The geologic feature that forms when a central crack where a thin section of crust breaks and molten rock seeps out is a fissure volcano.

Here's why:

* Fissure: The crack in the crust is called a fissure.

* Thin section of crust: This indicates that the crust is relatively weak and easily broken.

* Molten rock seeps out: This refers to the eruption of lava, which is molten rock.

Fissure volcanoes are characterized by long, linear vents from which lava flows out. They are often found in areas where tectonic plates are pulling apart, creating thin and weak crust.

Let me know if you have any other questions about geology!