A lighthouse does not stay loyal to the sea; the sea abandons it. At the cliff edge, hydraulic pressure, abrasion by suspended sediment, and chemical weathering work together as a quiet demolition crew, enlarging joints and bedding planes in the rock until blocks detach and crash away from the base.
What looks like a fixed frontier is really a moving boundary, because wave energy focuses on the cliff foot, undercutting it to form a notch that destabilizes the rock mass above and promotes rotational slumps and planar failures described in rock mechanics. Each collapse removes the old edge, letting the shoreline line shift landward by centimeters or less per storm, yet those tiny increments accumulate across long spans into wholesale coastal regression.
The apparent inland march is therefore not a walk but a subtraction. Structural geology sets the fracture pattern, sea level sets the attack height, and littoral transport sweeps debris away so the process can repeat; the lighthouse stays put on its foundation while the continent itself is pared back around it.
