Why aren't underwater volcanoes extinguished by the sea?

It's a scene we often see in disaster movies and television: volcanoes erupt beneath the sea, churning out terrifying eddies and waves...

Faced with this picture, a question has crossed many people's minds:

Why aren't underwater volcanoes extinguished by the sea?

A volcano is not a fire-breathing mountain

Before we can understand this problem, we need to correct some people's wrong impression.

When many people think of a volcano, the first thing they think of is a tall, cone-shaped mountain, belching out huge columns of smoke -- it looks like a mountain breathing fire.

After a volcano erupts, a large amount of white ash falls over a large area. It is also very similar to the soot we see. It is fine particles of dust, which is off-white.

So many people subconsciously think that a volcano is a mountain that breathes fire. But if we zoom in and look at the volcano up close, it's not like that at all.

Because the lava that erupts from volcanoes is actually a hot fluid, not different in nature from water, but quite different from fire.

In many close-up photos of lava, it's clear that it's often indistinguishable from a liquid.

When we learn physics as children, we know that matter exists in three phases: gas, liquid and solid. Related to the change of phase state are the melting and boiling points.

Take water for example, the melting point of water is 0℃, the boiling point is 100℃, when the temperature is below 0℃, we see solid water - ice;

When the temperature is between 0℃ and 100℃, we see liquid water;

At temperatures above 100 degrees Celsius, we see water in the gaseous state of vapor.

Basically all matter does, it has a melting point and a boiling point, and it changes phases depending on temperature.

Magma, on the other hand, is molten rock -- most magma is actually a mixture of solid, liquid and gas because of the complex composition of the rock and the different melting and boiling points of the different components within it.

Flame, by contrast, is the process by which combustible materials release light and heat and various chemical products during combustion.

In a flame, the main material components are carbon dioxide, water vapor, oxygen, nitrogen and other gases. Now that we understand that what volcanoes spew out is magma, and that magma is hot melt, not fire, we should be able to understand that when an undersea volcano erupts, magma enters the water like hot water in a cold tank, rather than a fire erupting from the ocean floor.

Cold water cools the hot water, but it can't extinguish it like a fire unless we manually turn off the hot water faucet.

Where do underwater volcanoes come from?

So the problem here is, since an underwater volcano is like a faucet spewing out hot water, the water cools the magma and turns it into rock.

Surely the sheer volume of ocean water would solidify the magma that's spewing out, clogging the crater and making it impossible for undersea volcanoes to erupt?

The answer is no.

Because volcanoes are actually the product of planet-level cycles of heat and matter, they won't stop until the Earth dies.

The whole Earth actually operates according to basic physical and chemical laws, which are not profound.

The formation and activity of volcanoes, for example, can be explained by the second law of thermodynamics -- which sounds technical, but one of its statements (Clausius's) is very close to home: heat flows spontaneously from a hot reservoir to a cold one, not the other way around.

If you look back over the 4.6 billion years of Earth's evolution, you'll see this rule in action:

About 4.6 billion years ago, Earth was gradually born out of numerous collisions of planetesimals, whose energy was converted into heat.

As a result, the Earth was a giant magma ball (all or most of its surface is magma) with surface temperatures of thousands of degrees Celsius.

The ring in this image was created by the impact of countless asteroids that left Earth as a red ball of magma.

Then, because magma is mobile, heavy stuff sinks and light stuff comes up (see, here's another rule of physics).

When heavy material sinks, gravitational potential energy is converted to heat energy; Meanwhile, the radioactive elements that would otherwise have been scattered in planetesimals would have pooled together, decaying and releasing energy.

This energy keeps the magma inside the Earth heated.

But at the same time, because the background temperature of the universe is very low, with an average temperature of -270℃, the Earth continues to transfer heat outward in the form of thermal radiation (heat transfer in three ways:

Heat conduction, heat convection, heat radiation, but the universe is a vacuum, there is no medium, so the earth can only transfer heat in the form of heat radiation.)

Since that heat was transferred, the Earth must have cooled -- the surface cooled first, so magma here would have cooled first to form rock, the first crust.

Up to now, the earth has evolved into a three-layer structure of crust, mantle and core, and its temperature is getting higher and higher from the crust to the core.

At the same time, as heavy material sinks, it gets denser and denser -- the crust averages 2.8g/cm3, the mantle 4.59 g/cm3, and the core 11 g/cm3.

So we can also think of the crust as "floating" above the mantle -- just as a board floats on water. At this point, we can think of the earth as a hot pot

The core is a furnace, powered by gravitational potential energy and radiative heat;

The mantle is the base of the hot pot soup, because the furnace is heating up;

The crust is a cabbages floating on top.

Under the heating of the core, the mantle creates constant convection of heat -- hot mantle moving up from the core and cold mantle material drilling down from beneath the crust.

Some people think that the mantle cycle is the whole mantle cycle, while others think that the upper and lower mantle cycle separately. Photo credit: wikipedia

The crust, on the other hand, is very thin relative to the mantle and core, with an average thickness of only 17 kilometers (33 kilometers for continental crust and 10 kilometers for oceanic crust), and only about 100 kilometers for the lithosphere, which consists of the solid rock at the top of the upper mantle.

The mantle, by contrast, is 2,850 kilometers thick, so this thin layer of solid rock must have been torn apart by the mantle's motion

It's as if the cabbages on a hot pot are in motion because of the churning of the soup base.

The parts of the earth's crust that are being torn apart become plates, and as the earth's crust moves, the plates move, too, some colliding with each other and some moving apart from each other.

It's common sense that these separate plate boundaries are thin and fragile, and that the mantle material beneath them can easily break through the layers and spill out to the surface

This would create a long volcanic trail along the plate boundary.

And as the plates move further apart, the magma at the plate boundary cools, creating a thin layer known as the oceanic crust.

Because the ground here is much thinner than within the plate, it is naturally low-lying, so water will form the ocean.

In fact, that's how the oceans formed, and how they formed is related to plate motion.

We find oceans in all stages of growth right here on Earth:

Rift Valley - small ocean basin - mature ocean basin - dying ocean basin - dying ocean basin - fully closed ocean basin. This is known in geology as the Wilson cycle.

So underwater volcanoes are actually the result of plate motion, and most of them are located at the boundary where plates separate.

As we've explored the oceans since World War II, we've discovered long underwater volcanic bands, mostly in the middle of the ocean, called mid-ocean ridges.

They are the longest mountain range in the world, with a total length of about 80,000 kilometers.

Of course, there are other underwater volcanoes. Their formation is related to the activity of the mantle plume.

It's not uniformly heated everywhere in the mantle, and some of the mantle material is much hotter than the rest, and when it gets hot, it runs up, and it forms a mantle plume that goes right under the crust.

The mantle plume might have branched off from the top of the plume, and their activity would have broken through the thin oceanic crust and become a constantly spewing submarine volcano. The Hawaiian island chain had something to do with it.

In this theory, the position of the mantle plume is constant, but due to the movement of the Earth's crust (dark blue arrow), the plume forms a series of volcanoes on the earth's crust. The numbers are the years of the island's formation, in millions of years. For example, 4.89 million years would be 4.89 million years.

But whether it's a plate edge or a mantle plume, volcanoes form as a result of the circulation of heat inside the Earth, which can't be stopped by a thin layer of water on the surface alone.

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