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ELI5 Yahaaa

Far, hard and facing you

Why Do Canyons Echo So Well?

Canyon walls are distant, hard and steep — the three things an echo needs.

Walls far enough for aclear delayHard rock that reflectsinstead of absorbingSteep faces aimingsound back at you
Three conditions, all met at once.

  1. Step 1 of 5

    Distance gives you the delay.

    Canyon wall 340 m away2 second delayRoom wall 5 m awayfar too short

    You need over a tenth of a second to hear the echo separately, which means a wall at least 17 metres away. Canyon walls are far further.

  2. Step 2 of 5

    Bare rock is an excellent reflector.

    Bare rock Reflects nearlyeverythingForest Absorbs — almost noecho

    Hard dense surfaces bounce almost all the sound back. Trees, soil and snow absorb it, which is why forests are so quiet.

  3. Step 3 of 5

    Steep walls aim it back at you.

    Vertical wall Sound returns to youSloping wall Sound is deflectedupward and away

    Sound reflects like light: the angle out matches the angle in. A near-vertical wall sends your shout straight back down the canyon.

  4. Step 4 of 5

    Two walls give you repeats.

    Your shout Bounces offone wall And off the other Fainter eachtimeRepeats

    Sound can bounce from one side to the other several times, each trip returning a fainter copy. That is the fading repeat you hear.

  5. Step 5 of 5

    Each bounce loses energy.

    First echoloudSecondquieterThirdfaint

    Some sound is absorbed at every reflection and some spreads away. The echo fades to nothing after a handful of trips.

    Some ancient amphitheatres were shaped deliberately so a whisper on stage reaches the back row clearly.

The short version

Canyons echo because their walls are distant, hard and steep — and two walls give repeating bounces.

Try it yourself

Shout across a valley with rock on one side and trees on the other. Only the rock answers.

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