If you are planning a visit to the Arctic Circle, one of the most common and memorable sights along the way will be glaciers and icebergs. These dense formations of ice are ever-present in both water and along land, formed by consistently frigid temperatures and snowfall over thousands of years. In addition to their natural beauty, they also form an integral part of the Arctic’s ecosystem, with a number of animal species using them for shelter.

While both are composed of ice, glaciers and icebergs are very different. Here’s a guide to glaciers and icebergs in the Arctic Circle: how they work, where they came from, and what their future is in a world affected by climate change.

Glaciers and Icebergs in the Arctic Circle

Glaciers are defined as persistent large bodies of ice that slowly move, propelled by their own weight. While commonly associated with the Arctic Circle and Antarctica—indeed, 99 percent of all glaciers are located in these two regions—glaciers can be found on every continent, usually in high mountain ranges such as the Himalayas, Andes, and the Southern Alps of New Zealand. The vast bulk of glaciers in the polar regions are contained within “ice sheets,” large glacial formations that can cover entire landmasses; for example, 98 percent of Antarctica is covered by an ice sheet.

Glaciers form when snow accumulation exceeds melting and sublimation over a period of centuries. In more temperate regions of the world, such as the continental United States, snow typically melts due to seasonal temperature changes, preventing the formation of glaciers. However, in the polar regions and on high mountaintops, consistently frigid temperatures result in snow accumulating faster than it can melt. This gradual process eventually results in the creation of a glacier, as newer snow compacts and buries older snowfalls, crystallizing them into pure ice. In some areas of the Arctic and Antarctica, such as Banks Island in northern Canada, glaciers cannot form due to a lack of snowfall; these areas are known as “polar deserts.”

Scientists classify glaciers into several types based on their size, shape, and location. Glaciers that form in mountainous regions are referred to as “alpine glaciers,” while glaciers that form within valleys are referred to as “valley glaciers.” Glaciers less than 50,000 square kilometers (19,000 square miles) are referred to as “ice caps,” while glaciers that exceed this size are known as “ice fields” or “ice sheets.” The only ice sheets remaining in the world are the ones that cover much of Antarctica and Greenland. Finally, glaciers that extend into the ocean are known as “tidewater glaciers” or “ice shelves.”

Glaciers are often noted for their color, which is typically a deep blue. This is due to the fact that water, whether frozen or liquid, absorbs blue light less efficiently than other colors of light. This is also why lakes, rivers, and oceans also appear blue. While ice cubes and other small quantities of ice typically appear white, glaciers rarely do because they lack air bubbles, which are responsible for giving ice its white appearance.

Despite their static appearance, glaciers are in fact constantly moving due to gravity, chemical changes in their surroundings, and the Earth’s own natural movements. Ice that is thicker than 50 meters loses its ability to act as a consistent solid due to constant pressure on different levels, with this pressure causing movement. Due to varying levels of heat and molecular actions in different parts of a glacier, parts of it may move faster than others; fast-moving parts of a glacier are often referred to as “ice streams.” Glacial movement typically results in the formation of crevasses and other geographic features.

Due to their size, glacial movement typically results in severe erosion of the lands on which they rest. During the last Ice Age, much of North America was covered by glaciers, whose constant movement and subsequent retreat caused permanent changes in the continent’s geography, many of which are visible today. This is most notably seen in the American Midwest, where glacial movement flattened the terrain; a notable exception to this is the Driftless Area in southwestern Wisconsin, southeastern Minnesota, northeastern Iowa, and northwestern Illinois, which was largely uncovered by glaciers and retains its unique hilly geography.

Due to the fact that they are created by snowfall, glaciers are primarily composed of fresh water, and are the largest reserve of clean, fresh water on Earth. Glacial retreat caused by global warming has become a problem in recent decades, as melting glacial ice results in rising sea levels, threatening low-lying coastal regions across the planet.

Notable glaciers in Alaska include the Mendenhall Glacier, Hubbard Glacier, and Exit Glacier, many of which have become tourist attractions. Glaciers also form an important part of the Arctic and Antarctic ecosystems, as many species, most notably polar bears, live on them. The breakup and retreat of glaciers caused by climate change threatens the existence of a large number of polar species.

Icebergs are much smaller ice formations created when a portion of glacial ice breaks free and lands in the ocean, a process referred to as “calving.” Due to their freshwater composition, icebergs have a slightly lower density than sea water, resulting in only a small portion of the iceberg’s mass being visible above the water. This phenomenon is the source of the colloquial phrase “tip of the iceberg.” Icebergs typically appear white due to snowfall, but can also appear blue, green, yellow, or many other colors.

Ocean currents typically result in icebergs either migrating close to shorelines, where they typically form larger groupings known as “pack ice,” or migrating out into the open sea, where they generally slowly melt due to changing temperatures and chemical decomposition caused by interaction with salt water. Melting icebergs create a fizzling sound known as the “Bergie Seltzer,” caused by trapped air bubbles within the ice becoming exposed to the open air.

Icebergs form in different shapes depending on where they are calved. Most icebergs are generated by calving along the edges of ice sheets in Greenland or Antarctica. Greenlandic icebergs tend to have irregular shapes, while Antarctic icebergs form large tabletop shapes. Due to more extreme climate conditions in the Antarctic, the largest observed icebergs have been witnessed there. The largest iceberg on record, Iceberg B-15, was formed after calving from the Ross Ice Shelf in Antarctica in 2000; it measured 183 miles (295 kilometers) in length and 23 miles (37 kilometers) in width before it broke up later in the year.

Icebergs are regarded as a major maritime hazard due to the fact that ships cannot easily see their full size because most of it is underwater, resulting in collisions that can heavily damage or sink a ship. Following the formation of the Russian Empire in 1721 by Peter the Great, an overarching goal of the Russian government was to develop an ice-free port that would allow them to trade year-round, as their existing ports were closed off much of the year due to the threat of icebergs.

Perhaps the most famous iceberg-related maritime disaster was the sinking of the RMS Titanic in 1912. Touted by her builders and owners as “unsinkable,” the Titanic was journeying from southern England to New York City when she hit an iceberg roughly 600 kilometers (375 miles) south of Newfoundland. The collision resulted in hull plates along the Titanic’s starboard (right) side buckling, allowing water to flood the lower decks of the ship. Of the more than 2,200 passengers and crew aboard the Titanic, 1,500 died in the subsequent sinking, and the subsequent outcry led to the formation of the International Ice Patrol, a transnational organization that monitors iceberg activity in the Arctic and Antarctic regions.

Conclusion

Glaciers and icebergs, despite their danger, remain some of the most popular sights in the Arctic and Antarctic regions. Their massive size, unique geographical features, and abundance of wildlife make for memorable sights no matter the time of year. There are many national parks and cruise ship tours where you can witness glaciers or icebergs in a safe environment, ensuring that your Arctic adventure is one of the most memorable you’ll ever take.