The Geology of Congaree National Park



(C) 2022 Stephanie A Erickson

Most National Parks in the West have been protected in order to preserve their Geology. Congaree National Park however, protects the largest remnant of old growth floodplain forest in the United States. Less than one-half of one percent, 11,000 acres are protected by the park. The majority of the forests were cut for ships, railroads and buildings. The floodplains were drained for pastures, farms and cities. Congaree is a low bottomland forest in the coastal plain of South Carolina. The coastal plain once extended from the foothills of the Appalachians from the Chesapeake Bay to Eastern Texas. The rivers in this area are slow moving and flood the plain several times a year creating a nutrient rich muck. William Faulkner described these forests as:


“The thick black slow, unsunned streams, almost without current, which once each year ceased to flow at all, and then reversed, spreading, drowning the rich land, and subsiding again, leaving it still richer”.

The Santee River Cypress Logging Company began to operate in the area of what is now the park in 1898. The logging company owned by Francis Beidler and Benjamin F. Ferguson of Chicago; the company operated until 1914. Harry Hampton was an environmental journalist for the State in the 1950’s and 1960’s was integral in protecting the Swamp. In 1959, he brought a group of National Parks Service officials to the Congaree Forest and the Nature Conservancy. The National Parks Service began a review of the advocacy efforts made by Hampton and others. In 1963, the National Parks Service recommended the conservation of the Congaree “swamp”. In the early 70’s the Biedlers began selling off logging rights, this galvanized the grass roots efforts of the Environmental Coalition, The Audubon Society, and Sierra Club to increase efforts for preservation. They began to look for National support and in 1975, South Carolina Senators Strom Thurmond and Ernest F. Hollings introduced legislation for the establishment of a national preserve, the legislation was passed to create Congaree Swamp National Monument. In 2003, it became a National Park under George W. Bush, and its boundaries were increased by 4,576 acres. Congaree is the 10th least visited Park in the contiguous United States system with approximately 150,000 +/- visitors each year. The boardwalk trail is completely stroller and ADA accessible making 2.4 miles of trail accessible to all visitors.


Congaree is now protected as a United Nations Educational, Scientific, and Cultural Organization (UNESCO) International Biosphere Reserve because of the amount of biodiversity. A biosphere reserve is a representative ecosystem that preserves the genetic diversity of species by protecting wild animals, traditional lifestyle of inhabitant and domesticated plant/animal genetic resources. In other words, Congaree is Internationally protected due to its biodiversity. In addition, 15,269 acres of Congaree National Park are protected as federally designated wilderness. The southern boundary of the boardwalk trail parallels the Wilderness Boundary. The Weston Lake Trail, Oak Ridge Trail, Kingsnake Trail, River Trail, and Oakridge Trail are all located within the protected wilderness boundary.


Figure 1 - National Parks Service Map of Congaree National Park

Congaree has the largest number of champion trees and champion sized trees (15 different species) in the United States. Champion trees are the largest, tallest, or most significant of their kind in the state or in the nation. Champion trees in Congaree are primarily located within the Federal Wilderness designated areas and include a 167-foot loblolly pine, a 157-foot sweetgum, a 154-foot Cherry bark oak, a 135-foot American elm, a 133-foot swamp chestnut oak, a 131-foot over cup oak, and a 127-foot common persimmon.


Congaree has over 80 different species of trees, several of those species are champion trees such as the paw-paw, loblolly pine and sweetgum. One species, the bald cypress, is an extremely interesting species. Old growth bald cypress trees were once found across the continental United States. Cypress were logged heavily between the 1880’s through the 1940’s leaving only a few sections of the bald cypress untouched. In fact, the floor of my parents' living room is cypress and when we have to move my mom from the home, that floor is coming out and being saved. Cypress are deciduous conifers. So, they have needles and cones like a conifer but drop them in the fall like a deciduous tree does. The Cypress is a cousin of several other iconic National Park trees, the Sequoias of Yosemite and the Redwoods of Muir Woods. All three belong to the same species family. While the Bald Cypress does not grow as tall as its western cousins, they can be just as old, some of the cypress trees in the park are over 500 years old.


There are several other endangered species in the park, the red-cockaded woodpecker (Dendrocopus borealis), American alligator (Alligator mississippiensis) and bald eagle (Haliaetus leucocephalus). (UNESCO, 2022) We heard the woodpecker but could not locate it in the tree canopy and saw a small American alligator floating in Weston Pond, but we did not see the bald eagles during our visit. Congaree is an ornithologist's dream. In fact, we spoke with several wildlife photographers during our day in the park. It sounded like we were walking through Jurassic Park with a symphony of bird calls and small animal calls in the park. We observed several cardinals, hummingbirds and a prothonotary (pro-tho-no-tary) warbler on our hike and heard the barred owls in the southwestern section of the boardwalk. One section of the boardwalk was closed due to tree and flood damage.



Prothonotary Warbler @2022 Stephanie A. Erickson


Prothonotary Warbler (c) 2022 Stephanie A. Erickson

The geology of the park is rather unique compared to our previously visited parks in the west. There was very little elevation change. In fact, across the 15 miles of the park, the topographic elevation only changes 20 feet. Due to this minor change in elevation, Congaree is prone to multiple flooding events per year. During these events approximately 90% of the Park floods. There was no surficial bedrock so the geology I will talk about will be primarily surficial geology and the topographic features of the park. These geologic features have helped to shape the park and have been integral in the creation of the biosphere reserve. The topography of the park has been shaped by numerous processes. Two migrating rivers, sea level changes, faults and the growth of the forest itself.


Most of the surficial geology in the park formed in near coastal to coastal areas, and the shallowest portions of the continental shelf. Sea level in this area changed multiple times due to tectonic events that occurred during the Pliocene, Pleistocene, and Holocene. Fossilized grass pollen samples from sediments that date to the Pilocene and Pleistocene indicate that Congaree was a cooler and drier Savannah-like environment. It was during this time that the river valleys terraces began to form. A river valley terrace forms when a river flows at a higher elevation in the past and erodes its banks and creates these flat plateaus with distinct edges.


The Augusta Fault lies beneath the Congaree River. Back in the Triassic period, when the supercontinent of Pangea was breaking apart, this area of central South Carolina experiences extensional forces which created rift valleys which filled with sediment eroded from the Piedmont and Blue Ridge provinces. After about 150,000 years give or take, the extensional forces subsided, and sea levels rose in the area. This caused marine sediments to be deposited in the area. According to the South Carolina geological map, the area of Congaree National Park is underlain by the Congaree Formation, a clastic sandy formation that contains sharks' teeth and mollusks. (South Carolina Geological Survey, 2014).


During the Antarctic glaciation period in the Oligocene, sea levels fell again in this area. Sea levels rose during the Pliocene and the nearshore environment was only a few miles from Congaree National Park. (USGS, 2022) Spruce pollen has been identified in the sediments in the park. During our last glaciation, 21,000 years ago, the park's climate would have been similar to current day southern Canada in order to produce these spruce trees.


There are several oxbow lakes within the confines of the park. An oxbow lake is formed when a meander on a river is cut off when the river changes direction. Weston Lake is the largest of the oxbow lakes in Congaree and is unique to the lakes in the park because it has a gravel rather than clay base. A small American Alligator floating in the middle of the lake during our visit.


Weston Lake (c) 2022 Stephanie A. Erickson


Due to the lack of topography within most of the park, this allows the park to be prone to flooding events. The flooding events however bring a lot of needed nutrients to the biodiversity of the park. The old growth trees have intricate and deep root systems that restrict water in the floodplain and this influences the deposition of sediment and nutrients. Geologists and biologists use Congaree to study the influence the forest has on the landscape after storm and climate events.


Congaree has several rim swamps within the confines of the park. A rim swamp is an area where the groundwater collects at the surface. Some of the most diverse plants in the park can be found in the rim swamps including the endangered Carolina bog mint. The Muck Swamp located near the visitor's center is the only swamp in the park that contains muck and peat deposits.


Rimswamp (c) 2022 Stephanie A. Erickson


As I mentioned previously, walking through the park sounded like we were walking through Jurassic Park. The cacophony of bird calls was amazing. I need to return and record and then pipe it into my classroom. I couldn't even use my Song Sleuth app because there were too many calls going on! If you aren't familiar with the app Song Sleuth is an app created by Wildlife Acoustics in collaboration with bird expert and illustrator David Sibley. The app is perfect for all two-bit ornithologists, to quote Sheldon Cooper. One of the other apps I use when investigating new environments is iNaturalist. iNaturalist allows you to snap a photo of a species and identify the species. Insects, plants, fungi, and any biotic species can be identified using this app. It also geolocates the image so you can crowdsource biodiversity data.


That's all for Congaree National Park. Tune in to my next episode as I take you on a geologic tour of another one of the least visited National Parks, The Channel Islands National Park.


Until next time.


Vocabulary

Champion tree - a designation afforded to selected trees that are special or superlative because of their height, size or significance


Biosphere reserve- multipurpose protected areas with boundaries described by legislation. The main aim of biosphere reserve is to preserve genetic diversity in representative ecosystems by protecting wild animals, traditional lifestyle of inhabitant and domesticated plant/animal genetic resources.


Conifer/ coniferous - softwood trees identified by their needle like leaves and seed producing cones.

Rift valleys - linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics.


Oxbow lake - lake formed when a bend in the river is cut off


Rim swamp - an area where the groundwater collects at the surface, often where the highest amount of biodiversity is found.