A vast hole in the Earth on the same scale as the Grand Canyon lies buried under ice in Greenland, scientists have learned.
The hidden mega-canyon is at least 466 miles (740km) long and up to 2,624ft (800m) deep in places.
The feature, resembling a meandering river channel, is believed to pre-date the ice sheet that has covered Greenland for millions of years.
Professor Jonathan Bamber, from the school of geographical studies at University of Bristol, said:
"With Google Streetview available for many cities around the world and digital maps for everything from population density to happiness, one might assume that the landscape of the Earth has been fully explored and mapped.
"Our research shows there's still a lot left to discover."
The canyon was uncovered by airborne radar which can penetrate ice and bounce off the land beneath.
The British man who died during a charity trek across the Greenland ice cap was trapped in a severe snow storm for around 30 hours before emergency teams could reach him and his two friends.
Philip Goodeve-Docker, an events manager, along with expedition leader Roan Hackney and Andy Norman, a former IT professional, got into difficulty when the sudden storm hit. Mr Goodeve-Docker died before the team could be airlifted to safety.
Temperatures in Greenland dropped to as low as minus 10.5C (13F) on Saturday, while gusts of 95 miles (152km) an hour were reported on the east coast. Both Mr Hackney and Mr Norman remain in a "critical condition" in hospital, according to Mr Goodeve-Docker's brother, Mark.
Philip Goodeve-Docker and his team mate Andy Norman were both "rookies to the Arctic" according to Mr Norman.
Writing on his website before the trip, the 33-year-old former IT professional said he was "setting foot for the first time in the Arctic Circle" and described Mr Goodeve-Docker as "completely new to the Arctic and indeed this adventure lark" but added that his friend had been "training furiously".
Mr Norman and Mr Goodeve-Docker undertook the unsupported crossing with experienced expedition leader Roan Hackney.
The trio was supported and monitored during the trip from the UK, managed by a world leader in managing Greenland expeditions.
Well-wishers continued to pledge donations to Philip Goodeve-Docker's nominated charity today in tribute to the adventurer.
Mr. Goodeve-Docker died on Sunday after he and his friends Andy Norman and Roan Hackney attempted to cross the world's second largest icecap unsupported.
He undertook the challenge in a bid to raise more than £5,000 for the The Queen's Nursing Institute.
Writing on his Just Giving page this morning, one contributor wrote: "Would have paid any money to have you back my friend still can't believe you are gone. rest in peace hope to see you again one day."
Another wrote: "In memory, you made a difference and lived large!!"
A Foreign Office spokeswoman said it is providing assistance to relatives of Philip Goodeve-Docker and to the families of the two rescued men from his party.
We are aware that British nationals were in difficulty during an expedition in Greenland and have been rescued by the authorities. Sadly one of the men, Philip Goodeve-Docker, died. The two other British nationals are in hospital.
We are providing consular assistance to their families at this time.
Philip Goodeve-Docker undertook a charity trek across the Arctic in tribute to his late grandfather, according to his Just Giving page.
The 30-year-old charity promoter described the 550-600km trek as "one of the great polar challenges."
This is one of the great polar challenges, through which we face such dangers as polar bears (not cute and cuddly), crevasses up to 500 metres deep, polar winds, temperatures of 5C to -50C, plus the horror of 3 men with one tent & no washing.
Part of my reasons for this frankly nutty adventure is my Grandfather, Patrick Pirie-Gordon, who passed away two years ago. Amongst his achievements were his key roles as Treasurer and Honourary Vice-President for the Royal Geographical Society, helping fund polar exploration, and Treasurer for the QNI.