Sinkholes typically develop slowly as bedrock is whittled away by water turned acidic from absorbing carbon dioxide and interacting with plants. Rainwater obviously plays a role, but unseen water also matters. As the acidic water dissolves rock, it carves out conduits, or underground passages, for water. These conduits in turn help to develop underground basins known as recharge areas. Recharge areas contribute to the formation of sinkholes as water flowing to and from them and into the subsurface (the earth overhead) erodes bedrock. When water floods a developing sinkhole, some of the topsoil and other material can be caught in the conduits, further trapping water and limiting its ability to flow outward.
A lack of water can contribute to sinkholes, too. In some underground cavities, water may actually be holding up a thin overhang of earth. If that water level falls, the overhang has no support and collapses.
Sinkholes appear all over the United States. Florida, with its frequent rains and marshy terrain, is usually id entified with sinkholes, but they're also prominent in Alabama, Kentucky, Missouri, Pennsylvania,Tennessee and Texas [source: USGS]. They generally develop in karst regions, a type of terrain known for soft bedrock [source: Southwest Florida Water Management District]. The U.S. Geological Service describes karsts as having many water elements, such as springs, underground streams, caves and, of course, sinkholes [source: USGS].
No comments:
Post a Comment