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39357_Ward's World+Columnar Basalt Activity

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Page 3 Questions and Observations for Students: 1. Based on what you know about how the slow cooling rate encourages columnar basalts, what do you expect basalt to look like if the volcanic melt cooled quickly? If a basaltic volcanic melt cools quickly, the resultant rock will be amorphous and irregularly shaped, rather than repeated uniform prisms. 2. What is a household item that contracts as it cools down from liquid to solid? Liquid water to solid ice cubes. 3. Draw a 2-dimensional bird's eye representation of columnar jointing. How do these two-dimensional cracks form into 3-dimensional columns? (Students should draw a rough representation of various hexagons with shared edges, demonstrating columnar jointing results). When the surface and bottom of the basaltic magma initially begin to cool, we see surficial fractures like this. With inward, uniform cooling, the cracks penetrate up and down the rock, eventually connecting to form columns. 4. Look at your drawing. Can you think of a sedimentary environment that creates a similar pattern? What is it, and why does this happen? Mud cracks. Mud cracks harden in this pattern when they have sufficient time to dry and harden, analogs to a slow cooling rate. Like columnar jointing, mud will contract when it hardens and forms tensional cracks in the lowest energy geometry possible. Ward's Geologist Amelia sitting on top of an eroded columnar basalt. Columnar basalts eroded in half. Columnar Basalt (continued) + ward ' s science 5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com Find materials for this activity at wardsci.com. Discover more free activities at wardsworld.com

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