We all know that water can extinguish fire, and there’s no place with more water than the ocean. However, why is it that water there cannot extinguish a volcano?
When thinking about volcanoes, many might imagine a towering conical mountain emitting a thick column of smoke, resembling an erupting peak. Furthermore, after a volcanic eruption, a large amount of white volcanic ash will fall across a vast area. Thus, many subconsciously believe that volcanoes can indeed spew fire.
Volcano erupting.
But upon closer observation of volcanoes, this is not the case. Because lava (magma) that erupts from a volcano is actually a high-temperature liquid, and fundamentally, it is completely different from fire.
Close-up photos of lava clearly show that it is a liquid. When we studied physics in school, we learned about the transformation of three phases of matter: gas, liquid, and solid, which are related to melting points and boiling points.
Lava (magma) that erupts from a volcano is actually a high-temperature liquid.
Taking water as an example, the melting point of water is 0 degrees Celsius, and the boiling point is 100 degrees Celsius. When the temperature is below 0 degrees Celsius, we see solid water – ice; when the temperature is between 0 degrees Celsius and 100 degrees Celsius, we see water in liquid form; when the temperature exceeds 100 degrees Celsius, water will become gas – steam.
When the temperature is below 0 degrees Celsius, we see solid water – ice.
Basically, all substances behave similarly, having melting points and boiling points, and changing phase states according to temperature. Magma is molten rock and due to its complex rock composition, the melting and boiling points of different components inside are heterogeneous, meaning most magma is actually a mixture of solid, liquid, and gas. In contrast, the fire that appears during a volcanic eruption is a process where flammable materials release light and heat. In this fire, the main components are carbon dioxide, water vapor, oxygen, nitrogen, and other gases.
What erupts from the volcano is magma.
After understanding that what erupts from the volcano is magma, and magma is a high-temperature molten substance and not fire, you will appreciate that when a submarine volcano erupts, the magma entering the seawater is similar to a hose continuously spraying hot water into a cold water tank – the cold water cools the hot water, but does not make the hot water disappear in the same way that water extinguishes fire. Thus, seawater cannot extinguish submerged volcanoes.
Since volcanoes are products of thermal and material circulation on a planetary scale, these volcanoes remain continuously active. The entire Earth actually operates according to basic laws of physics and chemistry, which we all learned in high school.
For instance, the formation and activity of volcanoes can be explained by the second law of thermodynamics – it sounds very technical, but it is very relatable to our lives: Heat always spontaneously flows from a high-temperature source to a low-temperature source.
Heat always spontaneously flows from a high-temperature source to a low-temperature source.
If we trace back the evolutionary history of Earth over 4.6 billion years, we can see the effects of this law: About 4.6 billion years ago, Earth gradually formed through the collision of countless planets, and the energy from this collision was converted into heat, making the Earth at that time resemble a giant magma sphere (with the entire or most of its surface being magma), and its surface temperature reaching thousands of degrees Celsius.
Then, as magma can flow, heavier materials sink while lighter materials rise. As the heavier materials sink, gravitational potential energy converts into thermal energy; simultaneously, the originally scattered radioactive elements within the planets gather together, continuously decay, and simultaneously release energy.
These energies keep the magma inside the Earth continuously heated. However, since the ambient temperature of the universe is very low, averaging -270 degrees Celsius, Earth continuously radiates heat outward as thermal radiation (there are 3 methods of heat transfer: conduction, convection, and thermal radiation, but the universe is a vacuum, lacking a medium, so Earth can only radiate heat outward in the form of thermal radiation). Because heat is being transferred away, Earth must cool down, with its surface cooling first, causing the magma here to solidify into rock, forming the initial crust.
Earth gradually formed through the collision of countless planets.
To date, Earth has developed a structure that is basically made up of 3 layers: the crust, mantle, and core, with temperature increasing as one moves from the crust to the core. At the same time, because heavy materials continue to sink, its density increases – the average density of the crust is 2.8g/cm3, the average density of the mantle is 4.59g/cm3, and the average density of the core is 11 g/cm3. Thus, we can also think of the crust as “floating” on the mantle – similar to a board floating on the water’s surface.
Since the crust is very thin compared to the mantle and core, the average thickness of the crust is only about 17km (33km for continental crust and 10km for oceanic crust). In contrast, the thickness of the mantle reaches 2,850km. Therefore, the movement of the mantle will cause these thin solid layers to be torn apart and move along with the mantle.
Parts of the Earth’s crust that are torn apart become plates, and as the Earth’s crust moves, some will collide with each other while others separate.
Magma can flow, heavier materials sink while lighter materials rise.
Common sense suggests that the boundaries of these separating plates are very thin and fragile, and the underlying material can easily break through the rock layer and be pushed to the surface – here forming a long volcanic belt along the plate boundaries.
As the plates move further apart, magma cools after erupting at the plate boundaries, forming a thin layer, which is the oceanic crust – because it is much thinner than the interior of the plate, it will sag more than other areas, and over time, water will accumulate to form oceans.
Submarine volcanoes are essentially the result of plate movement.
In fact, oceans are formed in this way, and the formation of oceans is closely related to plate movement.
Therefore, submarine volcanoes are essentially the result of plate movement, and most of them are at the boundaries of separating plates. Since World War II, as humans have increasingly explored the oceans, we have discovered long submarine volcanic belts, mostly located in the middle of the oceans, known as mid-ocean ridges. They are the longest mountain ranges in the world, with a total length of about 80,000km.
