What are hydrothermal vents in the deep sea?

How it works

Vents are usually found near undersea volcanoes and where Earth's plates are pulling apart. Cold seawater trickles down through cracks in the rock, gets heated by hot magma (melted rock) below, dissolves minerals and then shoots back out of the sea floor.

When the hot water meets icy seawater, the minerals come out of it as dark clouds that look like smoke, so some vents are called black smokers. The minerals pile up into tall chimneys. The deep sea is under enormous pressure, so the water can be well over 100 °C without boiling.

No sunlight reaches the vents, so plants cannot grow. Instead, bacteria use chemicals such as hydrogen sulfide to make food, a process called chemosynthesis. Giant tube worms keep these bacteria inside their bodies and live on the food they make, while crabs, shrimp and clams gather nearby.

Where to see it in New Zealand

North of New Zealand, the Kermadec region has a chain of undersea volcanoes where scientists have found hydrothermal vents. On land, Pōhutu Geyser at Whakarewarewa in Rotorua works on a similar idea: groundwater heated by hot rock underground bursts out at the surface.

Try it together

With an adult's help, fill a clear tub with cold water. Fill a small bottle with warm tap water and a drop of food colouring, tie a string around its neck and gently lower it, uncapped, to the bottom. Watch the coloured warm water rise like a vent plume.