Types of Ice: Sea Ice, Glacial Ice, Icebergs & Permafrost

The 5 main types of ice are: sea ice (frozen seawater), glacial ice (compacted snow on land), icebergs (chunks broken from glaciers), ice shelves (floating extensions of glaciers), and permafrost (permanently frozen ground). Each type forms through different processes and plays a unique role in Earth's climate.

Ice exists in many forms on Earth, from floating sea ice to ancient glacial ice and frozen ground (permafrost). Each type plays a distinct role in Earth's climate system.

Sea Ice

Sea ice forms when ocean water freezes, typically at about -1.8°C (saltwater freezes at a lower temperature than freshwater). It is relatively thin (1-3 meters for first-year ice, 3-5 meters for multi-year ice) and floats because ice is less dense than liquid water. Sea ice coverage fluctuates seasonally — Arctic sea ice reaches its minimum in September and maximum in March.

How it forms: Ocean surface water cools below its freezing point (-1.8°C). Ice crystals form, creating "frazil ice" that consolidates into sheets. Salt is excluded during freezing, making sea ice relatively fresh.

Examples: Arctic Ocean sea ice, Antarctic sea ice belt, frozen Baltic Sea in winter

Glacial Ice

Glacial ice forms on land from the compression of accumulated snow over decades to millennia. Fresh snow compacts into granular firn, then into dense glacial ice under pressure. Glacial ice can be thousands of meters thick and millions of years old. It stores about 69% of Earth's freshwater and holds records of past climates in trapped air bubbles.

How it forms: Snow accumulates in regions where annual snowfall exceeds annual melting. Over decades, snow compresses into firn (granular ice), and further compression transforms it into solid glacial ice.

Examples: Antarctic Ice Sheet, Greenland Ice Sheet, alpine glaciers worldwide

Icebergs

Icebergs are large chunks of glacial ice that break off (calve) from glaciers or ice shelves and float in the ocean. About 90% of an iceberg is below the waterline. They can be enormous — the largest recorded iceberg (B-15) was 295 km long. Icebergs gradually melt as they drift into warmer waters.

How it forms: Glaciers or ice shelves reach the coast and extend over the water. Tidal action, waves, and the weight of the ice cause chunks to break off (calving), creating icebergs.

Examples: Antarctic tabular icebergs, Greenland icebergs (including the one that sank the Titanic), Iceberg B-15

Ice Shelves

Ice shelves are thick platforms of ice that form where glaciers or ice sheets flow to the coast and extend over the sea. They float on the ocean but remain attached to the land ice. Ice shelves act as "buttresses" that slow the flow of ice from land to sea. Their collapse accelerates ice loss and sea-level rise.

How it forms: Land-based glaciers flow to the coast and extend over the ocean. Fed by snowfall on top and freezing of seawater underneath, they can grow hundreds of meters thick.

Examples: Ross Ice Shelf (Antarctica, size of France), Ronne-Filchner Ice Shelf, Larsen Ice Shelf (partially collapsed)

Permafrost

Permafrost is ground that remains frozen (below 0°C) for at least two consecutive years. It can extend hundreds of meters deep and covers about 25% of the Northern Hemisphere's land surface. Permafrost stores massive amounts of carbon — about twice what is currently in the atmosphere — and its thawing is a major climate concern.

How it forms: In regions where the mean annual temperature is below freezing, the ground stays frozen year-round, even though the surface layer (active layer) may thaw in summer. Permafrost has been accumulating for thousands of years.

Examples: Siberian permafrost, Alaskan permafrost, Canadian Arctic permafrost, Tibetan Plateau permafrost

Frost and Ground Ice

Ground ice includes various forms of ice within frozen soil — ice lenses, ice wedges, massive ice bodies, and pingo ice cores. These features shape permafrost landscapes, creating pingos (ice-cored hills), thermokarst lakes (formed by thawing), and patterned ground (polygonal cracks). Surface frost includes hoar frost and rime ice.

How it forms: Water in soil freezes and expands, creating ice structures. Repeated freeze-thaw cycles over thousands of years build up complex ground ice features. Thermal contraction cracks fill with water that freezes into ice wedges.

Examples: Pingos (Tuktoyaktuk, Canada), ice wedge polygons, thermokarst lakes across Siberia

Key Facts

• About 10% of Earth's land surface is covered by glacial ice.
• Arctic sea ice has declined by about 13% per decade since satellite measurements began in 1979.
• If all glacial ice melted, global sea level would rise about 70 meters.
• Permafrost contains an estimated 1,500 billion tonnes of carbon — a "carbon time bomb" if it thaws rapidly.

Fun Facts

• Ice cores from Antarctica contain air bubbles up to 800,000 years old, providing a record of ancient atmospheres.
• The Titanic was sunk by a Greenland iceberg that had calved off a glacier 2-3 years before the collision.
• Lake Vostok in Antarctica lies beneath 4 km of ice and has been sealed off for at least 15 million years.

Summary

Earth's cryosphere — its frozen water — plays a critical role in climate regulation, sea-level control, and carbon storage. Understanding the different types of ice is essential for predicting how our planet will respond to ongoing warming.