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Roger Weller, geology instructor                     

Columnar Jointing
Sang Marzan
Physical Geology
Spring 2009


                                        Columnar Jointing Around the World

            What is columnar jointing? Larry Gedney, in his article in Alaska Science Forum explains that as volcanic rocks cool after erupting onto the earth’s surface, they shrink. This shrinkage produces stresses that strain the rocks, causing them to crack. If the eruptive rock that cooled evenly is in contact with a flat surface, the cracks will grow at right angles to the surface and develop in three directions, each at 120 degrees to the other two. This leads to hexagonal, six-sided columns. (1)  

            My interest in studying columnar jointing around the world  can be traced back to my home country of South Korea.  Although born and raised in South Korea, I never had the opportunity to visit Jeju Island, a small, exclusive island 90 miles south of mainland Korea, until 2007. I was absolutely fascinated by the dark rough hexagonal patterns of these rocks in the ocean. I had no idea what columnar jointing was! They were just beautiful. This motivated me to research different columnar jointing. Most are six-sided columns and a few are three-sided and many are seven-sided formations. These are breathtaking and it is hard to realize that these patterns are formed naturally.   This is a columnar jointing formation on Jeju Island, Korea. This columnar jointing is approximately 30-40m height and is 1Km in width.

People are enjoying fishing while sitting on columnar jointing.

Another example is Fingals Cave found in Scotland. This formation shows larger columns in height and form along the entrance to the cave. This cave is associated with an Irish Folklore story. Finn Mac Cool and an Irish Giant went to fight their Scottish enemy, Finn Gall. Mac Cool drove the columns in place, one at a time, until the Causeway reached Scotland (Fingals Cave). Mac Cool was so tired from the hard work that he returned home to rest. Finn Gall followed the Causeway to Ireland. He found Mac Cool sleeping, and Mac Cool’s wife, a very shrewd woman, told Finn Gall that this was her baby sleeping. Finn Gall thought that this giant baby’s father must be of incredible size and that he would surely lose any fight. Finn Gall fled back to Scotland. As he did, he destroyed the Causeway; only the two ends of the Causeway survive to this day. (2)

This is a postcard featuring the columnar jointing at Fingal’s cave.

Another example of columnar jointing is Giant’s Causeway in Northern Ireland. Giant’s Causeway is formed of lava flows, sills, dikes, ignimbrites, and shallow intrusions of all compositions. Most columns are straight with parallel sides and diameters from a few centimeters to 3 m. The Causeway consists of nearly 40,000 interlocking basalt columns, some as tall as 36 feet. The tops of the columns from “Stepping Stones” lead from the foot of the cliffs before disappearing under the sea. (3)


This postcard shows the columns at Grand Causeway.
Most columns tend to have 5 or 6 sides but some have as few as 3 and as many as 7.

            Another example is Devils Post Pile in California. The high volcanic activity within Devils Post Pile is due to its geographic location. The monument is near the edge of the Long Valley Caldera, a 9- by 18-mile oval-shaped depression located 12 miles south of Mono Lake along the east side of the Sierra Nevadas in east-central California. This area of eastern California has produced numerous volcanic eruptions over the past three million years, including the massive eruption that formed the caldera 760,000 years ago. The formation of Devils Post Pile began when basalt lava erupted 100,000 years ago in the valley of the Middle Fork of the San Joaquin River. As lava flowed from the vent, it filled the valley near the Post Pile to a depth of 400 feet, possibly pooling behind a natural obstruction. (4)


This picture shows how the flaring joints pass smoothly into perfectly regular columns.

Another example is Devil’s Tower in Wyoming. This Columnar Jointing is an igneous intrusion in northwestern Wyoming that cooled and formed prominent columnar jointing before being exposed by erosion. Devil’s Tower (Lakotaimato Tipila, which means “Bear Tower”) is a monolithic igneous intrusion or volcanic neck located in the Black Hills near Hulett and Sundance in Crook County, northeastern Wyoming above the Belle Fourche River. It rises dramatically 1,267 ft (386 m) above the surrounding terrain and the summit is 5,112 ft (1,558 m) above sea level. This Devil’s Tower has American Indian legends to tell. The story is about six Sioux girls who were picking flowers when they were chased by bears. Feeling sorry for them, the Great Spirit raised the ground beneath the girls. The bears tried to climb the rock, but fell off, leaving their scratch marks on the sides.(5)

From bottom to top can see flaring columns, extremely regular columns,
slightly undulose columns, and columns with horizontal jointing.


This is a map of how to get to Devil’s Tower

            Interestingly, I found a columnar jointing on Mars by searching the web. According to an Astrogeology team in Flagstaff, the unique fractures in lavas on ancient Mars suggest water occasionally flooded portions of the Planet’s surface. The fractures, known as "columnar joints," are the first that have been observed on a planet other than Earth. "Columnar joints form as cooling lava contracts," said Moses Milazzo, a geophysicist with the U. S. Geological Survey Astrogeology team in Flagstaff. (6)

A columnar jointing on Mars.

            Another example is Hong Kong High Island and Sai Wan. The Geopark's key rocks - columnar jointed tuff - formed as a mighty volcano collapsed, in an area that includes the south of the present-day Sai Kung Peninsula in the north and the Ninepin Group of islands in the south. Incandescent volcanic ash formed thick

layers in the caldera, and as it cooled to become rocks, cracks formed, creating hexagonal columns. Occurring around 140 million years ago, this was perhaps the last major event of Hong Kong's four phases of volcanic activity during the Jurassic and Cretaceous periods. (7)


There are excellent exposures of the tuff, with the columns very prominent, on the coast near the east dam of High Island Reservoir and around nearby Po Pin Chau.

Around the world, naturally formed patterns of six-sided columnar jointing are found to be amazing and beautiful. Columnar jointing across the globe, in high mountains and in the sea, may be short, tall, or curved. All keep the same pattern and basic characteristics of a hexagon, yet are unique in their development and location. Our GLG 101 class afforded me the opportunity to study these beautiful formations in detail.  I have really learned a lot in this class.

Works cited