Craters produced by the collision of a meteorite with the Earth (or another planet or moon) are called impact craters. The high-speed impact of a large meteorite compresses, or forces downward, a wide area of rock. The pressure pulverizes the rock. Almost immediately after the strike, however, the pulverized rock rebounds. Enormous amounts of shattered material jet upward, while a wide, circular crater forms where the rock once lay. Most of the material falls around the rim of the newly formed crater.
The Earth’s moon has many craters. Most were formed when meteors, bodies of solid matter from space, slammed into the lunar surface millions of years ago. Because the moon has almost no atmosphere, there is hardly any wind, erosion, or weathering. Craters and debris, called ejecta, from millions of years ago are still crystal-clear on the moon’s surface. Many of these craters are landmarks. Craters on the moon are named after everyone from American astronaut Buzz Aldrin to ancient Greek philosopher Zeno.
Many impact craters are found on the Earth’s surface, although they can be harder to detect. One of the best-known craters on Earth is Meteor Crater, near Winslow, Arizona. The crater was created instantly when a 50-meter (164-foot), 150,000-ton meteorite slammed into the desert about 50,000 years ago. Meteor Crater is 1.2 kilometers (0.75 miles) in diameter and 175 meters (575 feet) deep.
The Chicxulub Crater, on Mexico’s Yucatan Peninsula, was most likely created by a comet or asteroid that hit Earth about 65 million years ago. The crater is 180 kilometers (112 miles) wide and 900 meters (3,000 feet) deep. The object that created the Chicxulub Crater was probably about 10 kilometers (6 miles) wide.
The impact was so powerful the crater is called the Chicxulub Extinction Event Crater. Scientists say half the species on Earth—including the dinosaurs—went extinct as a result of the impact. The event was more than a billion times more explosive than all the atomic bombs ever detonated on Earth.
Impact craters are found on most of the solar system’s rocky planets and moons. The so-called “gas giants” of the solar system—Jupiter, Saturn, Uranus, and Neptune—don’t have craters. These planets are made up almost entirely of gases, so there is no hard surface for a meteor to impact. Meteors entering the atmosphere of a gas giant simply break up.
Cratering is a rare occurrence in the solar system today. Planets, moons, comets, and other celestial bodies have fairly stable orbits that do not interact with each other. Meteors do collide with planets—including Earth—every day. However, most of these meteors are the size of a speck of dust and do not cause any cratering. Most meteors burn up in the atmosphere as “shooting stars” before ever colliding with the surface of the Earth.
Volcanic activity often creates craters. Some volcanic craters are deep and have steep sides. Others are wide and shallow.
A crater is not the same thing as a caldera. Craters are formed by the outward explosion of rocks and other materials from a volcano. Calderas are formed by the inward collapse of a volcano’s magma chamber. Craters are usually much smaller features than calderas, and calderas are sometimes considered giant craters.
Craters at the top of volcanoes are called summit craters. Summit craters are where volcanic material is at or near the Earth’s surface. Volcanoes may have one summit crater, such as Mount Fuji in Japan. Or they may have several. Mount Etna, in Italy, has four.
Some volcanoes are calm enough that scientists can get close to the lava in the summit crater. Mount Erebus, a volcano in Antarctica, has a lava lake in its summit crater. Lava lakes are where magma has bubbled up to the surface. Volcanologists can fly over Mount Erebus’ summit crater to see how the lava lake is behaving and predict future behavior.
Volcanic material in some summit craters is near the surface, but not visible. Although Mount Fuji is an active volcano and magma and gases sit below the summit crater, the risk of an eruption is very low. Mount Fuji, Japan’s highest mountain, is one of the most popular places in the country to hike.
Craters that form on the sides of volcanoes are called flank craters. Eruptions from flank craters can be much more dangerous than eruptions from summit craters. Flank craters can form at lower altitudes than summit craters, near hillside towns. Lava, gas, rocks, and other material ejected from a flank crater can rush down the side of a mountain in a phenomenon called a pyroclastic flow. Mount Etna, one of the most active volcanoes in Europe, has had a number of dangerous eruptions. In 1928, the eruption of a flank crater completely destroyed the village of Mascali.
Over a long period of time, small and non-explosive eruptions may fill a volcanic crater with new material. At Mount St. Helens, in the U.S. state of Washington, for example, a large crater formed when a major eruption in 1980 tore off 400 meters (1,300 feet) of the mountaintop. Soon after, smaller eruptions began piling up lava and volcanic ash on the crater floor, slowly rebuilding the mountain.
Volcanoes can also create craters when the magma comes into contact with water. Magma flowing or bubbling beneath a volcano can sometimes interact with groundwater in the area. When this happens, a small explosion occurs and a crater forms around the explosion. This type of volcanic crater is called a maar.
Often, a maar will fill with water and become a shallow crater lake. The thin floors of these lakes are actually the roofs of volcanic vents, waiting to come into explosive contact with water once again. The Seward Peninsula, in the U.S. state of Alaska, is filled with maars that form as magma encounters not groundwater, but permafrost.
A third type of crater is formed by an explosion. When materials or chemicals explode, the explosion displaces all the material around it. The debris often lands in a circular pattern around the site of the explosion, creating a crater.
Explosions can be natural or artificial. The explosion that creates a maar, for example, occurs naturally when water interacts with superhot magma from a volcano. Maars are a type of explosion crater as well as a volcanic crater.
Artificial explosions that form craters usually happen underground. The explosion pulverizes or vaporizes material underground, and the earth above sinks. Craters formed by underground explosions are called subsidence craters. (Craters formed by explosions at or near the surface of the Earth are simply called explosion craters.)
Drilling underground for oil and natural gas can lead to explosions and subsidence craters. Machinery can sometimes encounter a pocket of natural gas that is under extremely high pressure. When drilling machinery punctures the pocket of natural gas, the overlying rock layers may not be able to contain it. Like an enormous balloon, the gas pocket pops. As the gas is released in the explosion, a crater forms in the empty space.
A specific type of subsidence crater is formed by an underground nuclear explosion. Most nuclear testing is conducted in underground facilities. As the explosion displaces massive amounts of material, the earth above it sinks. In fact, subsidence craters caused by underground nuclear explosions are sometimes called sinks. The Nevada Test Site, in the remote deserts of the U.S. state of Nevada, is pockmarked with nuclear subsidence craters.
The debris in and around nuclear subsidence craters often comes into contact with radioactive material. For this reason, access to these sites is restricted.
Finding CratersAlthough impact craters are found all around the world, they can be very hard to detect. Before the widespread use of aerial and satellite imagery, many craters went undetected. One of the reasons Meteor Crater is so well-known is because the stark Arizona desert makes it an obvious feature of the area’s physical geography.The forces of wind, rivers, precipitation, for instance, can scrape away evidence of a crater. Some areas are also geologically complex, where a meteor’s impact may be more pronounced among some rocks and less by others. Some rocks are also more vulnerable to the forces of weathering and erosion. These forces can mask the traditional circular pattern of an impact crater.Spider Crater, Western Australia, for example, is an unusual feature that puzzled geologists until the 1970s. The winding series of chasms and ridges radiating from a central area resemble a giant arachnid, not a circular crater. Geologists were able to identify Spider as an impact crater only after looking at rocks unearthed from the feature’s central region. There, they discovered shatter cones, rare rocks that only form in the bedrock beneath impact craters.Landscape and vegetation can also hide impact craters. The largest impact crater in the United States, for instance, was unknown until the 1980s. The Chesapeake Bay impact crater was hidden beneath the muddy waters of the Chesapeake Bay and the Atlantic Ocean for about 35 million years. The submarine crater, discovered through oil drilling exploration, was, like Spider Crater, marked by rocks only found at impact craters.
Some craters on Mars hint that liquid water was probably present at some point in the planet's past. Rampart craters are a type of impact crater found only on Mars. Unlike craters on the moon, where debris, called ejecta, from the impact is spread out in neat lines, rampart craters show ejecta curving out in smooth, flowing lineslike a mudflow. Rampart craters look more like splashes than explosions.
Bacteria Will SurviveYou Wont
The impact of a meteorite that would result in the creation of a Chicxulub-sized crater is something astronomers call an extinction-level event (ELE) or biotic crisis. Meteorites are just one possible cause of an ELE. ELEs have happened more than a dozen times in Earths history.
Extinction-level events actually have little effect on Earths biodiversity. Most life on Earth is microbial. Microbes, such as bacteria and algae, are not significantly affected by ELEs. Its only the larger life formstrees, dinosaurs, peoplethat face biotic crises.MakhteshimA makhtesh is a type of circular depression only found in the Negev Desert of Israel. Although often called craters, makhteshim are not created by explosions or impacts. They are created by the process of erosion wearing away softer rocks underlying a harder upper layer. The upper layer ultimately collapses under its own weight, forming a bowl-shaped depression that resembles a crater.
Term Part of Speech Definition Encyclopedic Entry access Noun
ability to use.
active volcano Noun
volcano that has had a recorded eruption since the last glacial period, about 10,000 years ago.
existing, moving, growing, or operating in the air.
the distance above sea level.
Encyclopedic Entry: altitude ancient Adjective
irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.
person who takes part in space flights.
layers of gases surrounding a planet or other celestial body.
Encyclopedic Entry: atmosphere atomic bomb Noun
explosive device that draws energy from the interaction of atomic nuclei. Also called an atom bomb, a-bomb, or nuclear bomb.
solid rock beneath the Earth's soil and sand.
Encyclopedic Entry: bedrock Buzz Aldrin Noun
(Edwin Eugene Aldrin, Jr., born 1930) U.S. astronaut.
large depression resulting from the collapse of the center of a volcano.
Encyclopedic Entry: caldera chasm Noun
a deep opening in the earth's surface.
Chicxulub Crater Noun
impact crater on the Yucatan Peninsula, formed about 65 million years ago.
to crash into.
celestial object made up of ice, gas, and dust that orbits the sun and leaves a tail of debris.
to press together in a smaller space.
bowl-shaped depression formed by a volcanic eruption or impact of a meteorite.
Encyclopedic Entry: crater debris Noun
remains of something broken or destroyed; waste, or garbage.
indentation or dip in the landscape.
area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.
Encyclopedic Entry: desert detect Verb
to cause something to explode.
width of a circle.
very large, extinct reptile chiefly from the Mesozoic Era, 251 million to 65 million years ago.
tiny, dry particles of material solid enough for wind to carry.
Encyclopedic Entry: dust Earth Noun
our planet, the third from the Sun. The Earth is the only place in the known universe that supports life.
Encyclopedic Entry: Earth ejecta Noun
material ejected from a crater, usually by an erupting volcano or meteorite impact.
act in which earth is worn away, often by water, wind, or ice.
Encyclopedic Entry: erosion eruption Noun
release of material from an opening in the Earth's crust.
process of complete disappearance of a species from Earth.
flank crater Noun
depression formed by volcanic activity on the sides of a volcano.
state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.
gas giant Noun
one of the four enormous outermost planets in the solar system (Jupiter, Saturn, Neptune, Uranus), composed mostly of gases instead of rock. Also called a Jovian planet.
person who studies the physical formations of the Earth.
water found in an aquifer.
Encyclopedic Entry: groundwater impact crater Noun
circular surface depression made by the impact of a meteorite.
largest planet in the solar system, the fifth planet from the Sun.
a prominent feature that guides in navigation or marks a site.
the geographic features of a region.
Encyclopedic Entry: landscape lava Noun
molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.
having to do with Earth's moon or the moons of other planets.
depression formed as magma reacts with groundwater.
mechanical appliances or tools used in manufacturing.
molten, or partially melted, rock beneath the Earth's surface.
Encyclopedic Entry: magma magma chamber Noun
underground reservoir that holds molten rock.
rocky debris from space that enters Earth's atmosphere. Also called a shooting star or falling star.
Encyclopedic Entry: meteor Meteor Crater Noun
impact crater near Winslow, Arizona, formed about 50,000 years ago.
type of rock that has crashed into Earth from outside the atmosphere.
Encyclopedic Entry: meteorite Moon Noun
Earth's only natural satellite.
natural gas Noun
type of fossil fuel made up mostly of the gas methane.
Encyclopedic Entry: natural gas Neptune Noun
eighth planet from the sun in our solar system.
Nevada Test Site Noun
testing site for nuclear weapons and other military products in the southern Nevada desert. Nuclear weapons testing was discontinued there in 1992.
nuclear explosion Noun
large release of energy as a result of a reaction between atomic nuclei or nuclear particles.
fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.
oil drilling Noun
process of digging below the surface of the Earth for oil.
path of one object around a more massive object.
piece of land jutting into a body of water.
Encyclopedic Entry: peninsula permafrost Noun
permanently frozen layer of the Earth's surface.
Encyclopedic Entry: permafrost phenomenon Noun
an unusual act or occurrence.
person who studies knowledge and the way people use it.
physical geography Noun
study of the natural features and processes of the Earth.
large, spherical celestial body that regularly rotates around a star.
Encyclopedic Entry: planet pockmarked Adjective
scarred with many small indentations.
all forms in which water falls to Earth from the atmosphere.
Encyclopedic Entry: precipitation predict Verb
to know the outcome of a situation in advance.
to crush and make into dust or powder.
to penetrate or poke through.
pyroclastic flow Noun
current of volcanic ash, lava, and gas that flows from a volcano.
Encyclopedic Entry: pyroclastic flow radioactive Adjective
having unstable atomic nuclei and emitting subatomic particles and radiation.
unusual or uncommon.
distant or far away.
long, narrow elevation of earth.
large stream of flowing fresh water.
Encyclopedic Entry: river satellite imagery Noun
photographs of a planet taken by or from a satellite.
sixth planet from the sun.
shatter cone Noun conical structure produced in rock by intense mechanical shock, usually associated with a meteor impact. shooting star Noun
rocky debris from space that enters Earth's atmosphere. Also called a meteor.
solar system Noun
the sun and the planets, asteroids, comets, and other bodies that orbit around it.
group of similar organisms that can reproduce with each other.
severe, striking, or clear-cut.
subsidence crater Noun
depression formed as the result of an underground explosion.
highest point of a mountain.
large, gaseous planet in the solar system, seventh from the sun.
to turn into gas, or vapor.
all the plant life of a specific place.
small human settlement usually found in a rural setting.
Encyclopedic Entry: village visible Adjective
able to be seen.
having to do with volcanoes.
volcanic ash Noun
fragments of lava less than 2 millimeters across.
Encyclopedic Entry: volcanic ash volcanic vent Noun
opening in the Earth's crust where lava and gases escape to the Earth's surface or atmosphere.
an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.
Encyclopedic Entry: volcano volcanologist Noun
scientist who studies volcanoes.
the breaking down or dissolving of the Earth's surface rocks and minerals.
Encyclopedic Entry: weathering 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.
(340-265 BCE) Greek philosopher.