared a National Natural Landmark by the Department of the Interior in June 1972.
What is a first-magnitude spring?
Springs are often classified by the volume of the water they discharge. The largest springs are called “first-magnitude”, defined as springs that discharge water at a rate of at least 740 gallons or 100 cubic feet (2.8 m2) of water per second.
What is a chasm?
A fissure or deep cleft in the earth’s surface; also known as a gorge.
What is a Karst Spring?
A main feature of karst springs is that water is rapidly transported by caverns underground, so that there is minimal filtering of the water and little separation of different sediments. Groundwater emerges at the spring within a few days from precipitation. Storms, snowmelt, and general seasonal changes in rainfall have a very noticeable and rapid effect on karst springs. The properties of karst springs make them unsuitable for drinking water. Poor filtering and high hardness means the water quality is poor.
What is a water table?
The level below ground where the ground is completely saturated with water.
By Renee Durham, Official Kids Mag