Science Lab: Deep-Sea Volcano

Did you know volcanoes can occur underwater? Did you know there are mountain chains underwater, too? The mid-ocean ridge is the longest mountain chain on Earth—it is 40,000 miles long! And it has hydrothermal vents that spew extremely hot water up into the cold ocean. These vents are located more than 12,000 feet below the surface of the ocean. The water from these vents is full of minerals and bacteria that, at a temperature of 750°F, combine to create an extreme environment in which certain organisms thrive.


What causes underwater volcanoes?


  • Adult

  • Small plastic bottle with a narrow opening

  • Kitchen tongs

  • Large plastic jar with a wide opening

  • Hot and cold water

  • Food coloring


  • Make sure the small bottle fits completely inside the large jar.

  • Pour cold water into the large jar so that it is three-quarters full.

  • Ask an adult to heat some water. The water should be hot but not boiling.

  • Have the adult pour the hot water into the small bottle and use the tongs to put the bottle into the jar. The bottle should sit below the water level in the jar.

  • Add some food coloring to the water. What do you see?


Hot water is less dense and lighter than cold water. So in this experiment, when the hot water in the bottle hit the cold water in the jar, the hot water rushed up to the surface, creating a small volcano.

Our planet is made up of a hot molten core, a thick mantle that surrounds the core, and a thin crust of rock plates that covers the mantle. The plates form our continents and oceans. Heat and pressure from the core boil up and cause the plates to move and shift, leading to earthquakes and volcanoes. Molten rock from the core meets frigid seawater, cooling to form mountain ranges such as the mid-ocean ridge.

Cracks in the mountains allow cold seawater to flood down to the core, where it is heated to extreme temperatures. Because hot water is less dense than cold water, as we saw in the previous experiment, the now-boiling seawater bubbles back up through these hydrothermal vents and we have an undersea eruption. Some of these vents are several stories tall!

Who could possibly live near these sweltering, acidic vents? Many of the species that live in this climate are brand new to scientists, who have only recently started exploring this area of the ocean. There are bacteria, shrimplike creatures, tubeworms, mussels, clams, and many others.


Do the experiment again and try mixing food coloring to see what happens.

Draw your deep-sea volcano here.


Go Diving!

The Great Barrier Reef in Australia is the largest coral reef on Earth and the biggest living construction made up of tiny organisms. The reef is about 1,600 miles long.

Why did the ocean wave?

It wanted to say hello.

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