Nov/Dec 2013Earth and Water, Wind and Sun
Digging into the Past – Planning for the Futureby David Lucas
In 1825, long before the existence of fish and game regulations or other organized wildlife management efforts, the state legislature directed Columbia geologist Lardner Vanuxem to undertake a "Geological and Mineralogical Survey" of South Carolina. Vanuxem concentrated on cataloging the minerals found in the piedmont, and his reports were widely published, with the goal of encouraging development of the state's mineral resources. That standard of open information sharing continues today in the work being done by the S.C. Geological Survey. All information collected is made available to private-sector businesses, local governments and the general public. Providing that information - "Information is data in context," Clendenin likes to say - is a big part of the mission.
Statewide geologic maps, quadrangle scale maps, and print-on-demand publications are available via the section's website at www.dnr.sc.gov/geology, as well as downloads of the digital data that support these materials. A talented and computer-savvy technology staff plays a fundamental role in the section's work by using the latest software to organize information collected through field work into useful formats. The inventory of geological and mineral information managed by the section also includes the State Core Repository, a collection of core samples collected during drilling operations like the one at Creston. This treasure trove of information about the natural resources beneath the surface of the Palmetto State is an important resource for scientists, consultants and other decision-makers.
"We just try to fill that niche of providing accurate earth sciences information," says Chief Geologist Scott Howard. "We are developing original geologic information that will help people - whether in government or the private-sector - make good, science-based decisions."
While outreach and education, data management, and technical assistance all play a role in fulfilling the Geological Survey's mission, just like in Vanuxem's day, geologic mapping is the foundation. In the end, (or the beginning, actually) creating a detailed and useful body of knowledge about geological resources entails painstaking fieldwork. Since 1993, the Geological Survey has received funding to map geologic resources across South Carolina through a federal cost-share program called "STATEMAP." The program builds upon earlier mapping efforts and will eventually include geologic maps of the entire state in sixty-four-square-mile "quadrangles."
How do you get reliable information about what's happening below the surface? Well, in the coastal plain of South Carolina, where the STATEMAP project's current efforts are centered, you drill holes in the ground - lots and lots of carefully measured holes at precise, GPS-measured coordinates. An average of one hole for every two square miles is needed to create a reliable map, says DNR Regional Geologist Will Doar.
Doar and his crew use a technique called "shallow augering" to map the subsurface geology of a given quadrangle. The depth of a particular hole depends entirely on the local geology - how far down does the relatively soft top layer go before you reach the harder layers underneath? The depth of that upper layer varies, depending on the terrain, but in the South Carolina Lowcountry, it's fairly "young" - at least in geologic terms.
"In the Lowcountry, what we are most concerned with is the last 2.5 million years of geologic history," says Doar. "What we are mapping now could give us some hints about what will happen with beaches and floodplains if sea level rises significantly again."
Geologic mapping is also valuable for land-use planning and environmental protection. Many Lowcountry areas are experiencing skyrocketing population growth, and reliable geological information is critical for local decision-makers struggling with managing that growth. "Helping local government planners make intelligent choices about future growth has been a really important benefit of this work," says Doar.
SET – Measuring the Impact of Sea Level Rise
SET stands for Sediment Elevation Table, which is both a S.C. Geological Survey project and the instrument used in the project. SETs are being monitored at specific locations in the salt marshes along the South Carolina coast.
Each SET station consists of metal rods driven far enough into the ground that their positions are fixed in space. That position is then precisely measured to within 2.5 cm. The SET instrument very precisely measures the surface elevation of the marsh surface (to within 4 mm). Over time, these measurements can track changes in the marsh elevation, which could be caused by the marsh surface changing (growing or receding), deeper subsurface elevation changes (subsidence or uplift), or both.
Why do DNR scientists care whether the land beneath Lowcountry salt marshes is rising or falling? It's simple. We now know for certain that sea level is rising along the South Carolina coast, and the marshes that line the edges of Port Royal and St. Helena sounds, Bulls and Winyah bays, and other coastal zones are nurseries for thousands of different types of marine organisms - including some of our most popular recreational and commercial species such as shrimp and red drum. The important question is: as sea levels rise over the long-term, will these areas become inundated and more bay-like, or will the ground underneath the marshes rise as well - maintaining a rough equilibrium. The answer to this question has huge implications for the future well-being of the state's marine fisheries, and DNR geologists are working hard to find it.