Georgia's Fall Line

As Dr. Rood mentioned in class, the geology of Georgia differs to the north and south of the geologic Fall Line. The Fall Line is a twenty mile wide boundary which runs through Georgia from the southwest to the northeast and provides a dividing point between the Piedmont and Coastal Plain regions. During the Mesozoic era, what is now called the Fall Line was the shore of the Atlantic Ocean. 



The Piedmont region predominantly features igneous and metamorphic rocks, while the Coastal Plain region predominantly features sedimentary rocks. Most likely, the regions were created by the collision of tectonic plates around 300 million years ago, which is the same time as the creation of the Appalachian Mountains. To the north and south of the Fall Line, dominant soil types differ as well. Georgia soil north of the Fall Line is predominantly a type of clay soil, while south of the Fall Line soil is predominantly a type of sand soil (http://www.georgiaencyclopedia.org/nge/Article.jsp?id=h-721).



As you move farther north in Georgia's rivers, the water becomes less navigable due to the exposed rocks found closer to and in the Piedmont region, so several historic river-cities are found along the Fall Line. In Georgia, Columbus, Macon, Milledgeville, and Augusta were all located near the Fall Line and one of Georgia's major rivers. Other cities in the South, including Tuscaloosa, Alabama, Columbia, South Carolina, and Richmond, Virginia, are also located on the Fall Line (http://www.gly.uga.edu/railsback/GAGeology.html#FL). These cities became trading centers because they were established as far upstream as boats were able to navigate.

Mississipi Cotton Boat (Google didn't have one for the Ocmulgee River that I could find.)

While the Ocmulgee River is no longer navigable by ships, its navigability during the nineteenth century allowed Macon to serve as a major trading center during the mid-1800s. Macon boasted several large-scale manufacturing centers, including bricks and textiles, but cotton was the main commodity carried by ships on the Ocmulgee. By the later part of the nineteenth century, the decreased water volume in the Ocmulgee, due to agricultural endeavors lessening rainwater runoff, meant the river was unnavigable without heavy dredging. Soon, carriage by rail became the main form of transporting goods and Macon became major rail-hub for a short time ( http://www.georgiaencyclopedia.org/nge/Article.jsp?id=h-782). 

This is the Atlantic Cotton Mill in Macon, GA



From geologic activity to commerce, the presence of the Fall Line has helped shape Georgia's history, especially in Macon. Currently, there are plans to connect Columbus, Georgia, and Augusta with a "Fall Line Freeway." The interstate would allow for easier transportation of goods between the three cities and beyond by providing a direct route between the three. The route may one day include a connection to highways leading to Mississippi and Louisiana. Even though transporting goods by river is no longer the main form of shipping, the presence of "Fall Line Cities" and their importance in commerce shows the effects of Georgia's Fall Line.

Community Gardens and Soil Charts

The American Community Garden Association provides a broad definition of what constitutes a community garden:

“It can be urban, suburban, or rural. It can grow flowers, vegetables or community. It can be one community plot, or can be many individual plots. It can be at a school, hospital, or in a neighborhood. It can also be a series of plots dedicated to "urban agriculture" where the produce is grown for a market” (http://www.communitygarden.org/learn/).

Community Garden

Community gardens, like the one located in the Beall’s Hill Community near Mercer, allow people to increase sustainability in the area and to better relationships between people in the area (http://bealls-hill-garden.blogspot.com/2009/05/new-planting-date.html). The food produced by the community garden provides people with healthy, organic food that they may not have had access to before the garden’s existence. In addition, community gardens can provide benefits that might not be thought of at first. A community garden improves the quality of life for people in the garden, provides a catalyst for neighborhood and community development, stimulates social interaction, encourages self-reliance, beautifies neighborhoods, produces nutritious food, conserves resources, creates opportunity for recreation, exercise, therapy, and education, reduces crime, preserves green space, creates income opportunities and economic development, reduces city heat from streets and parking lots, Provides opportunities for intergenerational and cross-cultural connections (ACGA).

Before creating a community garden, potential planters might want to test the soil of location in order to assess soil composition and its fertility. A soil sample can be taken and used to determine these factors. The Munsell Soil Color Chart can be used to help determine the soil type and composition. The Munsell Chart was created by Albert H. Munsell and became the official color system for soil during the 1930s. The color for the chart is determined by the soil sample’s hue, value (lightness), and chroma (color purity). For a detailed explanation of how to use and read the Munsell Chart, you can visit http://www.soilsurvey.org/tutorial/page7.asp#b

Munsell Soil Color Chart

Munsell Color System

Unfortunately, contaminants are present in the soils of some urban areas and need to be tested before people create a community garden. One of the leading soil contaminates is lead, due to the use of lead paint, gasoline containing lead, lead-arsenate pesticides. However, the presence of soil contaminates does not mean people cannot create a community garden in the area. In areas of low lead contamination, measures can be taken to remove lead from the soil, such as adding phosphate to ground, or covering the contaminated soil with mulch. Also, people can add clean soil to the garden and plant crops which do not produce vast, deep root systems. If the soil contains high lead or other metal concentrations, gardeners can construct raised beds with the bottom separated from the contaminated soil. The raised beds can contain clean soil and be used to grow a variety of crops.  

Community Garden with Raised Beds

Mega Flood

My favorite film from the past three labs is Mega Flood. While watching the video, I was surprised by how such a vast space could be transformed by a glacial flood and was struck by the story of how geologists determined the cause of the Scablands unique features.

Map of Glacial Lake Missoula and Flood Path

For a long period of time, geologists were unable to determine how the Scablands were created and why it featured eratics, but J Harlen Bretz proposed a giant flood washed over the area and carved out its unique features. The theory garnered little support from a group of respected geologists who did not believe a catastrophic event caused the formations in a short period of time. In the end, however, Bretz’ theory about a flood was proven correct.

Joseph Pardee was in the room when Bretz pitched his idea and believed the theory might prove true, but he did not help support the theory until several years later. After years of research, Pardee identified the source of Bretz’ flood as Glacial Lake Missoula. Based on the evidence of glacial activity, Pardee claimed the lake was formed when a glacier blocked water flow. When the glacial dam busted and let water flow through, the immense rush of flood water crashed over the land and carved out the Scablands, which were over 200 miles from the water source. Pardee pointed to ripple marks on the land in order to show the flood from Lake Missoula flowed towards the Scablands. Bretz’ theory was finally accepted by the geologic community.      

Joseph Pardee

The theory of a flood causing such extensive geologic formations has been solidified by more recent work. In the video, a current researcher pointed towards a flood in Iceland during the late 1990s as having similar characteristics as ancient glacial floods. The video explained that under glaciers lies super-cooled water which is below the freezing temperature but still liquid due to immense pressure, which is something I would have never thought to be possible. Eventually, the liquid water creates fissures in the dam that lead to its collapse after a long period of time.

Overview of Scablands

Ripples Left by Flood

In addition to the information about the nature of glacial dams, researchers in the film created a scale model of Lake Missoula and the Scablands pre-flood to see if similar features were created. Even on a smaller scale, the physical forces of the flood, including underwater tornadoes, formed features strikingly similar to the ones in the Scablands.

Underwater Tornado Example

At the end of the video, one current Scabland researched explained that the cause of the formations was flooding but that the theory of one giant flood might need changing. Due to composition of certain sediment layers found in the canyon walls, researches have determined that the sediments could not have settle to the bottom of flood waters so perfectly all at one time and that many floods deposited them separately.

Before viewing the film, I never would have thought about a series of giant floods creating the earth’s landscape, but apparently it happened quite often. As geologists perform future research on the Scablands and other areas, more information about ancient floods might shed more light on the creation of earth’s geologic features. I’m just glad we don’t see floods like that today!