The three types of sinkholes and how they form: 
 

        1.  SOLUTION SINKHOLES

              Solution sinkholes form where soluble bedrock (i.e., limestone,
              dolomite, marble, and rock salt) is exposed at the land surface
              and thus subjected to weathering by dissolution.  Surface water
              collects in natural depressions and slowly dissolves a sinkhole. 
 

        2.  SUBSIDENCE SINKHOLES

              Subsidence sinkholes are similar to solution sinkholes, except
              that the soluble bedrock is covered by a thin layer of soil and/or
              sediment. Surface water infiltration dissolves cavities where the
              bedrock is most intensely fractured, and the overlying sediment
              gradually moves downward into the expanding cavity.
 

        3.  COLLAPSE SINKHOLES

              Collapse sinkholes form when surface materials suddenly sink
              into a subsurface cavity or cave.  The cavities form slowly over 
              time, as groundwater moves along fractures in soluble bedrock 
              and enlarges them through dissolution, and the actual collapse
              can occur in two different ways:  

              a.  When a cavity gets sufficiently large, the "roof" becomes too
                   thin to support the weight of any overlying rock or sediment,
                   so it collapses into the cavity.  

              b.  Caves are sometimes able to support the weight of overlying
                   sediments because they are filled groundwater.  However, if
                   groundwater levels are lowered, then the overlying sediment
                   will first erode and then collapse into the dewatered cavity.

                   Example:   Lake Jackson drains into the Porter Hole Sink!

                                    (The history of Lake Jackson reveals a pattern)

             Collapse sinkholes are a problem in states where caves occur.