A new hydrothermal vent field -- which scientists have dubbed `The Lost City' -- was discovered recently on an undersea mountain southeast of Bermuda.

The discovery was made at 30 degrees north on the Mid-Atlantic Ridge during an oceanographic cruise aboard the research vessel Atlantis .

Bermuda is located at roughly 32 degrees north and the mid Atlantic Range, where the vents are located, is roughly 1,500 miles to the east.

A team of scientists from the Scripps Institution of Oceanography, Duke University, The University of Washington and other institutions conducted the National Science Foundation (NSF) supported expedition.

The structures tower 180 feet above the seafloor and are the largest hydrothermal chimneys of their kind ever observed.

Surprising for undersea vents is the fact that the venting structures are composed of carbonate minerals and silica, in contrast to most other mid-ocean ridge hot spring deposits which are formed by iron and sulphur-based minerals.

Researchers have said that the low temperature hydrothermal fluids may have unusual chemistries because they emanate from mantle rocks.

Scientists believe these vents are unique because they rest on one-million-year-old ocean crust formed tens of kilometres beneath the sea floor, and because of their incredible size.

Dense macrofaunal communities such as clams, shrimps, mussels and tube-worms which typify most other mid-ocean ridge hydrothermal environments appear to be absent in this field.

The vents were discovered unexpectedly while studying geological and hydrothermal processes that built an unusually tall 12,000 foot mountain at this site.

Observations using the submersible Alvin, and deep towed vehicle, Argo, operated by Woods Hole Oceanographic institution, show that the field hosts numerous active and inactive hydrothermal vents.

The steep-sided 180 foot tall deposits are composed of multiple spires that reach 30 feet in width at their tops.

They are commonly capped by white, feathery hydrothermal precipitates, and the tops and sides of the massive edifices are awash in fluids that reach temperatures up to 160 degrees.

From the sides of the structures, abundant arrays of delicate white flanges emerge and similar to cave deposits, complex intergrown stalagmites rise several metres above the flange roofs.

Underneath the flanges, trapped pools of warm fluid support dense mats of microbial communities that wave within the rising fluids.

Downslope, hundreds of overlapping flanges form hydrothermal deposits reminiscent of hot spring deposits in Yellowstone National Park.

During the Alvin dive, expedition leader Patrick Hickey collected rocks, fluids, and biological samples for shore based analysis.