hydrothermal vents - Google Image Search

A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water is released. Hydrothermal vents are commonly found in places that are also volcanically active, where hot magma is relatively near the planet's surface, e.g. at mid-ocean ridges.

Here is a definition and more information:

Hydrothermal vent - Wikipedia, the free encyclopedia

...and here are some pictures of hydrothermal vents from Google, and this an extended description that you might find helpful... 

 A hydrothermal vent is a fissure or opening in the Earth's crust where hot water, minerals, and gases are released from the Earth's mantle into the ocean. 

These vents are typically found near areas of tectonic activity, such as mid-ocean ridges, where magma rises to the surface and heats the surrounding seawater. 

 Hydrothermal vents can reach temperatures of over 400°C (752°F) and release a variety of chemicals, including hydrogen sulphide, methane, and iron sulphide. 

These chemicals can support the growth of unique and specialized ecosystems that are not found anywhere else on Earth. 

 At hydrothermal vents, water is heated by the magma below the Earth's crust and then released into the ocean through the vent. 

The hot water is typically rich in minerals and nutrients, which can provide a food source for a variety of creatures, including bacteria, tube worms, crabs, and other species. 

 The ecosystems that thrive at hydrothermal vents are called chemosynthetic communities, as they rely on chemicals instead of sunlight to produce energy. 

These communities are important in understanding how life can exist in extreme environments and can provide insight into the origins of life on Earth.