From the parking area, a marked, 'County Sanctioned' trail will lead you to the falls overlook. This is NOT the area of this EarthCache. Approximately halfway to the falls you will have to take a 'Non-County Sanctioned' visitor worn 'Path'. This 'Path' heads to the North, through an open field, bringing you to the actual EarthCache. See the additional waypoint listings below for the coordinates to the Arch. You 'MUST' remain in the field, 'AWAY FROM THE CLIFF EDGE', 'DO NOT' go beyond any fence rails and obey all signs and postings placed within this park!!! Failure to comply with these simple rules could cause this EarthCache to be shut down.
Wikipedia defines a natural arch or natural bridge is a natural geological formation where a rock arch forms, with an opening underneath. The Natural Arch and Bridge Society defines a bridge as a subtype of arch that is primarily water formed. By contrast, the Dictionary of Geological Terms defines a natural bridge as a "natural arch that spans a valley of erosion".
This EarthCache will bring you to an example of a Natural Arch. Before you go to the site, I will explain a few of the possible contributing factors to the formation of this geologic wonder.
As the earth's climate stabilized, large glacial formations went through a process of melt off and retreat. As a result of this melt off, a substantial rise in water levels occurred worldwide. A shallow, warm salt-water sea developed and covered the central portion of North America. This global warming gave to ideal conditions for marine life to thrive and develop. Brachiopods, trilobites, crinoids, conodonts, corals, stromatoporoids and many other creatures inhabited this vast inland sea as time went on. This sea bottom was then covered with the skeletal remains (Calcium Carbonate) of these ancient marine creatures and sediment from erosion of the virtually lifeless landmasses. This sediment, under pressure, heat and time, eventually solidified and altered into limestone (a process called lithification). This limestone, because of its sedimentary basis, fractures horizontally (between layers) and also vertically. These fissures create channels of distribution for groundwater flow, which can be seen at times in water flowing from the rock faces. Groundwater is subject to freezing and expansion (ice wedging) which then contributes to even more fracturing of the rock layers themselves.
The sea bottom beneath these limestone deposits consisted of the softer, more easily eroded shale of the Maquoketa formation. This blue-gray colored Maquoketa shale derived from volcanic ash created during the formation of the Appalachian Mountains to the East. This Shale layer, being softer than the overlying Limestone, erodes quickly when exposed, creating unsupported outcroppings in the overlying Limestone. This erosion, along with gravity, plant root growth and ice wedging, aid in the expansion of joints, causing large blocks of Limestone to break away from the face of the Escarpment.
An incised/entrenched meander is described as a continuous flow of water over rock. An example would be a stream, river or creek, which erodes into the existing landscape. If the landscape topography is highly sloped, the water, moving quickly, generally erodes a fairly straight channel downstream. However, if the topography is level, the water, moving slower, will snake its way around any slight obstacle it encounters in the terrain. This leads to the water course making wide, curling loops that may double back on themselves. Below the arch is one of these curling loops still in its infancy. If uplift of the surrounding terrain is rapid, the flowing water will erode into the rocky terrain, attempting to remain at a constant elevation. In this manner, meanders become deeply carved ravines with shear-walled cliffs. The faster flowing outside edges of these loops carve away at the limestone cliffs creating cave like depression.
Subsidence is described as the motion of the Earth's surface as it shifts downward. Subsidence frequently occurs in Karst based terrains. Karst topography is a landscape shaped by the dissolution (dissolving) of layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Karst topography, due to this subterranean drainage, may display distinctive features, such as voids or caves.
When the roof that covered this cave like depression, became too thin and weak to hold together against the force of gravity, it fractured catastrophically and collapsed, leaving behind this arch. Eventually the entire arch at this location will collapse. This EarthCache was developed to bring people to this site to observe this geologic wonder before it completely disappears.
Fonferek Glen is a 74-acre park featuring a 25 foot waterfall as its centerpiece. Bower Creek, running the length of the park, can be a raging torrent and at others times, nothing but a trickle. Other features include the arch, limestone cliffs, a small cave, Maquoketa shale deposits and 30 acres which have been replanted to its native trees and prairie species. An adjacent quarry features smooth, glacially polished outcrops of Silurian Dolomite with glacial striations running in several directions. This is a geological gem of a park which I believe should be visited and enjoyed by more visitors.
Parking coordinates are listed below in the Additional Waypoints area. The buildings and home are private property so please stay to the marked ‘trail’ until you come to the Start of Path coordinates (about half way to the falls). Here you will turn North and continue to the posted/Path End - Reference point coordinates. Once at this location, look to your right (East) and observe a stone and wood rail fence. This is the barrier around the Arch. DO NOT pass beyond the fence.
Stop to view the falls either before or after completing this EarthCache. The falls and this EC are NOT in the same general area.
Email your answers to the questions, to me, using the link in my profile only. If your answers are not recieved by me, your log will be deleted. Photos are accepted and appreciated as long as the answers are not pictured. You do not have to wait for confirmation from me before logging this cache as completed. Most of all……learn……and enjoy the view.
1. List 2 possible contributors to the formation of this arch.
2. Estimate the size of the opening and the thickness of the upper portion of the Arch.
3. Using your GPSr, what is the distance from the “Path End - Reference point” to the fence rail? (educational task)
The Geocache Notification Form has been submitted to
Doug Hartman, Brown County Facility and Park Management
Department of the Wisconsin DNR.