How Volcanoes and Hot Springs on the Seafloor are Linked

The rocks near the mid-ocean ridge are full of cracks because of the rapid cooling of the lava and from faulting. Seawater seeps down into these cracks and as it works its way downward it can be heated up by the rising magma from below. When the water deep in the cracks is heated up, it becomes less dense and begins to rise, again like a hot air balloon. Although the water is very hot, hundreds of degrees C, it does not boil (remember that water normally boils at about 100°C). It does not boil because of the pressure from the weight of a couple miles of water on top of it. The hot water, usually about 350°C spurts out on to the seafloor in submarine geysers.

The hot water dissolves some of the minerals in the basalt rock it passes through and so it is no longer very much like normal seawater. It is rich in metals and sulfur. When this hot fluid comes in contact with the cold seawater on the seafloor, minerals suddenly form. The minerals turn the water black and it looks like black smoke billowing out of cracks in the seafloor- that is why they are called “black smokers”. If the water continues to come out of the same spot or vent for a long period of time mineral deposits can build up and create weird-looking spires and mounds that can be tens of meters high—like large chimneys.

The hot water that comes out of the seafloor provides food for tiny one-celled creatures called microbes. Many of the microbes live off the sulfur that is in the hot water. The microbes cannot live in the super hot water that comes out of the vents, but instead live in cooler areas where the hot water has mixed with cold seawater. The oceans are so large that they hardly heat up at all even though there are many hydrothermal vents blasting hot water on to the seafloor. Larger clams, mussels, and long tube worms also live off the warm mineral-rich water. Shrimp eat the microbes and in turn are eaten by larger animals that live around the vents.

Most of the seafloor is like a desert with almost no signs of life, so the areas around the hydrothermal vents are like an oasis with lots of animals all densely clustered together. Another interesting thing about these animals is that they live on the bottom of the ocean where there is no light, so there is no photosynthesis for the kind of plant life that we see all around us. The vent animals are called a chemosynthetic community because they rely mainly on chemical nutrients. It is interesting to see how the microbes and larger animals that live off of them are all basically eating the rocks on the seafloor. The hot water delivers the parts they can eat from deep beneath the rift.