The second largest spring in Missouri, Greer Spring flows into the Eleven Point National Scenic River, and actually doubles the size of the river! Starting at the base of a steep, shaded ravine, Greer Spring averages over 200 million gallons of water per day. The spring actually emerges from two locations a few hundred feet apart. The upper outlet exits a small cave, Greer Spring Cave, while the larger, lower outlet is a huge spring boil in the middle of the spring branch. From here, the waters flow approx 1.25 miles towards the Eleven Point, dropping at a gradient of 62 feet.
Several mills have been built at this location in the past, with the last one still standing near Hwy 19, on private property. Due to the steep nature and rugged access to the actual spring, the last mill was built up on the hill above the spring, over a half mile away. Power was conveyed from the spring to the mill using a series of cables and pulleys from the spring to the mill.
Before stalagmites and stalactites, caves are carved by forces of nature that are so powerful they can carve away solid rock. Don’t be mistaken Greer Spring is a cave system. This cave is “growing” or in its “infancy”, in terms of geological time that is. Caves are mostly formed by water at first, some staying filled with water for longer periods of time than others. And yet still others are always filled with water. With an average daily flow of 220 million gallons, Greer is Missouri’s second largest karst discharge, and produces a lot of new crushed rock each year into the river.
You are going to be focusing on two geological phenomenon’s that are currently happening here; Erosion and karst topography.
Erosion
Erosion is the process by which soil and rock are removed from the Earth's surface by natural processes such as wind or water flow, and then transported and deposited in other locations. In this particular area at GZ, Water has caused most of the Erosion here. Springs are both caused by erosion and causes of erosion.
Types of Erosion by Water:
Splash Erosion: Small soil particles are detached and sent airborne through the impact of raindrops on soil.
Sheet Erosion: Raindrops break apart the soil structure and it's moved down-slope by water that flows overland as a sheet rather than definitive channels. This occurs frequently during cloud bursts.
Rill Erosion: This process develops small, short-lived, concentrated flow paths. These paths create a sediment source and delivery system for hill-slope erosion. Areas where precipitation rates exceed soil infiltration rates are more prone to this type of erosion.
Gully Erosion: Water flows in narrow channels during or directly following heavy rains or melting snow. The gullies can erode to considerable depths.
Bank Erosion: Over time, banks of rivers and streams are naturally worn down.
Valley or Stream Erosion: Continual water flow alongside land (along a linear feature) creates this type of erosion. It extends downward, deepening a valley, and head-ward, extending the valley into the hillside. This occurs most frequently in times of flooding.
Piracy and losing streams:
Losing streams are common in regions of karst topography where the stream water may be completely captured by an underground cavern system, becoming a subterranean river.
A losing stream is the same thing as stream piracy. Stream piracy can also happen when the stream “sinks” into the ground and emerges from a different discharge point. (USGS)
A good example of this is Goodwin Hollow.
Goodwin Hollow at Missouri Highway 5 north of Lebanon in Laclede County.
Below is a map of losing streams in Missouri
Karst topography
Karst topography is a geological formation shaped by the dissolution of a layer or layers of soluble bedrock usually carbonate rock such as limestone or dolomite. Subterranean drainage may limit surface water with few to no rivers or lakes. Many karst regions display distinctive surface features, with sinkholes being the most common. However, distinctive karst surface features may be completely absent where the soluble rock is mantled, such as by glacial debris or confined by one or more superimposed non-soluble rock strata. Some karst regions include thousands of caves, although evidence of caves large enough for human exploration is not a required characteristic of karst. This creates land forms such as shafts, tunnels, caverns, and sinkholes. Groundwater seeps into and through these land forms. The result is a scenic landscape which is beautiful but fragile, and vulnerable to erosion and pollution.
Components of karst topography are:
Springs: Natural resurgence, or discharge, of groundwater from rock or soil to the surface.
Caves: Natural cavities beneath the surface of the earth, created by groundwater dissolving rock.
Sinkholes: Rounded depressions in the landscape. Sinkholes are often collapsed caves and can be quite deep, or they can be shallow holes. Sinkholes collect surface water running off the surrounding land, and the runoff goes directly into the groundwater.
Natural bridges and tunnels: Arches and tunnels are the remnants of collapsed caves, usually fairly short.
Seeps: Slow, small discharges of water from rock or soil to the surface.
Now for the important stuff….
From the posted coordinates, take an elevation reading from the trail head then hike down the .9 mile path to the Greer Spring.
Climb the rocks/path towards the left and observe the discharge near the cave. Then follow the path through and over the rocks down stream, under the bluff, along the drop-off to observe the lower discharge that surfaces in the middle of the spring branch.
QUESTION 1. Is the spring branch between the cave and the lower discharge free of debris such as rocks and logs?
QUESTION 2. Is the discharge from the cave flowing horizontally or vertically? Answer the same for the lower discharge.
The following answer may or may not be in the above description. 
QUESTION 3. What is the daily average flow and rank of the Greer Spring karst system?
Take an elevation reading near the spring branch. Once you return to the trail head on the top of the hill, answer this question....
QUESTION 4. What is the difference in elevation from the trailhead to the spring branch?
Optional Bonus: Post a photo of you somewhere near the spring branch.
Please enjoy both outlets of this beautiful spring, the old grist mill just down the road, fishing(remember no fishing in the spring branch), picnic and camping areas, and the beautiful Eleven Point River while visiting this area!
Permission granted by the USFS, Thanks Stan!!!
Sources:
- USGS, . N.p.. Web. 7 Sep 2013. <http://ga.water.usgs.gov/edu/watercyclesprings.html>
- William Stearman, geocaching name = (stearman5)
- Unklesbay, A.G., and Jerry Vineyard. Missouri Geology . 1st. 1. Columbia, Missouri: University of Missouri Columbia, 1992. 189. Print.
- Vineyard, Jerry. Gargoyle Country. 1st. 1. Missouri: watershed press, 2011. 136. Print.
Image sources: