Encyclopedic Entry

Ice is frozen water.

Photograph by Michaela Murray, My Shot

Bose-Einstein Condensate
Ice is cold, but its not the coldest state possible. There is a strange, fourth state of matter (added to the familiar list of liquid, solid, and gas) called Bose-Einstein condensate that occurs when atoms approach absolute zero, the temperature at which all atomic motion stops. When this happens, atoms lose their individual properties and meld into a single "superatom." Bose-Einstein condensate behaves strangely and physicists are still studying it.

Bose-Einstein condensate is not observable in nature on Earth, because no temperatures on Earthnot even near the polesapproach anything near absolute zero.

Ice is water in its frozen, solid form. Ice often forms on lakes, rivers and the ocean in cold weather. It can be very thick or very thin. It occurs as frost, snow, sleet and hail.

Water will freeze at zero degrees Celsius (32 degrees Fahrenheit). Once it gets close to its freezing point, water molecules begin to expand. In a small space, these expanding molecules can create a lot of pressure. This is why freezing water can burst even the heaviest of metal pipes in the winter. This is also the reason your ice tray at home can look like its overflowing with ice, even though you only filled it halfway with water. If water freezes in a crack in rock, the ice can eventually break the rock apart. Because of these powerful properties, ice is very important in the processes of weathering, where rocks are broken into smaller bits, and erosion, where rocks and earth are washed or moved to other locations.

The expanded molecules make ice a lot lighter than liquid water, which is why ice floats. An iceberg that weighs several tons can still float easily in the ocean, just like a piece of ice floats easily in your cup of water or soda.

Water covers more than 70 percent of the Earths surface. Slightly more than two percent of the Earths water is frozen into ice; almost all of this ice is in glaciers, which are huge masses of ice. Today, glaciers are found in many mountainous areas and in the polar regions of the Earth.

Ice Sheets

Glaciers that cover more than 50,000 square kilometers of land are called ice sheets. The North and South Poles of the Earth are covered with ice sheets. In fact, almost the entire continent of Antarctica is covered with ice. The Antarctic Ice Sheet is about the size of the United States and Mexico combined. The Greenland Ice Sheet near the North Pole is three times the size of Texas. During past ice ages, continental ice sheets like the ones at the poles covered huge portions of North America and Europe.

Large areas covered with ice that are less than 50,000 square kilometers are called ice fields.

Sea Ice

Frozen ocean water is called sea ice. While icebergs form on land and then break off into the sea, sea ice forms in the ocean. Ice that has survived one melt season is called old ice. Every fall, large sections of northeastern Canadas Hudson Bay freeze over. Polar bears hunt for seals under the cover of the Hudson Bays old sea ice. When the ice melts in spring, the polar bears return to land. They eat very little until the ocean freezes again in the fall.

Mobile sea ice that floats freely in the ocean, not attached to any shoreline, is called drift ice. There are many different kinds of drift ice. A collection of icebergs and ice no more than 2 meters (6.5 feet) wide, for instance, is called brash ice.

Frazil ice is a thin layer of freshwater crystals formed as ice interacts with the surface of the ocean. Frazil also forms through cold, quickly flowing streams.

Grease ice is a thin accumulation of frazil. Grease ice is thicker than frazil, but not solid enough to be a true iceberg or ice floe. Grease ice makes the ocean look somewhat like an oil slick. A thin, frozen layer of grease ice is called an ice rind. A slushy, spongy collection of grease ice is called shuga.

Frazil and grease ice create nilas ice, which is newly formed and usually transparent. Sometimes, nilas ice and various ages of old ice freeze together, forming breccia ice.

Unlike drift ice, fast ice is attached to the shore or sea floor, and it doesnt move with the wind or currents. A large area of accumulated drift ice is called pack ice. An ice floe is a floating chunk of ice that is less than 10 kilometers wide.

Black Ice

When water hits a cold road and quickly freezes, a thin, clear layer of ice called black ice forms. Its called black ice because unlike snow, which is white, black ice is transparent, revealing the black road below.

Anchor Ice

In extremely turbulent conditions, water can drop below its freezing point without actually freezing solid. Under these conditions, tiny individual ice crystals form, creating a slushy mixture. These slushy pieces of ice can build up and stick to the bottom of rivers or oceans, becoming anchor ice.

Dry Ice

Frozen carbon dioxide, called dry ice, is unique because it melts directly into a gas, skipping the liquid stage. With a temperature measuring over 100 degrees below zero (Fahrenheit), dry ice cools things very effectively, but can also pose a danger. Touching dry ice can cause frostbite.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

anchor ice

Noun

ice crystals built up at the bottom of a lake bed, river bed, or sea floor.

Antarctic Ice Sheet

Noun

thick glacier covering most of Antarctica.

black ice

Noun

water that has quickly frozen over a paved road, forming a transparent sheet of ice.

brash ice

Noun

floating fragments of ice and icebergs no more than 2 meters (6.5 feet) across.

breccia ice

Noun

ice, usually sea ice, of different ages frozen together.

carbon dioxide

Noun

greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.

Celsius scale

Noun

scale for measuring surface temperature, used by most of the world, in which the boiling point of water is 100 degrees.

drift ice

Noun

sea ice that floats freely in the ocean, not attached to a shoreline.

dry ice

Noun

frozen form of carbon dioxide.

erosion

Noun

act in which earth is worn away, often by water, wind, or ice.

Encyclopedic Entry: erosion

Fahrenheit scale

Noun

scale for measuring surface temperature used by Belize, Liberia, Myanmar, and the United States.

fast ice

Noun

sea ice that is attached to a shoreline or the seafloor.

frazil

Noun

ice crystals or thin plates of ice that form in cold, turbulent water.

frost

Noun

thin coat of ice covering objects when the dew point is below freezing.

Encyclopedic Entry: frost

gas

Noun

state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

glacier

Noun

mass of ice that moves slowly over land.

Encyclopedic Entry: glacier

grease ice

Noun

thin layer of ice crystals (frazil) clumped together.

hail

Noun

precipitation that falls as ice.

Encyclopedic Entry: hail

ice age

Noun

long period of cold climate where glaciers cover large parts of the Earth. The last ice age peaked about 20,000 years ago. Also called glacial age.

iceberg

Noun

large chunks of ice that break off from glaciers and float in the ocean.

Encyclopedic Entry: iceberg

ice field

Noun

area of fewer than 50,000 square kilometers (19,000 square miles) covered by interconnected ice caps.

ice floe

Noun

floating chunk of frozen water less than 10 kilometers (6.2 miles) wide.

ice rind

Noun

thin, brittle crust of ice formed on a calm body of water.

ice sheet

Noun

thick layer of glacial ice that covers a large area of land.

Encyclopedic Entry: ice sheet

liquid

Noun

state of matter with no fixed shape and molecules that remain loosely bound with each other.

molecule

Noun

smallest physical unit of a substance, consisting of two or more atoms linked together.

nilas

Noun

newly created, still-transparent sea ice.

old ice

Noun

icebergs or sea ice that has survived more than one melt season.

pack ice

Noun

large area of drift ice, or ice not attached to a shoreline.

polar

Adjective

having to do with the North and/or South Pole.

sea ice

Noun

frozen ocean water.

shuga

Noun

relatively small, spongy chunks of sea ice.

sleet

Noun

rain that freezes as it falls to Earth. Also called ice pellets.

Encyclopedic Entry: sleet

snow

Noun

precipitation made of ice crystals.

transparent

Adjective

invisible, or able to be seen through.

turbulent

Adjective

violent or chaotic.

weathering

Noun

the breaking down or dissolving of the Earth's surface rocks and minerals.

Encyclopedic Entry: weathering

For Further Exploration

Audio & Video

Credits

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Writers

Kim Rutledge
Melissa McDaniel
Diane Boudreau
Tara Ramroop
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrators

Tim Gunther
Mary Crooks, National Geographic Society

Editors

Kara West
Jeannie Evers

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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