The southeastern area of Orange Lake has a water depth of 1 to 3 m (3 to 9.8 ft). The primary karst features within this area are cover subsidence sinkholes and associated fissures (A-A’, B-B’). These features have type 2 and 3 characteristics (Track Map), where the overburden has subsided to accommodate loss due to solution in the underlying limestone. Less common karst features have also been identified, such as buried sinkholes, faults and dissolution pipes.

The large subsidence along the southern shore measured approximately 400 m (1312 ft) in diameter (A-A’). The surface expression is apparent on the lake bottom as a slight subsidence. Horizon HL (A-A’, type 2, HL) forms a depression filled by onlapping cover sediments. Several high-angle faults are present, with little vertical displacement. These features may also represent dissolution pipes. Leakage of lake waters to the aquifer in these and similar areas is controlled by the permeability of the cover sediments or proximity of the faults to the lake floor. Of the features identified in the southeast area, very few appear to breach the lake bottom.

A small number of depressions found in the southeastern area may be linked to more active sinkhole development (B-B’, type 3). The type 3 feature is smaller than the type 2 (~ 50m, 164 ft). The pattern of disturbed horizons implies active subsidence with intervening periods of deposition. As the sinkhole subsides, it is subsequently filled by sediment, seen as onlapping reflections within the depressions, followed by differential subsidence. Buried by <1 m (3.3 ft) of sediment, this sinkhole is an example of the composite mature subsidence sinkhole. A proposed model for subsidence sinkhole development is outlined in the figure below (B-B’ Diagram).