The dark distinctive depression on the summit of the icy mountain at the centre of this image of Pluto's surface is believed to be the giant, 56 kilometre-wide caldera of a recently active cryovolcano.

Geologists discovered the feature on the informally named Wright Mons while sifting through new images downloaded from NASA's New Horizons spacecraft.

They combined images of Pluto's surface to produce 3D maps showing two mountains, Wright Mons and Piccard Mons, which appear to be ice volcanoes, each more than 160 kilometres wide and four kilometres high.

Unlike volcanoes on Earth that spew out hot molten lavas, Pluto's ice volcanoes are thought to be erupting a melted slurry of substances such as water ice, nitrogen, ammonia, and methane.

New Horizons scientists stress the team's interpretation of these features as volcanoes is still tentative.

"These are big mountains with a large hole in their summit, and on Earth that generally means one thing — a volcano," said Dr Oliver White, a scientist with NASA's Ames Research Centre at Moffett Field, California.

If they are volcanic, then the summit depression would likely have formed through the collapse of the overlying surface as material erupted from underneath.

The strange hummocky texture of the mountain flanks are thought to be volcanic flows that have travelled down from the summit onto the plains beyond.

The discovery of recently active volcanoes on Pluto would raise important questions about the dwarf planet's geological and atmospheric evolution.

Scientists are trying to determine what is generating the heat needed to allow recent geologic activity to occur on Pluto.

Although Pluto and its largest moon, Charon, orbit each other as a binary system, scientists calculate the gravitational tidal forces each imposes on the other is not strong enough to cause internal ices to melt and erupt.

They now suspect the decay of naturally occurring radioactive elements in Pluto's core may be the heat source for the dwarf planet's continued geologic activity.

Evidence of cryovolcanism has been seen on other worlds throughout the solar system, including the tiger stripe geysers of Saturnian moon Enceladus and the nitrogen volcanoes of Neptune's moon Triton.

New Horizons became the first probe to visit the Pluto system on July 14.

The spacecraft has just completed a course adjustment to place it on a trajectory to intercept another frozen Kuiper Belt object — known as 2014 MU69 — in early January 2019.