Grand Bay a Carolina Bay Earthcache EarthCache

Carolina bays are elliptical depressions concentrated along the Atlantic seaboard within coastal Delaware, Maryland, New Jersey, North Carolina, South Carolina, Virginia, Georgia, and north central Florida. However, the largest concentrations are found in North and South Carolina, thus the name Carolina Bays. The Bay reference is for the bay trees frequently found in them, not because of the frequent ponding of water (Sharitz 2003).

Other landform depressions, not widely accepted as Carolina bays, are found within the northern Gulf of Mexico coastal plain in southeast Mississippi and Alabama, where they are known as either Grady ponds or Citronelle ponds. Carolina bays vary in size from one to several thousand acres. About 500,000 of them are present in the classic area of the Atlantic Coastal Plain, often in groups, with each bay invariably aligned in a northwest-southeast direction. The bays have many different vegetative structures, based on the depression depth, size, hydrology, and subsurface. Many are marshy; a few of the larger ones are (or were before drainage) lakes. Some bays are predominantly open water with large scattered pond cypress, while others are composed of thick, shrubby areas referred to as pocosins, with vegetation growing on floating peat mats. Generally the southeastern end has a higher rim composed of white sand. They are named for the bay trees frequently found in them, not because of the frequent ponding of water (Sharitz 2003).

Origin of Carolina Bays

Theories of the origin of the Carolina bays fall into two major categories: that these features were created by forces within the Earth (geomorphology), or that they were gouged by an astronomical event or set of events (impact events).

Geomorphology

Various geomorphological theories have been proposed to account for the bays, including action of sea currents when the area was under the ocean or the upwelling of ground water at a later time. One major theory within the earth sciences academic community is that a combination of processes created the shapes and orientations of these ancient landforms, including climate change, the formation of siliciclastic karst by solution of subsurface material during glacial sealevel lowstands and later modification of these depressions by periodic eolian and lacustrine processes.

Quaternary geologists and geomorphologists argue that the peculiar features of Carolina bays can be readily explained by known terrestrial processes and repeated modification by eolian and lacustrine processes of them over the past 70,000 to 100,000 years. Also, quaternary geologists and geomorphologists believe to have found a correspondence in time between when the active modification of the rims of Carolina bays most commonly occurred and when adjacent sand dunes were active during the Wisconsin glaciation between 15,000 and 40,000 years and 70,000 to 80,000 years BP. In addition, quaternary geologists and geomorphologists have repeatedly found that the orientations of the Carolina bays are consistent with the wind patterns which existed during the Wisconsin glaciation as reconstructed from Pleistocene parabolic dunes, a time when the shape of the Carolina bays was being modified.

Impact event

The cometary impact theory of the origin of the bays was popular among earth scientists of the 1940s and 50s. After considerable debate and research, geologists determined the depressions were too shallow to be and lacked evidence of impact features. Reports of magnetic anomalies turned out not to show consistency across the sites. There were no meteorite fragments, shatter cones or planar deformation features. None of the necessary evidence for hyperspeed impacts was found. The conclusion was to reject the theory that the Carolina bays were created by impacts of asteroids or comets.

A new type of extraterrestrial impact hypothesis was proposed as the result of interest by both popular writers and professional geologists in the possibility of a terminal Pleistocene extraterrestrial impact, including the Younger Dryas Impact hypothesis. It said that the Carolina Bays were created by a low density comet exploding above or impacting on the Laurentide ice sheet about 12,900 years ago. However, this theory has been discredited by optically stimulated luminescence (OSL) dating of the rims of the Carolina bays, paleoenvironmental records obtained from cores of Carolina bay sediments, and other research that shows that many of them are as old as, or older than, 60,000 to 140,000 years old.

Carolina Bays Soils

Carolina Bays have characteristic soil assemblages which are the result of the very moist conditions commonly found in these environments and which can be distinguished easily from one another and from surrounding soil types on aerial photographs. Wet soil generally appears darker due to the greater accumulations of black organic matter. However, when winter cover crops have been planted, wetter soils usually support more vigorous plant growth and appear a deeper red or pink on infrared photographs than drier soils. Soil mapping surveys, such as those run by the United States Department of Agriculture, commonly draw boundary lines, delineating different soil types, directly on aerial photographs while working in the field. These surveys look at factors such as landscape position, shades of bare soil, types of vegetation growing on the soil, and water drainage patterns commonly found on that soil. Although not all soils can be so easily determined, the unique soils of the Carolina Bays can usually be separated and identified on a variety of remotely sensed images.

Three distinct soil types are found in most of the larger Carolina Bays.

- PONZER - This is often the dominant soil in large Bays, and it is also found in the center of smaller ones. Due to the lack of oxygen caused by water saturation, which slows decomposition, this soil is almost all organic matter. The soil microbes which would normally cause complete decomposition need oxygen to break down the leaves and other plant litter that fall to the soil surface. Over the years, an organic rich "A" horizon layer accumulated that is several feet thick. This soil appears dark in an aerial photo. While some pine trees can grow in it, they cannot compete well with better adapted deciduous vegetation. When drained, this is a highly productive agricultural soil.

- RUTLEDGE - This soil is found along the inside of the boundary of large Bays and occupies most or all of the area of smaller Bays. It is slightly higher in elevation than Ponzer soils and is therefore slightly drier. It also has high organic matter content but is much sandier. It also more easily supports loblolly pine trees. Rutledge soils also make productive agricultural land when drained. The land appears dark in an aerial photo, but not as dark as Ponzer. In Infrared aerial photos (taken in winter), Rutledge soils will appear much redder than Ponzer due to the abundance of evergreen trees such as pines.

- RIMINI - This soil is sometimes found on the sandy rims of Carolina Bays. It is a rather unusual soil in that its subsurface "B" horizon layer is full of organic acids combined with aluminum atoms that leached from overlying horizons. While the surface color can be bright enough to appear almost white, the color of the "B" horizon layer is often brown or black, like topsoil, but it is found about four feet below the soil surface. [Soils of this type are usually found in northern regions, like New England, Northern Michigan, Minnesota, and Canada.] For several reasons, including acidity and possible aluminum toxicity, this is not a good soil for plant growth and is only sparsely covered by scrubby pines, blackjack oak, and turkey oak. This is not an extensive soil, and is almost never used for agriculture. It appears very light in an aerial photo due to the high sand content and dryness of the soil surface.

Typical Carolina Bay Soil Types

Carolina Bays as a Unique Natural Habitat

Carolina Bays are the dominant freshwater wetland feature of the Coastal Plain of South Carolina. But not all Bays provide the exact same habitat conditions. Some Bays are wet all of the time, supplied by springs, producing a bog-like ecosystem with its associated unique mix of plant and animal species. These Bays maintain an acidic environment with very low oxygen levels. Various species of blueberries, wild azaleas, hollies, loblolly bays, pond pines, and abundant vines and briers thrive in those unique habitat characteristics. Some wet Bays also contain rare insectivorous plants such as the Venus fly trap, pitcher plant, and sundew. In turn, this lush vegetation has attracted various species of wildlife, ranging from the small tiger salamanders and tree frogs, to much larger bobcats and alligators. The thick underbrush also offers a safe haven to deer. Other Bays are dry much of the time providing a more grassy savanna-like habitat. Rare plant species are also found in drier Bays. Examples include mock bishop's weed, quill-leaf, rose coreopsis, and spoonflower.

Sand rims

Sand rims are one of the trademarks of the Carolina Bays, but far less attention has been devoted to the nature of their origin than to that of the elliptical basins and their orientations. It is likely that the Bays contained open water at some point in their development, probably during the Pleistocene moist phase. Since modern southeastern winters occasionally bring freezing temperatures and since glacial Pleistocene winters were colder than winters today, it is likely that the Pleistocene Bay Lakes froze partially or completely each year. Collision of wind-driven ice with the sandy shore combined with thermal expansion of ice on completely frozen lakes could have left substantial ice-push ridges around the perimeters of the lakes with the strongest development on the down-wind shores; in fact, sand rims around Carolina Bays are best developed on the southeast, or downwind, sides of the basins. The formation of ice-push ridges has been well documented for lakes at higher latitudes, including those with rocky and gravel-strewn shorelines that would be more resistant to ice action than loose sands. Concentric and intersecting sand rims in some Carolina Bays may therefore reflect transgressions or oscillations in lake levels.

Grand Bay WMA

The larger Grand Bay ecosystem contains four Carolina Bays and is part of the Banks Lake ecosystem. The size of the Grand Bay ecosystem is second in Georgia only to the Okefenokee Swamp, the largest wetland in the state and one of the largest in the Southeast. Like the Okefenokee, Grand Bay offers many plant communities, including upland longleaf and slash pine flatwoods, cypress and gum swamps, savannahs, and various shrub bogs.

Interpretive experiences include access to the wetland along a half-mile boardwalk, which ends at the Kinderlou Tower, a gift of local businessman Harley Langdale Jr. This structure, once a fire tower that overlooked Langdale Forest Products' timberland, has been modified to allow observation of Grand Bay's plant and animal life. The boardwalk takes the visitor through many features of the wetland, such as a wet savannah, shrub bogs, a black gum/cypress pond, and a prairie with various herbaceous plant communities.

You Do Not Have to Climb the Tower to Complete this EarthCache!

Dogs are not allowed on the boardwalk due to being an alligator attractant. Leave your pet(s) at home!!

Grand Bay, as of Jan. 01, 2012, is now a User Fee Area. You must possess one of the following to enter. 3-day hunting/fishing license; sportsman, lifetime or honorary license; wildlife management area license; Georgia outdoor recreation pass (GORP). Permits may be purchased at georgiawildlife.com or by calling 1-800-366-2661.

To log the cache and get the smiley, send me an email with the answers to the following questions:

1 – Using the information above, would you consider the soil type to be Ponzey or Rutledge at the end of the boardwalk and why?

2 – What is the size of this geologic formation? Please use the information found on the sign at the posted coordinates to determine this answer. Other information sources (internet for example) differ slightly from the information posted on site.

3 – Given the information above, would you consider Grand Bay open water, pocosin, or a combination of both and why?

4 - Optional - A photo of you and your GPSr somewhere along the boardwalk would be appreciated (but not required). If you have the ability to take and upload a photo, please do so. Also, upload a picture or two of some of the wildlife you may have encountered along your walk.

Logs that do not have answers emailed within 24 hours will be deleted without notification.

If you would like to read more scientific information on Carolina Bays in Georgia, check out this 2002 report and survey. For the more casual side, check out this link.

References
Wikipedia, Carolina Bays
The Age and Trophic History of Lake Waccamaw, North Carolina - J. C. STAGER and L. B. CAHOON
University of South Carolina – Section 8 Coastal Plain Region/Carolina Bays