Natural Bridge EarthCache
A cache by BiT Message this owner
Hidden : 4/28/2008
Difficulty:
1.5 out of 5
Terrain:
3.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:



Natural Bridge


This EarthCache highlights one of the State of Kentucky's Pride and Joys, Natural Bridge. This EarthCache was developed under special permit from the Kentucky State Parks. This cache is open Daylight Hours Only and the Collection of Specimens, Either Biological, Cultural, or Mineral and Defacement of Geological Features and/or Vegetation is Strictly Prohibited. No bikes, off-road vehicles, or horses allowed. Please see these links, Natural Bridge State Resort Park Trail System and Kentucky State Nature Preserves Commission rules when considering the placement of a geocache, for additional rules and regulations while visiting the park.

Remember as always, Leave No Trace.


I rated this EarthCache's terrain based on doing a 1.5 mile round trip. However, you can lessen that degree of terrain by riding the Skylift (fees do apply). If you decide to hike the entire trek, you can park at the Hemlock Lodge Parking Lot (included as a child waypoint) at N 37° 46.657, W 083° 40.824. If you want to ride the Skylift you can park at the Skylift Parking Lot (included as a child waypoint) at N 37° 46.873, W 083° 41.398.

To hike, proceed to the rear of the lodge and take the Original Trail to the top. Be sure to plan on taking the Balanced Rock Trail down so you'll also be able to visit another EarthCache. Please see the trail map by clicking here.

Natural Bridge is a natural, not man-made, rock formation that has a natural passageway underneath. To qualify as a natural arch or bridge, the passageway should be at least 15" at the widest point, and at least 15" at the highest point. Smaller openings are called windows, lighthouses, or holes. An arch or bridge is created by differential weathering of the softer rock stratum leaving the harder rock stratum intact. The most common differential weathering is moisture freezing and expanding causing the rock to crack and fall away. Others include wind, windborne debris, rain, and wave action. A natural bridge is caused by wave action where the water is eroding, running underneath, and creating the formation.

Typical Natural Bridge and Arch Formation*



The diagram above, is a cross section, or vertical slice through the ridge at Natural Bridge. The diagram shows how the arch may have formed. The ridge in which the arch occurs is highly fractured (1). Fractures are oriented parallel to the length of the ridge where the arch occurs. Through time water in the valleys on either side of the ridge eroded deeper into the ridge, but also upwards into the ridge (2). Most of the time, creeks on either side of a ridge, do not meet at the same place at the top of the ridge. In those cases, arches don't form. But when the ridge is eroded in the same spot on either side of the ridge, an arch can form.

Formation of the arch is also related to fractures in the ridge. If you look at both sides of natural bridge you can see that the rock on the sides of the bridge is very straight. That is because the bridge occurs between two parallel fractures at the top of the ridge.

As water on either side of the ridge, eroded the slopes away, slabs of rock broke away along parallel fractures (3). It may help to imagine opening a book, binder side down and letting the pages fall away from the middle of the book. Slabs of rock fell away along the fractures in a similar way, until only the center of the ridge was left (4-6).

Ultimately, the streams on either side of the present arch eroded back to the level of the last two prominent fractures (6). At that time they began to undercut the ridge, probably forming rock shelters on either side of the ridge (7). Subsequently, erosion connected the two shelters to form an arch. Vertical erosion to the present shape of the arch closely follows bedding, so that erosion appears to have broken off slabs of crossbeds upwards.

* Kentucky Geological Survey and Steve Greb

To claim a find, please email me the answers to the questions below. Also you will need to upload a picture of yourself holding your GPSr with Natural Bridge in the background and a picture of yourself in Fat Man's Misery with your find log. So a minimum of two pictures is required. Logs that do not follow the finding requirements will be deleted.

Question 1: Is Natural Bridge a bridge or an arch?.

Question 2: While either going to the top or coming to the bottom of Natural Bridge you'll have to pass though Fat Man's Misery, how wide is the narrowest portion? Bring a tape measure.

Question 3: Estimate the length and height of the natural passageway underneath Natural Bridge.

Developed by A Platinum EarthCache Master

Additional Hints (No hints available.)



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