Erosional Features
- general lack of surface drainage or, if there is drainage it is commonly internal (within closed depressions) - View a map of Western Valley in Western Alachua County
- sinkholes also called dolines. There are four types of sinks recognized in Florida:
- Solution sinks (often shallow and w/gentle slopes) when limestone is near the surface
- Collapse sinks (deep and steep-sided) when the roof of caves collapse. Collapse sinks commonly form in association with changes in the water table such as severe droughts, significant rain events or increased water withdrawal. Deep, circular sinkholes with nearly vertical walls that extend below the water table are often called cenotes.
- Alluvial sinks, and
- Raveling sinks. More on Florida Sinkhole Types
- Caves
- When sinkholes grow together they form a karst valley, an elongated depression that may grow to several miles in size
- Where the water table is below the surface, rivers flowing in karst plains disappear in sinks and caves; such strams are called disappearing streams or stream to sink topography. If the river had a well developed valley, this valley will terminate abruptly at the point where the stream disappears and is called a blind valley.
- From the point where this surface water is swallowed, the water now flows in passageways as an underground stream. These underground streams which occasionally resurface in springs and river rises (O'Leno State Park is such an example, where the Santa Fe River disappears only to rise again downstream). Sometimes also, the roof over the underground river pathway collapses, resulting in a river once again at the surface but now channeled within steep walls. In places where the roof over the river is left standing, you get natural or rock bridges. In some cases the old river valley, carved when that stream flowed at the surface in the past, no longer carries any water because all the drainage is now underground and has become an abandoned valley. View a map of O'Leno showing most of these features
- If sinks become plugged with less permeable clayey or silty materials, water will accumulate in the depression creating perched lakes and ponds that last till the obstruction is washed away. This is true on a small scale as well as a large scale. For example, solution created a karst basin south of Gainesville called Payne's Prairie. It was drained by a sink (Alachua sink) which clogged in 1871, creating a 32 sq mi lake. Some 20 years later, the debris washed away into underlying solution cavities and since that time it has again been Payne's Prairie.
- When karst depressions or the surface of the land intersect the water table, the outflowing ground water may create springs, rivers, and lakes.
When sinkholes intersect, cockpit karst close spaced depressions and conical hills( the Arecibo radio telescope is located in one such sinkhole in cockpit karst in Puerto Rico.). Tower karst is a more extreme form of cockpit karst. As solution continues, the sinks get deeper and deeper until a layer resistant to solution is reached. From this point, solution can only proceed laterally. As the sinks coalesce, they create a limestone plain from which rise more resistant towers of limestone, up to 650' tall (Guilin, China).
Maps
Western Valley in Western Alachua
Approximately 180 mi2 (some12 mi wide x 15mile long) section of the Western Vally in Western Alachua County, including a small part of the Brooksville Ridge. Bat Cave lies in the lower third of the map near the Alachua/Gilchrist county line. Note the virtually total absence of stream drainage, excepting a small part of the Santa Fe River in the upper left hand corner of the map. (USGS 1:250,000 Gainesville, Fl. Quadrangle).
This is a segment of the USGS Arredondo, Fl 1:62500 15 minute Quadrangle. It was surveyed in 1890 and published in March 1894. As you can see, there have been some major changes in the Gainesville area in the last century! The red arrows highlight four examples of disappearing streams. The largest of these (#1) is a sink in Hogtown Prairie wherein disappears Hogtown Creek. Arrow #2 marks Alachua Sink a major sink at the northern edge of Payne's Prairie. The blue line that runs southeast from the sink is Prairie Creek which carries water from Newnan's Lake (off this map to the northeast) into the sink. Water from numerous creeks that drain the edge of Payne's Prairie (note Biven's Arm and Sweetwater branch in the center near the bottom) also empty into Alachua Sink. #3 is Lake Alice and an unnamed small creek near it. They both disappear into sinkholes. #4 represents several stream to sink features that drain a closed solution basin.
This is a composite of parts of two topographic quadrangles (Mikesville and High Springs, Fl) showing the course of the Santa Fe River. The river sinks in O'Leno State Park (arrow #1). From there it travels underground in caves and passageways to resurface at River Rise near the bottom of the map (arrow #2). Downing and Black Lakes (un-numbered arrows)are parts of the river's underground course where the roof of the passageways have collapsed, exposing the river briefly.
