Submarine crews practice surfacing the 8, 000-ton submarines, directly through thick ice or in nearby open waters, and learn to avoid hitting another ship.
But since the 1960s, satellites and aircraft with powerful radar devices have discovered more and more lakes buried kilometres beneath the thick ice sheet.
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Working at a speed of two knots, HMS Protector broke the four-metre thick ice, which had trapped the cruise ship's bow, in two hours.
When I sailed through the passage on a Canadian icebreaker, the Amundsen, in October that year, we encountered huge floes of thick ice.
That's a lot for a boat that might sit in the shed for years at a time, waiting for the right conditions of smooth, thick ice.
Singstad said he and others tied a rope to her feet and tried unsuccessfully to pull her free, and the snow shovel and small saw they had brought were no match for the thick ice.
Once at the motor sports complex, journalists took turns testing all-wheel-drive XJs and smaller XFs, which also get the system as an option for 2013, by flinging them through various obstacle courses, every one of which was covered in several inches of snow with thick ice underneath.
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Only her skis and Telemark boots and bindings protruded from the thick, opaque ice.
The situation wasn't much better in many Long Island communities, where commuters woke up Monday to roads jammed with thick layers of ice and slush.
The oil is so thick on the surface that ice from nearby Columbia glacier turned black.
It's an inky blue body of water thick with floating, ancient ice.
The ice was so thick and clean and glimmery that the fish and errant golf balls were happy to be frozen in it.
When the ice sheets were thick and advancing, more pebbles, stones, and dirty sediment would have been carried into the core by the moving ice.
To the casual reader, the shrinking area of white seemed to signify disappearing ice, so the graphic may have given a totally misleading impression that Greenland had become ice-free - even where the ice is 3km thick.
The Dakotas, frozen thick for weeks, sent an ice wind east for the occasion, but it thawed a bit by Monday.
The Elfstedentocht takes place anytime the weather is cold enough that the canals connecting 11 cities in the province form a thick and relatively unbroken sheet of ice.
It has an average elevation of 3, 000 m (9, 900 ft) and the ice is typically 4 km thick.
During glacial ages that exist about 90% of the time, our Northern Hemisphere is mostly covered with ice up to several miles thick.
Still, that ice mass was about 16 inches thick Monday, and the weather can change quickly in Minnesota.
From a research station operated by the National Science Foundation called Summit Camp, a spot where the ice sheet is about 2 miles thick, GROVER will crawl at an average speed of 1.2 mph (2 kilometers per hour).
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Most of Greenland is covered by a sheet of ice that averages more than a mile thick.
Today, however, a range of newly popular active sports are reinvigorating the former battlefields, as travellers discover a world of ice-blue rivers, rugged hills and thick forests, which unfurls south from Karlovac to meet the vertiginous Velebit mountains that rise up towards the coast.
But further measurements using a laser and looking for reflections showed that much of the ice is covered with a layer of dark material tens of centimetres thick.
The high point of the journey came on the second afternoon of the trip, as the ferry approached the incredible ice walls of the Patagonian glaciers, entering a turquoise-tinted bay thick with floating icebergs.
Assuming that climate history over the past 400, 000 years continues to repeat its pattern with the nearly electrocardiogram regularity, maybe we should think about enjoying this brief intermission before the next life-unfriendly Ice Age covers much of the Northern Hemisphere with glaciers up to miles thick for the next 90, 000 years.
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Arctic sea ice is usually 1 to 3 meters, or as much as 9 feet thick.
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And you will pass a golf course, and see four hackers out there dressed for ice fishing, moving slowly, knocking a fluorescent orange ball across a fairway thick with snow.
About 14 million years ago, a period of climate change caused the formation of the Antarctic ice sheet, which averages one mile in thickness and gets up to three miles thick in some parts.
Depending on the capricious whims of the extreme Arctic climate and calendar, thick clouds reveal remote fragments of the landscape as if concealing some great mystery, blinding sunshine illuminates the ice, or perpetual moonlight bathes it all in the strange, blue half-light of the polar night.
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