Can you imagine relaxing on a ship in coastal waters with calm weather or only light winds and then being hit unexpectedly by hurricane force winds?It would be quite a surprise!Certain coastal areas in Antarctica can be calm for much of the time until hit by a katabatic wind.Before slamming into your ship, the air in that katabatic wind was at a higher elevation on the slope of a tall mountain or a high glacial valley.As that air cooled, it became denser than the air below it and began to “flow” down the mountain towards your unsuspecting vessel.For that reason katabatic winds are sometimes called down slope wind orfall winds.How strong can these winds be?Douglas Mawson, a famous Australian explorer, recorded frequent gusts of more than 150 miles per hour (240 kph) at his Cape Denison base in 1912.

If you’re thinking about exploring Antarctica, however, the occasional katabatic winds aren’t the only winds that should concern you.Antarctica is the windiest of the continents and some coastal areas endure almost constant strong winds.Over the two years Mawson spent recording wind speeds at Cape Denison, the average wind speed was 45 mph (72 kph).

Why is Antarctica so windy?In addition to global wind currents, Antarctica creates its own wind systems.Cold air slides down the ice plateau, gaining speed as it leaves the high interior ice fields and descends to the lower areas near the coasts.These winds can form impressive clouds of blowing snow that reach high into the air.Winds this strong, combined with cold temperatures, would quickly freeze any human’s exposed skin.

Visualize a mountain range that is more than 800 miles (1300 km) long and 9,900 feet (3,000 meters) high. That’s twice as long as California’s Sierra Nevada and eight times higher than the Empire State Building. Now imagine it completely covered by an ice plateau—you could walk right over the top of this mountain range without even knowing it was there! You would need a lot of ice to cover a mountain range that big. This isn’t just an imaginary mountain range, however, it exists in Antarctica and is covered completely with ice. There are also several other massive mountain ranges in Antarctica with only isolated peaks and rock cliffs poking out from the ice dome that covers most of Antarctica. In some places in Antarctica the ice is more than 13,200 ft (4,000 meters) thick. That’s two and a half miles deep, or more than ten and a half times taller than the Empire State Building.

How much ice is on Antarctica? The Antarctic Ice Cap contains about 85% of the world’s ice, which is about 80% of all the fresh water on earth. That ice weights about 27 million billion tons (24,500 million billion kg). It’s difficult to conceptualize a number that large. It might help to imagine 100,000 tons, the weight that could be carried by a container ship 335 meters long and 43 meters wide, one of the largest cargo ships on the ocean. If you loaded all the ice on Antarctica onto these cargo ships and then starting counting the ships, assuming you could count one ship per second, you would still be counting more than 860 years from now. The massive weight of the ice cap pushes the underlying continent about 3,300 feet (1,000 meters) into the earth’s crust.

If someone asked you to name the world’s driest continent, what would you guess? Would you be surprised to know it is Antarctica? Even though most of Antarctica is covered with ice and snow holding eighty percent of the world’s fresh water, the continent is, by definition, a desert. Antarctica accumulates on average fewer than 2 inches (5 cm) of water equivalent per year—that is just slightly more than what the Sahara Desert receives. You might wonder how, if Antarctica receives such a small amount of precipitation each year, it could accumulate eighty percent of the world’s fresh water. The snow and ice that forms the Antarctic Ice Cap accumulated over millions of years.

Imagine what it would be like if your house or apartment grew and shrank every year. In the Antarctic winter, sea ice more than doubles the surface area of Antarctica, giving expanded habitat for animals like penguins, seals, and seabirds. The winter sea ice can extend over 7.2 million square miles (19 million square kilometers) of ocean surrounding Antarctica, that’s an area of sea ice more than two times the size of the United States. In the Antarctic summer, much of the sea ice disappears and then reforms the next winter.

Animals who live on the sea ice and humans who travel across and through it must be able to “read” the changing ice and choose safe places to travel and rest. As surface water cools to the freezing point, ice crystals start to form. If the weather and sea conditions are calm, the ice crystals join together and thicken into young ice, a fibrous and weak ice you would want to try to avoid if you were out for a walk. Even a slight ocean swell can break the young ice into pieces that knock against each other, forming flat circular slabs of thin ice that look like pancakes and are called pancake ice. If it’s cold enough the pancakes will eventually freeze together and then freeze fast to the shore, forming fast ice.

Animals like penguins, seals, whales, and sea birds rely on waves, wind, tides and currents to buckle and crack the fast ice to allow access between the ocean water and the ice surface and to create breathing holes. Humans traveling across the sea ice try to avoid these leads of open water.

During normal summers, the fast ice breaks apart and forms floes, pieces of ice anywhere from 65 feet (20 meters) to 6 miles (10 km) across. The floes drift on the currents until they pack tightly together forming pack ice. Modern ice breaking ships can move through sea ice, but pack ice gave early explorers a lot of trouble—in 1915 Ernest Shackleton’s wooden ship The Endurance was trapped when the pack ice closed around it, holding it for ten months before crushing it as the spring thaw allowed giant floes to grind the ship between them.

In 1991 Will Steger’s international team of explorers spent weeks crossing the Larsen ice shelf on the eastern side of the Antarctic Peninsula. The team’s photographs from the Larsen show a flat plain of snow-covered ice extending to the horizon, similar to images from the salt flats. You would guess, looking at the photographs, the team members, their sleds and dogs were standing on solid ground. Below their feet, however, was approximately 720 feet (220 meters) of ice floating on top of the ocean.

How do shelves of ice form? As you might imagine, it’s a long process. First a cold spring season allows fast ice, a layer of sea ice that is frozen fast to the shore, to remain in place through the next year. Fast ice that survives more than one year is called bay ice. Bay ice that stays in place for many years is called shelf ice. Shelf ice gets thicker not only from freezing seawater, but also from snow and from glaciers moving towards the coasts. Ice shelves can be up to 1000 ft (300 m) thick. That’s almost a fifth of a mile thick.

While crossing the Larsen, the ice shelf felt very stable to Steger and his team. Scientists at Queen’s University estimate the shelf could have been stable for as long as 12,000 years—that many years ago there were still mastodons, mammoths, and saber-toothed cats roaming the earth. Over the course of three days in 2002, however, a chunk of ice the size of the New England state of Rhode Island broke free from the Larsen B ice shelf. The speed of the collapse surprised even the scientists who were monitoring the shelf. Scientists link the collapse with global climate change.