Synclines are formed when tectonic plates move toward each other, compressing the crust and forcing it upward.

What causes synclines to form?

A syncline is the downward arc or curve of a fold. A fold, in geology, is a bend in a rock layer caused by forces within the crust of the earth. The forces that cause folds range from slight differences in pressure in the earth's crust, to large collisions of the crust's tectonic plates.

What type of force creates a syncline?

When the Earth's crust is pushed together via compression forces, it can experience geological processes called folding and faulting. Folding occurs when the Earth's crust bends away from a flat surface. A bend upward results in an anticline and a bend downward results in a syncline.