Book 12, Question 23
Why Does Cooling Lava Crack?
As lava cools, it shrinks. When rock shrinks, it pulls apart and cracks, a bit like mud drying in the Sun. In thick flows, those cracks can make six-sided columns!
More fun facts
- When thick basalt lava cools, it often cracks into six sided columns called columnar joints.
- The Giant's Causeway in Ireland and Devil's Postpile in California are famous examples.
- At a cooling lava lake in Hawaii, scientists heard and recorded the cracks forming one by one.
- A lava flow about 4.5 meters (15 feet) thick can take more than 130 days to cool to about 200 degrees Celsius.
- Columns give clues about how a lava flow cooled.
Sources: U.S. Geological Survey, U.S. Geological Survey
Questions kids ask
Why are the columns six sided?
Cooling basalt tends to crack in a hexagon pattern.