Encyclopedic Entry

Hardy plants can withstand frost.

Photograph by Giuliana Turi, MyShot

Don't Give These to Your Girlfriend
Frost flowers are formed when water in plant stems or trees oozes and freezes, sometimes in the shape of a flower. These types of "flowers" are rare, and when they do form, they're destroyed easily because they're so delicate.

Rime of the Ancient Mariner
The English poet Samuel Taylor Coleridge wrote a famous poem called The Rime of the Ancient Mariner, published in 1798. In the poem, an old sailor tells the story of how his ship lost its way in a storm, eventually ending up in the Antarctic. Coleridges title is a play on words. Much of the story takes place in the Antarctic, on a ship that is covered with rime. The mariners long, white beard is compared to hoarfrost. Finally, The Rime of the Ancient Mariner is written in rhyme.

Father Frost
The Russian Santa Claus is named Ded Moroz, or Father Frost.

Frost is water vapor, or water in gas form, that becomes solid. Frost usually forms on objects like cars, windows, and plants that are outside in air that is saturated, or filled, with moisture. Areas that have a lot of fog often have heavy frosts.

Frost forms when an outside surface cools past the dew point. The dew point is the point where the air gets so cold, the water vapor in the atmosphere turns into liquid. This liquid freezes. If it gets cold enough, little bits of ice, or frost, form. The ice is arranged in the form of ice crystals.

Frost is most common in low-lying areas. Warm air rises, and cool air sinks—cool air is denser than warm air. That means there are usually more water molecules in cool air than in warm air. As cool air collects in valleys, frost forms.

Frost usually forms at night, when the air temperature is cooler. Once the sun rises and warms the air around the frosted object, frost melts quickly.

Types of Frost

There are different types of frost. The most common are radiation frost (also called hoarfrost), advection frost, window frost, and rime.

Radiation frost is frost in the form of tiny ice crystals that usually shows up on the ground or exposed objects outside. Hoarfrost also forms in refrigerators and freezers.

Advection frost is a collection of small ice spikes. Advection frost forms when a cold wind blows over the branches of trees, poles, and other surfaces.

Window frost forms when a glass window is exposed to cold air outside and moist air inside. Window frost is familiar to winter residents of cold climates. Indoor heat and cold outdoor temperatures form this type of frost. Window frost was much more common before people began using double-paned windows.

Rime is frost that forms quickly, usually in very cold, wet climates. Rime also forms in windy weather. Rime sometimes looks like solid ice. Ships traveling through cold places like the Arctic Ocean often end up with rime covering at least part of the exposed part of the ship.

Frost and People

Frost can severely damage crops. It can destroy plants or fruits. Plants with thin skins, such as tomatoes, soy, or zucchini, can be ruined. If frost is bad enough, potatoes will freeze in the ground. Farmers have had entire fields destroyed in just a few frosty nights.

Farmers typically consult almanacs and maps to predict frost. Maps and information from almanacs (such as previous days of frost) tell farmers what areas usually receive frost, how often it occurs, and how long it lasts. These tools are reliable but are not always accurate.

Although farmers still rely on the weather, many spray their crops to reduce frost damage. This spray usually contains a genetically modified organism (GMO), an organism whose genes have been altered by people. The GMO that reduces frost damage to crops is called ice-minus bacteria. Ice-minus bacteria make it difficult for ice crystals to form. Ice-minus bacteria do no damage to the plant.

Many farmers also protect their crops by using the selective inverted sink (SIS) method. The selective inverted sink is a large fan that draws cold, moist air up into a chimney. The chimney expels the cold air far above the crops. This protects crops from frost without spraying them.

Sturdier plants are not destroyed by frost, but frost will stop them from growing. Evergreen trees, such as pine and spruce, will stop growing during a frost, but they won't die.

Roads can also be damaged by frost. Frosty roads are slippery and, exposed to the heat from cars, quickly become wet. Many drivers have trouble navigating frosty or wet roads.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

accurate

Adjective

exact.

advection frost

Noun

ice crystals shaped like spikes that form from a cold wind.

air

Noun

the layer of gases surrounding Earth.

Encyclopedic Entry: air

almanac

Noun

annual publication containing a calendar, astronomical information, and weather forecasts.

Antarctic

Noun

region at Earth's extreme south, encompassed by the Antarctic Circle.

Arctic Ocean

Noun

one of Earth's four oceans, bordered by Asia, Europe, and North America.

climate

Noun

all weather conditions for a given location over a period of time.

Encyclopedic Entry: climate

crop

Noun

agricultural produce.

Encyclopedic Entry: crop

delicate

Adjective

fragile or easily damaged.

dense

Adjective

having parts or molecules that are packed closely together.

dew point

Noun

temperature at which water in the air condenses to form water droplets on objects near the ground.

evergreen

Noun

tree that does not lose its leaves.

expel

Verb

to eject or force out.

farmer

Noun

person who cultivates land and raises crops.

fog

Noun

clouds at ground level.

Encyclopedic Entry: fog

freeze

Noun

weather pattern of temperatures below 0 degrees Celsius (32 degrees Fahrenheit).

frost

Noun

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

Encyclopedic Entry: frost

frost flower

Noun

ice crystals that form from moisture released by a plant stem or tree.

fruit

Noun

edible part of a plant that grows from a flower.

gas

Noun

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

gene

Noun

part of DNA that is the basic unit of heredity.

genetically modified organism (GMO)

Noun

living thing whose genes (DNA) have been altered for a specific purpose.

glass

Noun

brittle, transparent substance made from melted and fused minerals such as silica.

hoarfrost

Noun

ice crystals that form as water vapor near objects becomes solid. Also called radiation frost.

ice

Noun

water in its solid form.

Encyclopedic Entry: ice

ice crystal

Noun

solid ice arranged in precise molecular form.

ice-minus bacteria

Noun

organism that makes it difficult for frost to form.

map

Noun

symbolic representation of selected characteristics of a place, usually drawn on a flat surface.

Encyclopedic Entry: map

moisture

Noun

wetness.

molecule

Noun

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

mountain

Noun

landmass that forms as tectonic plates interact with each other.

pane

Noun

sheet of glass or other material placed in a frame for a window.

pine

Noun

type of evergreen tree with needle-shaped leaves.

potato

Noun

plant native to the Americas.

predict

Verb

to know the outcome of a situation in advance.

radiation frost

Noun

ice crystals that form as water vapor near objects becomes solid. Also called hoarfrost.

refrigerator

Noun

space with artificially lowered temperature.

reliable

Adjective

dependable or consistent.

rhyme

Noun

word that has the same ending sound as another word.

rime

Noun

ice crystals that form in wet, windy conditions.

sailor

Noun

person who works aboard a ship.

Samuel Taylor Coleridge

Noun

(1772-1834) English poet.

saturate

Verb

to fill one substance with as much of another substance as it can take.

selective inverted sink (SIS)

Noun

method of preventing or reducing frost damage to crops by fanning cold, moist air up a chimney.

soy

Noun

beans, or fruit, of the soybean plant, native to Asia.

spruce

Noun

coniferous, or cone-bearing, tree.

temperature

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

Encyclopedic Entry: temperature

tomato

Noun

plant and fruit native to the Americas. Also considered a vegetable.

vapor

Noun

visible liquid suspended in the air, such as fog.

weather

Noun

state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

Encyclopedic Entry: weather

wind

Noun

movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

window frost

Noun

ice crystals that form when a window is exposed to freezing temperatures on one side and moist air on the other.

zucchini

Noun

type of vegetable (squash). Also called a courgette.

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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