Lulworth Cove was formed when the sea broke through the outer layer of hard Portland Stone to scoop out the softer Wealden deposits. Stair Hole is another cove in the making and eventually the two will merge and form an even larger cove.

Stair Hole is a popular destination for Geology Field Trips. Southampton University has performed a geological survey which is documented in:- Stair Hole.

Stair Hole	Sea breaking through Portland Stone
Softer Wealden deposits removed	Will eventually merge with Lulworth Cove