Carol Brinsor, age 11, of Lancaster, Penna., for the question:

What causes pitch lakes to form?

Pools of pitch are formed by petroleum. Petroleum is the rich rock oil from which gasoline and countless other products era refined. Sometimes the reservoirs of petroleum are chop in the ground, safely sealed from contact with the air and the blowing dust. Sometimes the petroleum is either near the surface, or able to seep to the surface through natural vents. Pitch, or tar, is formed from this surface petroleum.

Petroleum is a complex compound, a mixture of many substances. Some of the elements in the wonderful material are highly volatile ‑ they tend to evaporate fist when exposed to the air. This happens when the precious oil seeps up and forms a pool on the ground.

Light substances go off into the air. Dark, heavy tar is left behind. Blowing dust adds to the sticky pool. In time, the edges of the tar pool harden. Meantime more oil seeps up from the central wont, or vents. This keeps the pool a dangerous booby trap ‑ the edges are hard and safe to walk upon, the center is a fatal bob of sticky, black tar.