The situation described highlights the potential risk posed by a powerful earthquake in South Carolina’s Midlands, specifically concerning the Lake Murray dam. While the risk of a dam breach is deemed unlikely, experts have still planned for the worst-case scenario. Here are the key points:
- Flood Impact: A breach of the two dams at Dreher Shoals would send floodwaters south of I-20 into the Congaree Swamp, potentially affecting a 210-square-mile area. More than 150,000 people could be impacted within a few hours, as the water could travel up to 35 miles.
- Dam Construction: The original dam was deemed insufficient to withstand the area’s strongest earthquakes. As a result, a new backup dam, built to withstand a 7.3-magnitude earthquake, was completed in 2005.
- Seismic Activity: Earthquakes have occurred in the Columbia area, with the largest recorded at a magnitude of 3.5. Significant damage generally occurs only after an earthquake with a magnitude of 6 or higher, according to U.S. Geological Survey geologist Tom Pratt.
- Fault Lines: There are fault lines under Lake Murray, but none have a history of significant activity. Pratt further states that while the threat of a larger earthquake is low, it’s not entirely predictable.
The likelihood of a breach is low, but emergency management officials are prepared for any scenario that might unfold, especially if an earthquake were stronger than anticipated.
