Obsidian Flow Field

Obsidian Flow Field is an original illustration set in Central Mexican Volcanic Belt. It lies in the tropics, where the climate is subtropical highland — dry winters, mild summers.

Angular black blocks with smooth curved shell-like fracture faces lie across a cool high plain, thin amber edges catching the light where the glass is thinnest. A rough lobed lava-flow boundary crosses the ground. Sparse bunchgrass and low scrub grow around the edges of the flow.

Why does obsidian break into curved, glassy faces?

Obsidian is lava that cooled too fast to crystallise — volcanic glass, which is why it breaks in those curved conchoidal faces and holds a thinner edge than steel. It forms from silica-rich magma, the explosive kind. The lobed flow margin is still sharp and barely colonised by plants, so the eruption is geologically recent, and the cool air says considerable altitude.

Terpano is a free daily geography puzzle. You study one original illustration, place a pin on a borderless terrain map, and see how close you were. There is no account and no sign-up; progress stays in your own browser. It plays in 11 languages.