The Isthmus of Panama seems to have occurred when land on the western Caribbean plate, now described as Central America, overrode the Cocos plate located in the Pacific Ocean. From the map of plate tectonics (image upper left) the proximity of the Caribbean, Coccos and Nazca plates can be observed along Costa Rica in Central America. During this subduction event the Cocos plate was pushed downward below the Caribbean plate and given exposure to internal heat, becomes molten rock. The building pressures from subductions result in lava and hot gasses that rise underneath the Caribbean plate producing volcanoes.
A map of ocean trenches in the Pacific show the presence of the Middle America Trench (image lower right).
All along the Middle America trench, undersea volcanoes erupted until peaks emerged above sea level. As land mass continued to increase and a connection between North and South America emerged, the Isthmus of Panama was formed. Prior to formation of this isthmus, warm water currents had run north along northeastern South America through the Caribbean and into the Pacific. With emerging Central America acting as a land bridge, warm northerly flowing ocean stream water was deflected through the Gulf of Mexico reinforcing the Gulf Stream that brings warm waters to North Americas East Coast.
Two conditions are thought necessary for an ice age, cool continental temperatures and air moisture for falling snow. Speculation suggests that by diverting the flow of warm Atlantic waters from the Pacific into the North Atlantic that the Pleistocene ice ages may have been triggered. The Pleistocene ice age generated massive glaciers that covered northern lands and provide much of the recent geological structure observed in Deerfield today.
