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How does a geyser work?

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Quick answer

A geyser erupts when water deep underground is heated past its boiling point by hot rock, but is kept liquid by pressure. When enough of it flashes into steam, the expanding steam shoves the water above it out of the vent in a violent jet.

A geyser works when underground water, heated by Earth's deep heat, builds up pressure until it erupts in a jet of steam and water. Water trapped in narrow channels boils, and the sudden pressure release sends it bursting to the surface.

Step by step

  1. Rain and snowmelt seep down through cracks toward hot volcanic rock.
  2. Pressure from the water above keeps the deep water liquid even above 100 °C.
  3. The trapped water keeps heating until some of it suddenly turns to steam.
  4. The steam expands violently and pushes the water column upward.
  5. The drop in pressure lets more deep water flash to steam, driving a full eruption.
  6. The chamber refills with cool groundwater, and the heating cycle begins again.

Key things to understand

  1. Groundwater seeps down near hot volcanic rock.
  2. The deep water heats well past normal boiling, held down by pressure.
  3. Eventually some flashes to steam, expanding violently.
  4. The expansion blasts water and steam up through the vent.
  5. After erupting, the system refills and the cycle repeats.

Labelled diagram

  1. Surface vent

    The opening where water and steam burst out.

  2. Narrow channel

    A constriction that traps water and holds back pressure.

  3. Water column

    Cooler water above presses down on the hot water below.

  4. Hot rock

    Magma-heated rock supplies the heat that drives the cycle.

  5. Steam chamber

    Water flashes to steam here, expanding and forcing an eruption.

How a geyser erupts from underground

Real-world examples

  • Old Faithful in Yellowstone erupts roughly every 60 to 90 minutes, though the interval varies.
  • Strokkur in Iceland erupts every few minutes, throwing water 15 to 20 metres high.
  • The geysers of El Tatio in Chile sit high in the Andes and erupt at dawn in cold air.
  • A pressure cooker works on the same principle: trapped steam builds pressure until released.

Common mistake

✗ Myth: People often think a geyser is simply a hot spring that boils over.

✓ Fact: A geyser needs a narrow, constricted plumbing system that traps pressure until it releases suddenly. A hot spring has a wide, open channel, so heat escapes gently and steadily instead of building to an eruption.

People also ask

What makes a geyser erupt?
A geyser erupts when superheated water deep underground suddenly flashes into steam. Pressure from the water above normally keeps that water liquid even above boiling point. When enough turns to steam, the expansion forces the whole column up and out of the vent. The eruption stops once pressure drops and the chamber refills.
Where are geysers found?
Geysers exist only in a few places where volcanic heat, abundant groundwater, and the right rock plumbing all meet. Most are in Yellowstone in the United States, Iceland, New Zealand, and Russia's Kamchatka Peninsula. A few smaller fields sit in Chile, Japan, and Papua New Guinea. They are rare because all three conditions must occur together.
How is a geyser different from a hot spring?
A hot spring releases heat steadily, while a geyser stores pressure and releases it in bursts. Hot springs have wide, open channels, so hot water rises and flows out continuously without building pressure. Geysers have narrow, twisted channels that trap water and let pressure build until steam forces an eruption. That constricted plumbing is the key difference.
Why are geysers rare?
They need a precise combination of abundant groundwater, intense underground heat, and a particular plumbing of narrow channels.
Why do some geysers erupt on a schedule?
Their underground chambers refill and reheat at a fairly steady rate, so pressure builds to the eruption point at regular intervals.

Part of the guide: Water & Weather Phenomena →