Other common features are high-frequency or chaotic reflections interspersed between horizontal reflections (Type 4). These reflectors indicate a disturbance within a relatively intact stratigraphic sequence and may represent solution pipes or fractures through the overburden. The features may connect to dissolution systems in the underlying limestone and could represent direct hydraulic connection through the semi-confining layer to the underlying aquifer. The disturbed reflections indicate areas of potential subsidence or collapse. These features have a high potential for reactivation since the plugs that fill solution pipes may dislodge during periods of major rainfall variations. There are many examples of this from Marion County (Cain and Hornstine, 1991). Solution pipes and related features commonly occur in areas where cohesive overburden is moderate to thin. Dissolution is focused and material directly over the cavity is washed into the void during the piping process. Type 4 features are widespread throughout the lakes surveyed, they occur in all phases of karst development and are commonly associated with poljes.

The Type 5 feature represents the classic collapse sinkhole, with steep walls that show evidence of slumping and active development along the periphery of the collapse. Freshwater plumes have been imaged emerging from similar collapse features found in marine environments (e. g. Crescent Beach Spring). In seismic profiles, areas of negligible acoustic return below the collapse have been postulated to represent subterranean cavities. These active phase collapse sinkholes are typically evident at the surface without imaging and occur in areas of minimal overburden. They also indicate areas of internal drainage or discharge depending on the location of the potentiometric surface of the Floridan aquifer.