By “Biff” and Susan Andrews

Geology may not be exciting, but it sure can be interesting.

Consider Smithfield and Suffolk. What lovely settings! High land above productive salt marshes, fertile land — no wonder the Warroscoyacks and Nansemond tribes settled here in Western Tidewater.

But there is no “Western Tidewater.” There’s only “West OF Tidewater.” Suffolk and Smithfield are west of it. So where does Tidewater stop? A good question for a naturalist.

If you visit the oceanfront — either here or in North Carolina — you’ll notice a line of sand dunes about 25 feet high bordering the ocean. That’s the present.

But in the Pleistocene, the oceanfront was located 50 to 75 miles to the west. The ancient coastal dune, which runs from the Potomac River mouth in the north to Cape Lookout in North Carolina, 200 miles long, is the Suffolk Scarp. It’s a hill of yellow sand 28 feet above tidal water.

Consider: Why is the western shore of the Chesapeake Bay (25 feet high) in its present location? The Suffolk Scarp. If you drive Route 10 from Smithfield to Suffolk, why does the marsh on the left at Lone Star Lakes rise to farms on the hill to the right? The Suffolk Scarp.

If you enter the Great Dismal Swamp at the Jericho Ditch, why does the road drop 25 feet right at the entry gate? The Suffolk Scarp. And when Norfolk is 10 feet underwater, why will Smithfield and Suffolk be high and dry? You guessed it. The Suffolk Scarp.

There is a second Scarp, the Surry Scarp, 50 feet higher and to the west. The land between them is the Isle of Wight Plain, 20 miles wide at the James River, 50 miles wide at the North Carolina border. The land between them is very fertile. Lots of game. A good place to hunt and farm. Those Native American tribes chose wisely.

There’s another geological reason why Smithfield and Suffolk will be high and dry when Norfolk is 10 feet under: subsidence. Norfolk is sinking. 35 million years ago, the oceanfront was at Richmond. A bolide (comet, meteor, asteroid, whatever) crashed into the ocean just west of what is now Cape Charles. It created the sixth largest crater on planet Earth, 85 kilometers wide and 1.3 kilometers deep, as deep as the Grand Canyon.

The western rim of that crater, oddly enough, coincides with … the Suffolk Scarp. The land within the crater, Norfolk and the lower Eastern Shore (which was formed much later) is now subsiding slowly as its breccia compacts.

So Norfolk is sinking, while the land west of the Suffolk Scarp (from the Potomac River mouth, along Western Chesapeake Bay, through Smithfield and Suffolk, along the western Great Dismal Swamp, and South to Cape Lookout) is high, dry and stable. Twenty-eight feet high, dry and stable, west OF Tidewater.

Geology may not be exciting, but it sure can be interesting.

Susan and Bradford “Biff” Andrews are retired teachers who have been outdoor people all their lives, exploring and enjoying the woods, swamps, rivers and beaches throughout the region for many years. Email them at b.andrews22@live.com.