National Geographic
National Geographic

Encyclopedic Entries

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A caldera is a depression created after a volcano partially collapses after releasing the majority of its magma chamber in an explosive eruption....

pyroclastic flow

Pyroclastic flows are volcanic phenomena that involve high-density mixtures of hot, fragmented solids and expanding gases.


Magma is a mixture of molten and semi-molten rock found beneath the surface of the Earth.

volcanic ash

Volcanic ash is made of tiny fragments of jagged rock, minerals, and volcanic glass. Ash is a product of explosive volcanic eruptions.

volcanic cone

A volcanic cone is the triangle-shaped hill formed as material from volcanic eruptions piles up around the volcanic vent, or opening in the Earth&rsqu...


A volcano is a feature in Earth's crust where molten rock is squeezed out onto the Earth's surface. Along with molten rock, volcanoes also release gas...

ocean gyre

A gyre is a circular ocean current formed by the Earth's wind patterns and the forces created by the rotation of the planet

Great Pacific Garbage Patch

The Great Pacific Garbage Patch is a collection of marine debris in the North Pacific Ocean. Marine debris is litter that ends up in oceans, seas, and...


Meteoroids are lumps of rock or iron that orbit the sun.


Meteorites are space rocks that fall to Earth's surface.


A meteor is a streak of light in the sky caused by a meteoroid passing through Earth's atmosphere.


A thermometer is an instrument that measures temperature.


An altimeter is a device that measures altitude, the distance of a point above sea level.


A barometer is a tool used to measure atmospheric pressure, also called barometric pressure


Nanotechnology is the study and manipulation of individual atoms and molecules.


A landslide is the movement of rock, earth, or debris down a sloped section of land.


Deltas form as rivers empty their water and sediment into another body of water, such as an ocean, lake, or another river.


A rainbow is a multicolored arc made by light striking water droplets.


A compass is a device that indicates direction. It is one of the most important instruments for navigation.


An isthmus is a narrow strip of land that connects two larger landmasses and separates two bodies of water


The horizon is the line that separates the Earth from the sky.


A gap is a low area between two high mountain peaks.


A divide is the elevated boundary between areas that are drained by different river systems.


A cove is a small, sheltered recess in the shoreline of a sea, lake, or river


Drought is an extended period of unusually dry weather when there is not enough rain.