Schematic cross sections of (a) a simple crater and (b) a complex crater showing idealized form, structure, and distribution of impact units. Simple crater forms are typical of structures with rim diameters of less than about4 kilometers (on Earth); above this transition, diameter craters are characterized by complex morphologies exhibiting central uplifts, shallow floor depths, and slumped rims. For complex craters with diameters of about 4 to 25 kilometers, the central uplift commonly (but not always) occurs as a single peak. Larger impact structures can have complex, ring-shaped central uplifts.

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