Can volcanoes create water?
Volcanoes give off water. Lots of it — more water than anything else they give off. But “giving off” and “creating” are different things, and the gap between them is the whole of this page.
AI reconstruction — not a photograph · Shutterstock AI/Shutterstock.com · Shutterstock Standard License
Where a volcano’s water goes, in three steps
- 1. Water in the rock beforehand
- 2. Vapor vented from volcanoes
- 3. Condensed and rained down on the oceans
What comes out of a volcano
“Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide.”
U.S. Geological Survey Open-File Report 95-85, Volcanic Gas. Credit: U.S. Geological Survey.
That surprises most people. Ask anyone what comes out of a volcano and they will say lava, or ash, or choking fumes. The honest answer is steam, with everything else a distant second.
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Did that water help fill the oceans?
“Research has shown that some of Earth’s water originated through vapor vented from volcanoes; that vapor condensed and rained down on the oceans.”
NASA Science, “NASA-Led Team Links Comet Water to Earth’s Oceans”, 3 December 2024. Credit: NASA.
Read that carefully, because the careful reading is the point. Some of Earth’s water. Not all of it. NASA is describing one contribution among several, in an article whose main subject is a competing idea about comets — and the same article says outright that how Earth ended up with its water is still argued over.
So: does a volcano make water, or just let it out?
Here is where this page stops, and it stops on purpose. Water coming out of a volcano has to have been in the rock beforehand — steam does not appear from nothing. Whether that water was locked in the rock since the Earth formed, or soaked down from the surface and came back up, is a question this site holds no source for.
Both are real possibilities. Both are studied by people who measure things we cannot. What we can tell you is what USGS and NASA say in the sentences above, and that neither of them says a volcano makes water out of anything that was not water already.
“We do not know” is a real answer, and it is a much better one than a confident sentence with nothing behind it.
Where this fits
If a volcano is mostly moving water around rather than making it, that fits everything else on this site. Water changes state and changes place; the amount stays much the same. It is why a hot spring is rain that took a deep route home, why the water is billions of years old, and why the dinosaurs drank the water you drink.
For teachers
For school
Ages: a teaching choice, not a rule. The three steps in the diagram work from about seven; the careful reading of one small word, “some”, suits about nine upwards.
- The honest answer is steam, with everything else a distant second.
- NASA is describing one contribution among several, in an article whose main subject is a competing idea about comets — and the same article says outright that how Earth ended up with its water is still argued over.
- Water coming out of a volcano has to have been in the rock beforehand — steam does not appear from nothing.
Classroom prompt
Is “giving off” the same as “creating”? Ask the class to put the difference in their own words first, then read the USGS and NASA sentences again: which of the two does each one actually say?
Extension. Find a sentence somewhere else — a book, a quiz, a website — about where the oceans came from. Does it keep NASA’s word “some”, or does it quietly drop it?
Where this comes from
- The quotations
- U.S. Geological Survey Open-File Report 95-85 (public domain) and NASA Science, 3 December 2024 (used factually, without implying endorsement). Both read . Every quotation is verbatim.
- How sure is this?
- The composition of volcanic gas is measured directly and is about as solid as this site gets. Where Earth’s water originally came from is a reconstruction of events billions of years ago, and NASA’s own article calls it a debate — so this page reports both without settling it.
Where next
Where does volcanic water come from? sets out two routes, each described by a source: rain that soaks in and meets hot rock, and water carried down on a sinking plate. How are hot springs formed? is where the Park Service describes two ways that happens, and only one of them needs a volcano. Is there water inside Earth? shows where the table everyone quotes stops counting, and How much water is underground? is that table’s deepest row.