What are glaciers? How are glaciers formed? Types of Glaciers - Glaciers explained

What are glaciers? Glaciers are massive, ancient ice formations that shape mountains, preserve valuable information about Earth's history within their frozen layers, and even reshape entire landscapes as they move.

This post is all about glaciers. We’ll learn what glaciers are, how glaciers are formed, and we'll also explore the different types of glaciers we can find across the globe. And finally, I will clarify what is the difference between a glacier and an iceberg.

What are glaciers?

Glaciers are massive, persistent bodies of ice that are located on land and last year-round. Covering about 10% of Earth’s surface, glaciers are not just frozen giants—they’re powerful forces of nature that carve and shape the landscape through their gradual movement.

Glaciers usually form in high-altitude mountain regions where it’s both cold and snowy, but we can also find them in low-lying, constantly freezing areas like Greenland and Antarctica.

How are glaciers formed?

The process of glacier formation starts with the annual snowfall. When snow builds up year after year without melting away completely in the summer, it leads to the accumulation of layers upon layers of ice, eventually creating the dense ice masses known as glaciers. The snow that persists throughout the entire year is called perennial snow, and it forms a snow field when a thin layer accumulates.

As time passes, the older snow that has accumulated from previous seasons, which is referred to as névé, is gradually compacted, eventually transforming into firn—a dense, granular mass of ice crystals.

As even more snow accumulates, it further compacts the firn by pushing together thee ice granules and squeezing out most of the air that used to be between them. This reduces the porosity of the fern and creates a denser ice mass—the glacial ice. Although dense, solid glacial ice still contains some tiny bubbles of air. These tiny pockets of air offer a glimpse into past eras and providing scientists a unique opportunity to study the past compositions of our planet's atmosphere.

Types of glaciers

There are two main types of glaciers: continental glaciers and alpine glaciers. These, can then be further subdivided into subcategories based on their size, location, and form. From towering mountain ice rivers to massive ice sheets covering entire continents, each type of glacier has its own story to tell.

Continental glaciers

These colossal ice masses cover the Earth's polar regions, mainly Antarctica and Greenland, where the temperatures are always so low that they prevent the snow from melting completely. Over time, this snow accumulates into extremely thick ice formations, reaching thousands of meters in depth. Because continental glaciers cover such vast, often flat expanses, their ice spreads outward from the thickest central regions toward thinner edges, a pattern differing from the downhill flow of alpine glaciers.

Antarctica and Greenland house Earth's two biggest continental glaciers, containing roughly 99% of the planet's glacial ice and about 68% of its freshwater. If they were to ever completely melt, that would cause sea levels to rise by about 80 meters, radically reshaping global coastlines, submerging many major cities. This is why we have to do everything we can to significantly slow down or even reverse the rate of global warming by taking global action against climate change.

Ice sheets

Greenland ice sheet - continental glacier

Ice sheets are the largest category of continental glaciers—covering more than 50,000 square kilometers and may be as deep as several thousand meters. These immense structures form domes of ice at their highest points and spread out in all directions.

At almost 14 million square kilometers, the Antarctic ice sheet is the largest one, and it spans over nearly the entire Antarctic continent. In the Northern Hemisphere, the largest ice mass is the Greenland’s ice sheet, its roughly 1.7 million square kilometers covering 80% of the island.

With constant, but slow, outward flow, ice sheets reshape the land beneath them and have a profound effect on global sea levels.

Ice caps

A smaller type of continental glacier is the ice cap. Similar to ice sheets, they also form dome-shaped structures, but they are smaller in size compared to the ice caps. Think of ice caps as the smaller “cousins” of ice sheets—covering less than 50,000 square kilometers, usually found in high-latitude polar and subpolar mountain regions.

We can find ice caps in various locations, including Iceland, the Svalbard archipelago of Norway, and several mountain ranges in the United States.

Alpine glaciers

Mer de Glace Alpine glacier, Chamonix

Alpine glaciers are characterized as slow-moving rivers of ice that form high in mountain regions where snow persists throughout the year. They can form in polar, temperate, or even tropical regions, as long as the altitude is high enough and the temperature low enough to ensure a constant layer of ice.

Alpine glaciers can be found inching their way down the slopes of mountain ranges such as the Andes, Rockies, Alps, and Himalayas, often squeezing through long, narrow valleys. If an alpine glacier flows down a valley, it is called a valley glacier.

Sometimes alpine glaciers can form even at lower elevations, provided there’s enough snowfall year-round, as is the case in Washington’s Olympic Peninsula.

What is the difference between a glacier and an iceberg?

We've seen that a glacier is a massive, long-lasting body of ice that sits on land and moves very slowly under its own weight. These frozen giants form in cold regions where snowfall outpaces melting, causing layer upon layer of snow to compact into ice over many years.

Iceberg freely floating in the ocean

By contrast, an iceberg is a chunk of ice that has broken off—calved—from an alpine glacier or an ice sheet and now floats freely in a lake or the ocean. While glaciers typically remain anchored to land, icebergs drift with currents and winds, revealing only a fraction of their bulk above the water’s surface. The term "Iceberg" literally means "ice mountain," with "berg" being the German word for mountain.

Have you ever seen a glacier or an iceberg in person? I was lucky enough to see both during my adventures in Greenland and they’re some of the most breathtaking natural wonders I’ve ever experienced. I was, and still am, fascinated by the Ilulissat ice fjord (one of our planet's natural heritage sites), a sight so unforgettable, it’s etched in my memory for good.