What if volcanoes stopped erupting?

A volcano is a place where hot, melted rock comes up from deep inside Earth.

What if every volcano went quiet, forever? Would we miss them?

Volcanoes are places where melted rock and gases from deep inside Earth reach the surface. They can be very powerful.

But volcanoes also do important jobs for our planet. What if every volcano stopped erupting, for good? In this thought experiment you can follow three paths: what happens to new land, what happens to soil and farms, and what happens to Earth's air over a very long time.

USGS describes volcanoes as having played a key role in forming and modifying the planet: more than 80 percent of Earth's surface, above and below sea level, is volcanic in origin.

This thought experiment switches volcanism off and asks what might change for land building, soil formation and the long-term exchange of gases between Earth's interior and its atmosphere. It cannot say how Earth's interior could stop; it reasons only from what volcanoes do today.

Some islands were made by volcanoes. The Hawaiian Islands are volcanoes!

In 1963, a brand-new island called Surtsey grew out of the sea near Iceland.

Volcanoes make land. USGS explains that the Hawaiian Islands are chains of huge, gently sloping volcanoes called shield volcanoes, including Kilauea and Mauna Loa. Mauna Loa's top is more than 28,000 feet above the deep ocean floor.

New land can appear in a lifetime. UNESCO says the island of Surtsey, about 32 kilometers off the south coast of Iceland, was formed by eruptions from 1963 to 1967. Scientists have studied it since 1964, watching seeds, plants, birds and tiny animals arrive.

USGS: the Hawaiian Islands are linear chains of shield volcanoes, an intra-plate chain formed as the Pacific plate moves northwest over an inferred hot spot. Mauna Loa rises 13,677 feet above sea level and more than 28,000 feet above the ocean floor.

UNESCO's World Heritage listing for Surtsey records a new island built by eruptions in 1963–1967 and protected from its birth. By 2004 it held 60 species of vascular plants, 75 bryophytes, 71 lichens and 24 fungi, and 89 bird species had been recorded there.

Let's pretend every volcano goes to sleep forever.

No new islands might grow. Soil might slowly get less rich. Let's find out why.

Now imagine every volcano quiet forever. No new islands like Surtsey might ever rise from the sea, and existing volcanic islands might slowly be worn down by waves and weather with nothing to build them back up.

Farm soil might slowly change too, because fresh volcanic rock would no longer arrive to break down into new soil. And over millions of years, the air itself might change. These are ideas: we reason from what volcanoes do today.

With volcanism halted, new crust and island building at hot spots and plate boundaries might cease, leaving erosion unopposed. Fresh volcanic material, which USGS describes as weathering into some of the most fertile soils on Earth, would stop being supplied.

The largest effect might be the slowest: NASA describes volcanoes as the slow carbon cycle's route for returning carbon to the atmosphere. Without it, atmospheric carbon dioxide might decline over very long times as rock weathering continued. These are reasoned ideas, not predictions.

Volcano rock slowly crumbles into soil. Plants grow very well in it.

Volcanoes also let out gases from deep inside Earth. Long, long ago, those gases helped make our air and seas.

Volcanic rock and ash slowly break down and weather into soil. USGS says these become some of the most fertile soils on Earth, which have produced plenty of food and helped civilizations grow.

Volcanoes also let gases escape from deep inside Earth. The most common one, USGS says, is water vapor. USGS explains that over hundreds of millions of years, gases from volcanoes formed Earth's earliest oceans and air, the ingredients that life needed.

USGS: volcanic materials ultimately weather to form some of the most fertile soils on Earth, whose cultivation fostered civilizations; water vapor is by far the most abundant volcanic gas, with carbon dioxide and sulfur gases also emitted. Outgassing over hundreds of millions of years formed the earliest oceans and atmosphere.

In NASA's description of the slow carbon cycle, subducted rock melts and releases carbon dioxide, which volcanoes vent, then fresh silicate rock begins the cycle again. Volcanoes today emit 130 to 380 million metric tons of CO₂ a year.

Many farms grow food on rich volcanic soil.

The heat inside young volcanoes can even make electricity!

USGS says the heat inside young volcanic systems has been used to make geothermal energy, electricity from underground heat.

Volcanoes still add carbon dioxide to the air, but NASA says people now add far more: about 30 billion tons a year from burning fossil fuels, 100 to 300 times more than all volcanoes. So the carbon question today is mostly about people, not volcanoes.

Volcanic heat is harnessed for geothermal energy (USGS), and Surtsey remains a protected natural laboratory for how life colonizes new land (UNESCO).

On carbon, NASA gives present volcanic emissions as 130–380 million metric tons of CO₂ per year against about 30 billion tons from human fossil-fuel burning, 100–300 times more. Today that volcanic flux is small next to human emissions, but NASA describes volcanoes as the way the slow carbon cycle naturally returns carbon stored in rocks to the air.