6
IN previous chapters there have been observations concerning the results of dissolving dolomite (magnesium limestone) with percolating, slightly acid water to produce caves, natural tunnels, and natural bridges. Such water is in part a mole-like introvert, but its activities may be dramatic when the roof of a cavern collapses to produce a sinkhole. Sinkholes may also be formed less dramatically by dissolving action slowly enlarging vertical fractures in dolomite or limestone.
The Rolla area contains three of the spectacular Ozark sinks: namely Conical, Slaughter, and King sinks. Conical and Slaughter sinks are on opposite sides of the road on Forest Service land 4 miles southwest of Jerome en route to Boiling Spring. Conical is about 100 feet deep by 300 feet in diameter and Slaughter is 175 feet deep by about a quarter of a mile in maximum diameter. Slaughter has nearly vertical walls and contains one of the many Ozarks Chimney Rocks and a small natural bridge. "Chimley" Rock is not an uncommon pronunciation in the Ozark dialect-a preservation of older English usage, for Sir Walter Scott refers to "…a kirk with a chimley in it" in Rob Roy. King Sink, northwest of Flat, is nearly half a mile long and 200 feet deep. Its walls are less vertical than those of Slaughter; thus Slaughter is the most impressive of the three.
The most spectacular sink in the Missouri Ozarks is Grand Gulf, 6 miles west of Thayer. It is a collapsed cave system half a mile long by 150 deep with a huge natural tunnel representing a remnant of the cave roof. Some 25 square miles of surface drainage go into Grand Gulf, through the tunnel, and back underground into the remaining portion of the cave system to emerge at Mammoth Spring, Arkansas, eight miles to the southeast, as demonstrated by fluoroscein tracer dyes.
The Sunkland, 3 miles southeast of Akers Ferry, is also a collapsed cavern nearly a mile long and 200 feet deep. It is not as easily accessible as Grand Gulf, but does hold the Missouri Ozarks record for length.
Sinkholes can be an engineering problem, and according to the "Beveridge Law of Sinks," if an attempt be made to construct reservoirs in sinkhole areas, water will leak out through them; but if surface drainage (for example storm sewers) be diverted into them, they will invariably become plugged and refuse to carry away the water.
A sinkhole system which didn't plug is that in the valley of the Gasconade southeast of Richland where much of the flow goes underground to surface in the stream bed west of Waynesville. Gravel conceals the sinks, but U.S.G.S. Water Resources surface flow data leave no doubt regarding the Stygian stint.
As a concession to city dwellers who are denied the natural endowments of the Ozarks, reference should be made to Sinks Road in northern St. Louis County. This road is so named because it winds its way through an area crate red by sinkholes reminiscent of a saturation bombing pattern.