• gorge
    The Yangtze River flows through the Three Gorges area.

    Lewis and Clark,
    Rock and Roll

    The Columbia River Gorge greatly challenged Lewis and Clark during their expedition of the Louisiana Purchase and the Pacific Northwest in 1805. Meriwether Lewis, William Clark and their Corps of Discovery were not only challenged by the landforms of the gorge, but also by the extreme weather that often halted their journey. The steep rocks near Celilo Falls and the rolling Columbia River near Cascade Rapids were particularly difficult. One could say that the success of the Lewis and Clark Expedition was based upon the "rock and roll" of the Columbia River Gorge!

    A gorge is a narrow valley with steep, rocky walls located between hills or mountains. The term comes from the French word gorge, which means throat or neck. A gorge is often smaller than a canyon, although both words are used to describe deep, narrow valleys with a stream or river running along their bottom.

    A number of natural forces form gorges. The most common is erosion due to streams or rivers. Streams carve through hard layers of rock, breaking down or eroding it. Sediment from the worn-away rock is then carried downstream. Over time, this erosion will form the steep walls of a gorge. The flooding of streams or rivers increases the speed and intensity of this erosion, creating deeper and wider gorges. The deep Talari Gorges in Mali, for instance, were formed by the Sngal River that flows into the Atlantic Ocean on the western coast of Africa.

    Geologic uplift also forms gorges. Geologic uplift is the upward movement of the Earths surface. Geologic uplift is often associated with earthquakes and orogeny, the process of creating mountains. During geologic uplift, rock layers beneath the Earths surface bump against the surface layers. Softer layers of surface rock erode.

    Erosion and geologic uplift often work together to create gorges. Parts of streams or rivers can be elevated, along with land, during the process of geologic uplift. As rivers or streams flow across this uplifted surface, waterfalls form. Over time, the power of the waterfall erodes the softer rock layers underneath, causing the original river bed to collapse and create a gorge. Macocha Gorge in the Jihomoravsk region of the Czech Republic was probably formed by the collapse of an underground cave that had been eroded by the Punkva River.

    The movement and melting of glaciers can also produce gorges. Glaciers cut deep valleys into the Earths surface. These rivers of ice can create huge canyons and sharp, steep gorges. As glaciers melt, or retreat, these gorges and canyons are exposed. The Columbia River Gorge, located in the U.S. states of Washington and Oregon, was partially created by glacial retreat during the last Ice Age.

    Engineers have purposely flooded gorges in order to create waterways and dams. These dams generate hydroelectricity, or electricity powered by water. The Three Gorges Dam on the Yangtze River in China is probably the most famous example of such a project. Upstream from the dam, the Qutang, Wu, and Xilang gorges were partially submerged in order to create a waterway. The new waterway would allow freight ships to navigate from the East China Sea, part of the Pacific Ocean, to the city of Chongqing, about 2,250 kilometers (1,400 miles) inland. The 26 turbines of the Three Gorges Dam generate approximately 18,000 megawatts of electricity for Shanghai and other cities. However, many people worry about the environmental impacts of the dam and criticize the fact that more than a million Chinese families were forced to move from their homes near the gorges in order to complete the construction.

    Many geological discoveries have been made at gorges because gorges often expose layers of rock that go back thousands of years. Olduvai Gorge in Tanzania has layers dating as far back as 2 million years. The Olduvai Gorge is famous for the fossils and ancient tools found there by scientists Louis, Mary, and Richard Leakey. These remains of ancient animals and plants provide clues about early humans.

  • Term Part of Speech Definition Encyclopedic Entry
    approximately Adjective

    generally or near an exact figure.

    associate Verb

    to connect.

    canyon Noun

    deep, narrow valley with steep sides.

    Encyclopedic Entry: canyon
    cave Noun

    underground chamber that opens to the surface. Cave entrances can be on land or in water.

    collapse Verb

    to fall apart completely.

    Corps of Discovery Noun

    (1804-1806) group of explorers, led by Meriwether Lewis and William Clark, who led a journey from the eastern U.S. to the Pacific Coast and back. Also a name for the journey itself.

    dam Noun

    structure built across a river or other waterway to control the flow of water.

    downstream Noun

    in the direction of a flow, toward its end.

    earthquake Noun

    the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

    elevate Verb

    to raise higher than the surrounding area.

    engineer Noun

    person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).

    erode Verb

    to wear away.

    erosion Noun

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

    Encyclopedic Entry: erosion
    flood Verb

    to overflow or cover in water or another liquid.

    fossil Noun

    remnant, impression, or trace of an ancient organism.

    Encyclopedic Entry: fossil
    freight Noun

    goods transported by air, land, or sea for profit.

    generate Verb

    to create or begin.

    geologic uplift Noun

    upward movement of rock layers beneath the Earth's surface.

    glacial retreat Noun

    process by which glaciers melt faster than precipitation can replace the ice.

    glacier Noun

    mass of ice that moves slowly over land.

    Encyclopedic Entry: glacier
    gorge Noun

    deep, narrow valley with steep sides, usually smaller than a canyon.

    Encyclopedic Entry: gorge
    hill Noun

    land that rises above its surroundings and has a rounded summit, usually less than 300 meters (1,000 feet).

    Encyclopedic Entry: hill
    hydroelectricity Noun

    power generated by moving water converted to electricity. Also called hydroelectric energy or hydroelectric power.

    Ice Age Noun

    last glacial period, which peaked about 20,000 years ago.

    landform Noun

    specific natural feature on the Earth's surface.

    Encyclopedic Entry: landform
    Lewis and Clark Expedition Noun

    (1804-1806) first journey by U.S. explorers to the Pacific Coast and back to U.S. territory.

    Louisiana Purchase Noun

    (1803) land bought by the United States from France, extending from the Mississippi River to the Rocky Mountains, and Canada to the Gulf of Mexico.

    mountain Noun

    landmass that forms as tectonic plates interact with each other.

    navigate Verb

    to plan and direct the course of a journey.

    Olduvai Gorge Noun

    large valley in Tanzania, known for its abundance of archaeological sites.

    orogeny Noun

    the way mountains are formed.

    purposely Adverb

    intentionally or done with a specific purpose.

    rapids Noun

    areas of fast-flowing water in a river or stream that is making a slight descent.

    Encyclopedic Entry: rapids
    river bed Noun

    material at the bottom of a river.

    rock Noun

    natural substance composed of solid mineral matter.

    sediment Noun

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

    Encyclopedic Entry: sediment
    stream Noun

    body of flowing water.

    Encyclopedic Entry: stream
    submerge Verb

    to put underwater.

    Three Gorges Dam Noun

    electrical power plant along the Yangtze River in China.

    tool Noun

    instrument used to help in the performance of a task.

    turbine Noun

    machine that captures the energy of a moving fluid, such as air or water.

    upstream Adjective

    toward an elevated part of a flow of fluid, or place where the fluid passed earlier.

    valley Noun

    depression in the Earth between hills.

    waterfall Noun

    flow of water descending steeply over a cliff. Also called a cascade.

    Encyclopedic Entry: waterfall
    waterway Noun

    body of water that serves as a route for transportation.

    weather Noun

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

    Encyclopedic Entry: weather