Glaciers

Imagine you are trekking in the high Himalayas. As you ascend, the air gets colder, the terrain turns from lush green to rocky, and finally, you reach a point where snow never melts. This is the snow line—the altitude above which temperatures never rise above freezing, even in the hottest month of the year. So, we can define snow line as:

Snow line denotes the height above which there is permanent snow cover because it corresponds to level where average temperature is always below the freezing point during even the warmest month of the year.

Now, imagine staying here for centuries. Every winter, fresh snow falls, layering itself over the previous deposits. With time, the weight of the upper layers compresses the snow below, squeezing out air and turning it into a dense, glassy mass of ice. This is how a glacier is born—a mighty river of ice that moves slowly but persistently under the force of gravity.

About 10% of Earth’s surface is covered by glaciers today, but in the past, during Ice Ages, they spread over vast regions, shaping the very landscapes we see today.

Types of Glaciers

Just like rivers come in different forms—large and small, meandering and straight—glaciers too have various types, each shaped by its environment.

1. Ice Sheets / Ice Caps

If you were an astronaut looking at Earth from space, the most striking icy features would be the massive white expanses of Antarctica and Greenland. These are ice sheets, the largest glaciers on land, covering thousands of square kilometres. They are so vast that they appear like frozen continents themselves!

Think of an ice cap as a smaller version of an ice sheet, like a giant dome of ice sitting atop mountains or plateaus.

2. Continental Glaciers

When ice sheets expand and spread over most of a continent, they become continental glaciers. These glaciers once covered North America and Europe during Ice Ages, shaping entire landscapes by carving valleys and leaving behind massive deposits of rock and soil. Today, the Antarctic and Greenland ice sheets are the largest examples.

3. Mountain and Valley Glaciers

Imagine standing at the foot of the Himalayas, looking up at a white river snaking its way down between towering rock walls. This is a mountain or valley glacier, which flows like a slow-moving frozen river under the pull of gravity.

These glaciers originate in high-altitude regions and slowly creep down through valleys, shaping the mountains by eroding rocks and creating deep, U-shaped valleys. Some famous examples include the Gangotri Glacier in India and the Alaska glaciers in the US.

4. Piedmont Glaciers

Picture several valley glaciers flowing down from the mountains and merging at the foothills, spreading out like a pancake of ice. This is a piedmont glacier. It forms when multiple glaciers combine and fan out onto flat land.

A famous example is the Malaspina Glacier in Alaska, which looks like a frozen delta of ice.

5. Ice Shelves

Now, let’s travel to the polar regions. Here, glaciers extend beyond land and float over the ocean, forming ice shelves. These are thick, floating extensions of ice sheets that remain attached to the land but spread freely over water.

Antarctica’s Ross Ice Shelf is the world’s largest ice shelf—imagine an ice mass larger than France floating on the ocean! When chunks of these shelves break off, they form icebergs, which then drift across the seas.