When the Ground Opens Without Warning

You're rolling through what looks like gentle, forgiving country here in western Georgia. Low ridges covered in pine and hardwood, valleys that ease down to creek bottoms, red clay showing through wherever the soil's been cut. It's the kind of landscape that feels settled, stable, like it's been sleeping peacefully for ages. And that's partly true, but beneath your wheels lies a geology with some surprises that can wake up when you least expect it.

You're in the Piedmont Province here, riding over ancient metamorphic rocks, mostly schists and gneisses that were once buried deep in the roots of mountains that made the Rockies look like foothills. We're talking about rocks that are 300 to 500 million years old, cooked and compressed when continents collided to form Pangaea. The striped, foliated patterns in these rocks tell you they've been through the wringer, literally bent and squeezed under unimaginable pressure.

What's really interesting is what's happened since. As those ancient mountains eroded away, they left behind a thick mantle of saprolite, that's deeply weathered rock that's been rotting in place for millions of years. Sometimes it's 50, even 100 feet deep. It looks solid on top, but underneath it can be clay-rich, unstable, honeycombed with voids.

Here's the hazard nobody thinks about in Georgia: this isn't earthquake country like California, but we do get occasional seismic activity. There's a fault system running through here, and back in 2003, folks near Fort Payne, Alabama, just west of here, felt a 4.6 magnitude quake that sent cracks through foundations and knocked pictures off walls.

But the real danger is what happens after heavy rains. That thick saprolite gets saturated, loses its strength, and entire hillsides can let go. In 1994, tropical storm Alberto dumped two feet of rain in 24 hours across this region, and the Piedmont came apart. Landslides by the hundreds, some carrying houses with them, roads disappeared, whole sections of forested slopes slumped downhill like wet cake. People woke up to find their backyards 20 feet lower than they remembered.

Look at those roadcuts as you pass. See that red and orange mottled clay? That's your warning sign. Under the green carpet, this landscape is waiting for the right conditions to move.