Ward's World Activity Guides

39357_Ward's World+Columnar Basalt Activity

View, download, and print free resources for your science classroom.

Issue link: https://wardsworld.wardsci.com/i/1471526

Contents of this Issue


Page 1 of 2

Page 2 From a 2-dimensional bird's eye view, these columnar joints, or cracks on the tops and bottom of the rock, will look roughly like hexagons. As the basaltic magma continues to slowly and uniformly cool into basaltic rock, the cracks will penetrate up and down the rock and eventually meet. These cracks are called joints because the movement is within a rock instead of along a fault. The vertical columns will separate through natural erosional processes to display pristine columnar basalts. The more uniform and closely packed columnar basalts are, the less eroded they are. Why do Columnar Basalts form? It is not obvious why we observe these highly symmetri- cal geometric rock formations initially. Columnar basalts are repeatedly consistent in shape and size, suggesting that it is not a random act of nature. Like all processes under the laws of physics, nature will always choose to minimize energy. Since the magma has a long time to cool, the rocks naturally crack at the lowest possible energy geometry: intersections of ap- proximately 120 degrees. This suggests that when we see other basaltic rock formations not columnar in shape, the magma cooled more rapidly and irregularly jointed. Where are Columnar Basalts found? Columnar basalts are found where a mantle plume impinges upon the Earth's outer crust. During this type of volcanism, the volcanoes outpour thick, heavy, and high volumes of basaltic lava. These places are called flood basalt provinces. They are uncommon on Earth's surface today, but geologists have observed them sporadically throughout the rock record for much of Earth's history. Modern places to observe columnar basalts are Iceland, Ireland, and California, where active fault creates conduits for the deep mantle basaltic lava to access the outer crust. Columnar Basalt (continued) Columnar basalts at the Devil's Post Pile Natural Monument in California, USA. The bottom chunks are eroded column bits from the enact stack on top. + ward ' s science Cool Hot Heat flow Heat flow C C C C C Fig. 1: Diagram illustrating the relationship between inward cooling and columnar joints. Bird's eye view of columnar joints, demonstrating the first fractures to form in the jointing process.

Articles in this issue

Archives of this issue

view archives of Ward's World Activity Guides - 39357_Ward's World+Columnar Basalt Activity