Thick lava shrinks as it cools and cracks

Why are hexagons favored?

They release stress efficiently

Columnar Basalt Quiz: Why Cooling Lava Cracks Into Hexagons

This columnar basalt quiz studies the giant stone pencils found on coasts and cliffs worldwide. Play 10 interactive questions on lava cooling and shrinking, cracks forming at right angles to cooling surfaces, why hexagons are common, the Giant's Causeway, Fingal's Cave on Staffa, Devils Postpile in California, Iceland's Svartifoss and Reynisfjara, and colonnade and entablature layers.

Start Columnar Basalt Quiz

🎯 Daily Trivia Challenge • 🧠 10 Questions • ⏱️ 150 Seconds

Question 1 / 10 Time: 150s

Rock
What rock commonly forms columnar joints?
Cause
Why do columns form?
Angle
How do the cracks grow relative to cooling surfaces?
Shape
Which column shape is most common?
Why
Why are hexagons favored?
Causeway
Which Northern Ireland site has about 40,000 columns?
Cave
Which Scottish sea cave is made of basalt columns?
US
Which California monument has basalt columns?
Iceland
Which Icelandic waterfall falls over dark columns?
Layers
What is the regular lower tier of columns called?

Explanations: answer key for all 10 questions

Q1: What rock commonly forms columnar joints?
Answer: Basalt
It comes from lava.
Q2: Why do columns form?
Answer: Thick lava shrinks as it cools and cracks
Stress opens cracks.
Q3: How do the cracks grow relative to cooling surfaces?
Answer: At right angles
They grow inward from top and bottom.
Q4: Which column shape is most common?
Answer: Hexagonal
Five and seven sides also occur.
Q5: Why are hexagons favored?
Answer: They release stress efficiently
Cracks meet at about 120 degrees.
Q6: Which Northern Ireland site has about 40,000 columns?
Answer: Giant's Causeway
Legend credits a giant.
Q7: Which Scottish sea cave is made of basalt columns?
Answer: Fingal's Cave
It inspired Mendelssohn.
Q8: Which California monument has basalt columns?
Answer: Devils Postpile
It is near Mammoth Lakes.
Q9: Which Icelandic waterfall falls over dark columns?
Answer: Svartifoss
Its name means black falls.
Q10: What is the regular lower tier of columns called?
Answer: Colonnade
The messy upper tier is the entablature.

Why Lava Cracks Into Hexagons

When a thick lava flow, usually basalt, cools, it shrinks. Stress builds and cracks open, growing at right angles to the cooling surfaces, inward from the top and bottom. The cracks join to form columns, and hexagons are most common because cracks meeting at about 120 degrees release stress efficiently, though five and seven-sided columns occur too.

Flows often show a regular lower tier of columns, the colonnade, and a messier upper tier, the entablature. Slower cooling generally makes thicker columns.

Famous examples include the Giant's Causeway in Northern Ireland, with about 40,000 columns, Fingal's Cave on Scotland's Isle of Staffa, which inspired Mendelssohn, Devils Postpile in California, and Iceland's Svartifoss waterfall and Reynisfjara beach. Legends often credited giants with building them.

What This Quiz Teaches

Geology fans will enjoy these questions.

How columns form
Why hexagons are common
Which layers exist
Where to see them
Which legends surround them

Did You Know?

Columns can be curved or fanned.
Some columns are tens of meters tall.
Mud cracks follow similar rules.
Lab experiments with starch mimic columns.
Columns can form in other lava types too.