Look for Evidence of Lava Flows

Lava flows leave behind many clues that help geologists understand how they flowed out of the volcano, as well as how quickly they cooled. Below are several clues left behind by the flow at the Columns of the Giants.

Columnar jointing happens as a result of stagnant pools of lava cooling slowly. As the lava cools and crystalizes into rock, the atoms in the lava become more organized and take up less space than when the lava was a hot liquid. As a result, the solidifying rock shrinks, causing cracks to form in the surface. The cracks radiate outward at 120-degree angles from one another, forming hexagonal shapes that lend the surface a honeycombed appearance. Over a cooling period of several decades, those cracks, called “joints,” also spread down through the solidifying rock, meeting other cracks spreading up from the bottom, and forming column-like shapes.

Columns form perpendicularly to the surface that the original pool of lava rested upon. These columns will lean or appear bent if the bottom of the lava pool lies on top of surfaces that are uneven, such as a hill or stream channel.

When lava cools particularly quickly, cracks form in a disorganized fashion, resulting in small columns that point in seemingly random directions. Disorganized jointing and columns are called entabulatures. The bulky-looking rock sitting atop the Columns of the Giants in the opening image is a great example of entablature.