• rift valley
    Parts of the East African Rift are nicknamed the "Cradle of Mankind."

    Photograph by Emory Kristof

    Let Her Rift
    With so much volcanic and tectonic activity going on there, the East African Rift Valley is a potent power source. The United Nations Environment Program is developing a geothermal energy program that would tap into its potential. The program would convert the heat created by the rift valley's underground activity into electricity through a series of steam wells. One of the wells in Kenya produces enough power for 5,700 homes! If successful, this program would provide a sustainable energy source for millions of people, many of whom do not have access to electricity today.

    Rift Valley Fever
    Rift Valley Fever (RVF) is a disease that affects livestock such as sheep and cattle. The disease was first diagnosed in eastern Africa and is rarely documented outside that area. Rift Valley Fever can be fatal to livestock, causing economic damage to the agricultural communities in Kenya, Tanzania, and Somalia. People are rarely infected with RVF, but when they are, it can sometimes lead to blindness and death.

    Finds in the Rift
    Many important anthropological discoveries have been made in the East African Rift Valley. Lucy, a famous 3.2 million-year-old Australopithicus afarensis, was found in Ethiopia's Afar Depression. Turkana Boy, a 1.5 mill-year-old Homo erectus, was discovered in the Gregory Rift. Fossils like Lucy and Turkana Boy help scientists understand human evolution.

    Superior Rift
    Not all rift valleys are active. Lake Superior sits atop an ancient rift valley, the Keweenawan Rift, created during the Precambrian Era about 1.1 billion years ago. The continent of North America was rifting, but never entirely split. Lake Superior sits at the northern end of the -shaped Keweenawan Rift, which stretches about 2,000 kilometers (1,200 miles).

    A rift valley forms where the Earth’s crust, or outermost layer, is spreading or splitting apart. This kind of valley is often narrow, with steep sides and a flat floor.

    Rift valleys are also called grabens, which means “ditch” in German. While there is no official distinction between a graben and a rift valley, a graben usually describes a small rift valley.

    Rift valleys differ from river valleys and glacial valleys because they are created by tectonic activity and not by the process of erosion.

    Rift valleys are created by plate tectonics. Tectonic plates are the huge rocky slabs made up of the Earth's crust and upper mantle. They are constantly in motion—shifting against each other, falling beneath one another (a process called subduction), crashing against one another. Tectonic plates also tear apart from each other. Where plates move apart, the Earth’s crust separates, or rifts. Rift valleys can lead to the creation of entirely new continents, or deepen valleys in existing ones.

    Many rift valleys have been found underwater, along the large ridges that run throughout the ocean. These mid-ocean ridges are formed as tectonic plates move away from one another. As the plates separate, molten rock from the Earth’s interior may well up and harden as it contacts the sea, forming new oceanic crust at the bottom of the rift valley.

    This occurs along the northern crest of the Mid-Atlantic Ridge, where the North American plate and the Eurasian plate are splitting apart. The Mid-Atlantic Ridge rifts at an average of 2.5 centimeters (1 inch) per year. Over millions of years, the Mid-Atlantic Ridge has formed rift valleys as wide as 15 kilometers (9 miles).

    In the Pacific Ocean, the East Pacific Rise has created rift valleys where the Pacific plate is separating from the North American plate, Riviera plate, Cocos plate, Nazca plate, and Antarctic plate. (The Pacific plate is the largest on Earth.) Like many underwater rift valleys, the East Pacific Rise is dotted with hydrothermal vents. The geologic activity beneath the underwater rift valley creates these vents, which spew super-heated water and sometimes-toxic vent fluids into the ocean.

    There are only two rift valleys on Earth within continental crust, the Baikal Rift Valley and the East African Rift. Tectonic activity splits continental crust much in the same way it does along mid-ocean ridges. As the sides of a rift valley move farther apart, the floor sinks lower.

    The deepest continental rift valley on Earth is the Baikal Rift Valley in the Siberian region of northeastern Russia. Lake Baikal, the deepest and oldest freshwater lake in the world, lies in the Baikal Rift Valley. Here, the Amur plate is slowly tearing itself away from the Eurasian plate, and has been doing so for about 25 million years. The deepest part of Lake Baikal is 1,187 meters (3,893 feet), and getting deeper every year. Beneath this is a layer of soft sediment reaching several kilometers. The actual bottom of the rift extends about 10 kilometers (6.2 miles) deep.

    Great Rift Valley

    Historically, geologists and geographers referred to the "Great Rift Valley System" which stretched from the Middle East in the north to Madagascar in the south. The area is geologically active, and features hot springs, geysers, and frequent earthquakes. Today, however, the Great Rift Valley only remains as a cultural concept. Each of the rift valleys in the area are connected, but not part of a single system.

    The Jordan Rift Valley stretches between Jordan and Israel in western Asia. The Jordan Rift Valley includes the Dead Sea, at 377 meters (1,237 feet) the lowest land elevation on Earth. Unlike Lake Baikal, however, the Dead Sea was not formed entirely by the rift beneath it. The so-called Dead Sea Transform is a very geologically complex area, where many tectonic plates interact in many ways.

    South of the Jordan Rift Valley is the Red Sea Rift. Millions of years ago, the Arabian Peninsula was connected to Africa. The Arabian and African plates rifted apart and the Indian Ocean flooded the rift valley, creating the Red Sea. The rift continues, and the Red Sea, rich in marine life, widens every year.

    South of the Red Sea Rift lies the massive, complex East African Rift. This system of rift valleys is usually what people think of as the "Great Rift Valley." Throughout the East African Rift, the African plate is splitting in two. The Nubian plate carries most of the continent, while the smaller Somali plate carries Horn of Africa. As the rift continues, the rift valley may sink enough that the Gulf of Aden will flood it. The Horn of Africa (sitting on the Somali plate) would become a continental island, like Madagascar or New Zealand.

    The East African Rift includes many smaller rift valleys and other areas of tectonic activity. The Afar Triple Junction sits at the meeting of three tectonic plates on the Horn of Africa. At the Afar Triple Junction, the Arabian plate, Nubian plate and Somali plate are all tearing away from each other.

    The two main divisions are the Gregory Rift and the Western Rift. The Gregory Rift stretches from the Red Sea and Gulf of Aden (the Afar Triple Junction) as far south as Mount Kilimanjaro, Tanzania. The Western Rift, also called the Albertine Rift, includes many of the African Great Lakes, from Lake Malawi through Lake Tanganyika, Lake Kivu, Lake Edward, and Lake Albert.

  • Term Part of Speech Definition Encyclopedic Entry
    African Great Lakes Noun

    system of lakes in and around the Great Rift Valley: Lake Albert, Lake Edward, Lake Kivu, Lake Malawi, Lake Tanganyika, Lake Turkana, and Lake Victoria. Also called the Rift Valley Lakes and the East African Lakes.

    anthropology Noun

    science of the origin, development, and culture of human beings.

    Encyclopedic Entry: anthropology
    concept Noun

    idea.

    continent Noun

    one of the seven main land masses on Earth.

    Encyclopedic Entry: continent
    continental crust Noun

    thick layer of Earth that sits beneath continents.

    continental island Noun

    land once connected to a continent but broken off by shifting tectonic plates.

    crest Noun

    the top of a wave.

    crust Noun

    rocky outermost layer of Earth or other planet.

    Encyclopedic Entry: crust
    Dead Sea Noun

    body of water on the border between Israel and Jordan; the lowest point within land (400 meters, or 1,312 feet, below sea level).

    earthquake Noun

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

    East Pacific Rise Noun

    mid-ocean ridge where several tectonic plates are moving apart from one another.

    elevation Noun

    height above or below sea level.

    Encyclopedic Entry: elevation
    erosion Noun

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

    Encyclopedic Entry: erosion
    freshwater Noun

    water that is not salty.

    geographer Noun

    person who studies places and the relationships between people and their environments.

    geologist Noun

    person who studies the physical formations of the Earth.

    geyser Noun

    natural hot spring that sometimes erupts with water or steam.

    Encyclopedic Entry: geyser
    glacial valley Noun

    depression in the earth created by a moving glacier.

    graben Noun

    small rift valley.

    Great Rift Valley system Noun

    series of faults and other sites of tectonic activity stretching from southwestern Asia to the Horn of Africa.

    Horn of Africa Noun

    large peninsula in northeast Africa, including the countries of Somalia, Djibouti, Eritrea, and Ethiopia. Also called the Somali Peninsula.

    hot spring Noun

    small flow of water flowing naturally from an underground water source heated by hot or molten rock.

    hydrothermal Adjective

    related to hot water, especially water heated by the Earth's internal temperature.

    mantle Noun

    middle layer of the Earth, made of mostly solid rock.

    Encyclopedic Entry: mantle
    Mid-Atlantic Ridge Noun

    underwater mountain range that runs from Iceland to Antarctica.

    mid-ocean ridge Noun

    underwater mountain range.

    molten Adjective

    solid material turned to liquid by heat.

    oceanic crust Noun

    thin layer of the Earth that sits beneath ocean basins.

    plate tectonics Noun

    movement and interaction of the Earth's plates.

    rift Noun

    break in the Earth's crust created by it spreading or splitting apart.

    rift valley Noun

    depression in the ground caused by the Earth's crust spreading apart.

    Encyclopedic Entry: rift valley
    river valley Noun

    depression in the earth caused by a river eroding the surrounding soil.

    sediment Noun

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

    Encyclopedic Entry: sediment
    Siberia Noun

    region of land stretching across Russia from the Ural Mountains to the Pacific Ocean.

    subduction Noun

    process of one tectonic plate melting or going beneath another.

    tectonic activity Noun

    movement of tectonic plates resulting in geologic activity such as volcanic eruptions and earthquakes.

    tectonic plate Noun

    large, moveable segment of the Earth's crust.

    toxic Adjective

    poisonous.

    valley Noun

    depression in the Earth between hills.

    vent Noun

    crack in the Earth's crust that spews hot gases and mineral-rich water.

    vent fluid Noun

    chemicals ejected by hydrothermal vents.

    well up Verb

    to swell or build up.

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