Landforms in Northern Alabama


Karst Topography, joints, and differential erosion I

NOTE: do not use acid (even the mild stuff we have) nor the rock hammer without EYE PROTECTION!!

Stop 1. The ‘Rockpile recreation area’.

As you walk along the bluffs note the layering (horizontal joints) in the sedimentary rocks. What do these differences tell you about the depositional environment? Are there significant differences in weathering and erosion between different layers? Select a sample of limestone and a chert nodule, apply the ‘acid test’. Describe the different reaction. What is the origin of Chert? Describe how the outcropping of the Ft. Payne formation effected human settlement and development of this area.

Note the vertical cracks; these are joints that fracture across the layers of sedimentary rocks.

Create a sketch indicating both horizontal and vertical features


Use a compass to determine the compass bearing of the water flowing out of each stream channel (go ahead and get wet). Is the direction similar for each stream? Is the direction of the joint structure in the rock expressed by the apparent course of these streams?

Look on the map, are there any surface streams present that would explain the waterfall, or sub-surface streams?

Plot a line with the apparent compass bearing of the joint structure on the topo map; identify potential sources of water for these streams. Discuss the long term stability of

Wilson Dam.

Creating a Linear Transect. A useful way of acquiring a valid sample for a landscape is a linear transect. Sometimes, a linear transect is also known as a “windshield survey”.

For the transect portion of this lab, begin at the intersection of 2 nd

street and Gnat Pond

Road. Make sure there are at least 2 of you in the car, one to drive and call off the mileage and a second to record your observations. At every mile, record the vegetation on both sides of the road and a descriptive term for the topography (flat, steep, swampy, etc). In your write up, include a chart of vegetation and topography(referenced to the base map). Indicate where significant changes take place.

Stop 3. LaGrange College Site:

Describe the dominant vegetation, how is this different from the vegetation visible below the ‘mountain’? In terms of altitude… just how tall is this mountain? (it is only a few parts of the world where a feature of this size would deserve the term ‘mountain’!!).

Stop 4. End of the pavement…What is the primary rock of this ‘mountain?’… What inferences can you make about the erosion potential of this rock as opposed to the limestone of our previous trips? What causes the different colors found in this sandstone?

Using your observations from this trip, discuss the impact of differential erosion on the makeup of the landscape.

Stop 5.The LaGrange cemetery…quoting from

The town of LaGrange is now referred to as the "city of the dead," because its cemetery is the only thing that is intact. This beautiful and mysterious cemetery is one of the only clues remaining from the Civil War that can inform us about the families who lived on the mountain. There are currently 150 graves which are known to The LaGrange Living Historical Association. But it is estimated that there are at least 200 graves in the cemetery. The Association is making an effort to put names and locations on the 50 or so unmarked graves in the cemetery.

“The cemetery holds many names and legends, as well as some interesting stories. It has fallen victim to the times, however, and has suffered greatly from vandalism. There used to be stone crypts covering most of the graves, but now there are only a few intact. A rose bush that had been growing in the cemetery for over 160 years was removed by an unknown visitor. The LaGrange Historical Association has attempted to preserve this historic site and has managed to raise enough in donations to put a fence up around the area, in an effort to deter vandals.”

Visit the historical web site

which describes the beginnings of UNA. In your analysis relate the cultural history of this place to the physical geography/geology that make this place unique.

In 1818-1819 one hundred and fifty people purchased land on the spur of the

Cumberland mountain, 400 feet above the surrounding valley. The earliest settlers, who were the wealthiest people in the valley, used the land as a summer resort which they called "Rocky Hill." As the settlement became more permanent, the people demanded a place to educate their sons and daughters. The Methodist church stepped in, and donations were collected to build a church for worship and schools for education. They called it "LaGrange" meaning "the place," for the view from the area was breathtaking.