Coal miners in Archbald, Pennsylvania (United States) set off a dynamite blast forty-five
feet below the ground to loosen a band of coal. After the explosion, they discovered a
huge, circular stone chamber full of about 300 carloads of smooth, round stones. They
had discovered the world’s largest natural pothole. It measured 42 feet wide and 50 feet
deep. The smooth stones inside had been a product of the whirling, harsh flurry of sand,
stones, and water that came from a melting Ice Age glacier and continuously ground into
the bedrock. Later, when the water and ice disappeared, the hole remained.
Potholes are often found in areas affected by similar ice age glaciation. They have many
shapes, some widening as they grow deeper, others slanting downward at an angle. Its
individual features depend on the kind of rock and the amount of water that created it.