The Mariana backarc, the same location of the deepest point on Earth, is where the thermal vents occur due to the spreading of two plates. In other words, the spreading apart of the sea floor results in a trench like the Mariana trench. At such backarcs, and the similar but not the same Mid-Ocean Ridges, “black smokers” form.
The following video is a fly-thru movie at the Mariana backarc in search for HydroThermal vents (second video).
Hydrothermal vents at a depth of 3500 m at the Mariana trench. The temperatures of the (black) fluid exiting the vents reaches 300-400 degrees centigrade triggering the proliferation of a dense life form ecosystem. Such vents/chimneys can reach 60 meters high. In the video they measure it to be 30 meters high. How amazing is this?
These are videos from the 2015 Hydrothermal Hunt by the Earth-Oceans Interaction Program, NOAA, and support by the Schmidt Ocean Institute.
This video summaries the the cruise and is full with surprises of amazing explorations. Two of the surprises is the discovery of lava flow (as compared to previous scanning of the area) and the detection of the Helium 3 isotope which is assumed to be entrapped within the solid Earth and only released through volcanic eruptions or hydrothermal vents.