The correct option is 2 and 3 only.
Explanation
Groundwater acts as a significant erosional agent in regions composed of soluble rocks such as limestone, dolomite, or gypsum. The chemical process of solution and precipitation creates a distinct landscape known as Karst topography.
Statement-wise Analysis:
- Statement 1 is Incorrect: Sinkholes are typically circular or funnel-shaped depressions, not square-shaped. They range in size from a few square meters to hectares and vary in depth. They are the most common landforms in Karst regions.
- Statement 2 is Correct: While some sinkholes form solely through surface solution, others form when the roof of an underground cave or void becomes too thin to support the weight above. When the bottom of a sinkhole or the roof of a void collapses, the resulting depression is termed a collapse sink (or doline).
- Statement 3 is Correct: Lapies refer to an irregular geomorphic feature characterized by grooved, fluted, and ridged rock surfaces. These form due to differential solution activity along the joints and cracks of limestone pavements, leaving behind sharp ridges and deep trenches.
Key Takeaway:
Sinkholes are circular depressions formed by solution; collapse sinks involve the structural failure of underlying voids; and lapies are surface features resulting from the etching of limestone along joints.