While the Gulf of Mexico is geologically passive, the region to the south is still very active. Five structures give an indication of geological history and active processes. Geologists suspect that the Gulf and Caribbean complex were created when continental fragments (Structure 1) collected between the Pacific and Atlantic. Later, similar fragments (Structure 2) sealed the region off from the Pacific. The volcanic arch (Structure 3) on the east and the deep trench in the middle (structure 4) are both indicators of continued seafloor activity. Most fascinating is a very small seafloor spreading center (Structure 5) at the bottom of the trench. Image courtesy of Gulf of Mexico 2002, NOAA/OER.