If you've ever been to the beach, you've been on a coast. The coast is the land along a sea. The boundary of a coast, where land meets water, is called the coastline.

Waves, tides, and currents help create coastlines. When waves crash onto shore, they wear away at, or erode, the land. But they also leave behind little parts of the sea, such as shells, sand dollars, seaweeds, and hermit crabs. Sometimes these objects end up as more permanent parts of the coastline.

Coastal changes can take hundreds of years. The way coasts are formed depends a lot on what kind of material is in the land and water. The harder the material in the land, the harder it is to erode. Coastlines of granite, a hard rock, stay pretty stable for centuries. Sugarloaf Mountain, on the coast of Rio de Janeiro, Brazil, is made mostly of granite and quartz. It has been a landmark for centuries.

The famous White Cliffs of Dover, in England, are made of calcium carbonate. This is a soft material and erodes easily. However, it exists in such great quantities that years of erosion have not made a visible impact on the coastline. The White Cliffs are a landmark of the English coast of the English Channel. (The other coast is French.)

The sandy coastlines of islands, on the other hand, change almost daily. The island of Mont Saint Michel is only an island when the tide is in. It is part of the coast of France during low tide. Islands are also the site of Earth's newest coastlines, like a Tongan island created in March 2009 by the eruption of the volcano Hunga Tonga-Hunga Haapai. The "Big Island" of Hawaii, created by five volcanoes, sometimes expands its coastline when one of its active volcanoes, Mauna Loa or Kilauea, erupts. If lava flows reach the ocean, the lava cools and forms new coastline along the Pacific Ocean.

Tides, the rise and fall of the ocean, affect where sediment and other objects are deposited on the coast. The water slowly rises up over the shore and then slowly falls back again, leaving material behind. In places with a large tidal range (the area between high tide and low tide,) waves deposit material such as shells and hermit crabs farther inland. Areas with a low tidal range have smaller waves that leave material closer to shore.

Waves that are really big carry a lot of energy. The larger the wave, the more energy it has, and the more sediment, or particles of rock, it will move. Coastlines with big beaches have more room for waves to spread their energy and deposits. Coastlines with small, narrow beaches have less room for waves to spread out. All the waves' energy is focused in a small place. This gives the small beaches a tattered, weathered look. Sandy beaches are washed away, and rocky coastlines are sometimes cracked by strong waves.

Because coasts are dynamic, or constantly changing, they are important ecosystems. They provide unique homes for marine plants, animals, and insects. Coasts can be icy, like the Shackleton Coast of Antarctica, or desert, like the Skeleton Coast of Namibia.

Coasts help us understand natural events, such as weather and changing sea levels. During storms, coasts are the first places to be flooded. Some coasts have coastal plains. Coastal plains are pieces of flat, low-lying land that can become visible when sea levels start decreasing.

Coasts, as beautiful as they tend to be, have it rough sometimes. They are affected by pollution, oil spills, and garbage from both land and sea. Pollution negatively affects the way a coast looks and is damaging to the marine life that lives there.

People visit the coast on vacation to participate in activities like fishing, boating, and swimming.

In the United States, coasts can be a reference to culture as much as physical geography. For example, West Coast people in California identify with a different type of culture, or way of life, than East Coast residents in New York City or Washington, D.C. The southern Gulf Coast of New Orleans, Louisiana, has yet a different cultural association.

This cultural connection to the coast shows up in many different ways, including food and leisure activities. Residents of the Gulf Coast, for instance, are more familiar with food made from shrimp, a seafood native to the warm waters of the Gulf of Mexico. Maine, on the northern East Coast, is famous for its lobster.

coast
Rocky coasts can be dangerous.

The Most Coast
. . . Canada has 202,080 kilometers (125,567 miles) of coastline.

Short But Sweet
. . . Monaco has 4 kilometers (2.5 miles) of coastline.

Banks and Shores
Technically, the land next to rivers and lakes is coastal. But river coasts are called banks and lake coasts are called shores.

Noun

narrow strip of land that lies along a body of water.

calcium carbonate
Noun

chemical compound (CaCO3) found in most shells and many rocks.

Noun

edge of land along the sea or other large body of water.

Noun

low, flat land lying next to the ocean.

coastline
Noun

outer boundary of a shore.

culture
Noun

learned behavior of people, including their languages, belief systems, social structures, institutions, and material goods.

Noun

steady, predictable flow of fluid within a larger body of that fluid.

decrease
Verb

to lower.

dynamic
Adjective

always changing or in motion.

East Coast
Noun

Atlantic coast of the United States.

Noun

community and interactions of living and nonliving things in an area.

energy
Noun

capacity to do work.

English Channel
Noun

strip of the Atlantic Ocean between southeast England and northwest France.

erode
Verb

to wear away.

flood
Verb

to overflow or cover in water or another liquid.

garbage
Noun

trash or waste material.

granite
Noun

type of hard, igneous rock.

Gulf Coast
Noun

land in the United States surrounding the Gulf of Mexico.

hermit crab
Noun

type of marine animal (crustacean) that uses found materials, such as other creatures' shells, as its shell.

high tide
Noun

water level that has risen as a result of the moon's gravitational pull on the Earth.

Noun

body of land surrounded by water.

low tide
Noun

water level that has dropped as a result of the moon's gravitational pull on the Earth.

marine
Adjective

having to do with the ocean.

oil spill
Noun

accidental release of petroleum products into a body of water, either by an oil tanker or an offshore oil rig.

Noun

introduction of harmful materials into the environment.

quantity
Noun

amount.

quartz
Noun

common type of mineral.

sand dollar
Noun

type of marine animal (sea urchin) that is flat and lives on the ocean floor.

Noun

base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.

seaweed
Noun

marine algae. Seaweed can be composed of brown, green, or red algae, as well as "blue-green algae," which is actually bacteria.

Noun

solid material transported and deposited by water, ice, and wind.

shell
Noun

hard outer covering of an animal.

tidal range
Noun

the difference in height between an area's high tide and low tide.

Noun

rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

wave
Noun

moving swell on the surface of water.

weather
Verb

to change as a result of exposure to wind, rain, or other atmospheric conditions.

Noun

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

West Coast
Noun

Pacific coast of the United States, usually excluding Alaska.