The columns form due to stress as the lava cools. The lava contracts as it cools, forming cracks. Once the crack develops it continues to grow. The growth is perpendicular to the surface of the flow. Entablature is probably the result of cooling caused by fresh lava being covered by water. The flood basalts probably damned rivers. When the rivers returned the water seeped down the cracks in the cooling lava and caused rapid cooling from the surface downward. The division of colonnade and entablature is the result of slow cooling from the base upward and rapid cooling from the top downward.
One of the coolest things I have ever seen. Looks totally fake, like they built it for Fractal Falls in Polygon Gorge at Disneyland or something. Giants Causeway in Northern Ireland looks amazing as well. Check out several similar formations from around the world.