Volcanoes: Facts about geology's fieriest features

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The reality ’s largest vent : Mauna Loa , which rises 30,000 feet ( 9,000 metre ) above the seafloor

turn of active volcanoes in the U.S.:165

Volcano erupting

Lava erupts from the Fagradalsfjall volcano in Grindavik, Iceland.

deadly volcanic eruption : The 1815 bang of Mount Tambora in Indonesia , which toss off up to 100,000 people

From lava fountains to towering ash clouds , vent grow some of the most spectacular geological result on the planet . volcano are cracks in Earth ’s insolence that allow liquefied rock and raging gas to escape . According to theU.S. Geological Survey(USGS ) , there are about 1,350 volcanoes worldwide that have the potentiality to push through . That does n’t count undersea vent , which would addanother several thousandto the list .

volcano are look at active if they have combust sometime in the past 11,700 years , a prison term period of time called the Holocene epoch . If they have n’t come out during the Holocene , they are view out . Sometimes people refer to volcano that have n’t erupted in a long time as " inactive , " but there ’s no scientific definition of that Son . It could mean a volcano that erupts on a regular basis but is currently unruffled , or it could relate to a vent that belike wo n’t ever erupt again .

A map showing the Pacific Ring of Fire

More than half of the world’s active volcanoes are in the Ring of Fire, which runs in a horseshoe shape from the southern tip of South America, up to Alaska and down through Japan and through the Pacific to New Zealand.

5 fast facts about volcanoes

Everything you need to know about volcanoes

How do volcanoes form?

Earth ’s top level , the crust , is made of cool , enured rock . But in some plaza , geologic processes make parts of the freshness to melt . Or the crust can crack open enough to let melted careen from the next level of Earth , the mantle , stand up to the surface .

One spot this take place is at the bounds of architectonic plate , which are the huge pieces of impertinence that fit together like teaser pieces and cover the surface of the satellite . At billet where two architectonic plates are pulling away from each other , magma — raging , liquefied rock — can rise from the mantle to the aerofoil , forming vent .

Volcanoes can also form where plate crash into each other . When one tectonic home plate pushes beneath another , it ’s calledsubduction . The home plate diving into Earth pull out down rocks and minerals full of water . When that water supply - rich rock gets put under pressure by the weight of the insolence pressing down on top of it , it can melt . This melting forms volcanoes .

A map of the world’s midocean ridges showing seam-like structures running through the Atlantic Ocean, the eastern Pacific and the Indian Ocean.

Midocean ridges, seen in red, are formed where two tectonic plates pull apart. They run through every ocean in a global network. Magma can ooze up at midocean ridges.

vent can also form at hotspots , which are places where a really hot plume of rock in the drape bubbles up , weakening the encrustation .

Where are volcanoes found?

The volcanoes that form where architectonic plate are pluck apart are now seen at midocean ridge , which are places under the ocean where two firearm of crust move by from each other . Two major midocean ridges are the Mid - Atlantic Ridge , which run down the center of the Atlantic Ocean like a zipper , and the East Pacific Rise , which runs along the west coast of North America and then out to ocean in the southern Pacific . The volcanoes that form where architectonic plates are pushing together happen anywhere that sea crust extend under sea encrustation , or anywhere that ocean crust run under the cheekiness that throw up the Continent . The main post to observe these types of volcano is the " Ring of Fire " that circulate the Pacific Ocean . There are more than 450 vent in the Ring of Fire , according to theNational Oceanic and Atmospheric Administration .

Volcanic hotspots , on the other bridge player , occur in the heart of continents . blistering mantle plume sit in one place for long catamenia of time while the freshness slowly creeps over them . Yellowstone National Park , the Hawaiian Islands , and American Samoa are all landscapes formed by hotspot volcanoes . hotspot are also base in Iceland , in the Afar neighborhood of Africa , and under the sea worldwide .

What types of volcanoes are there?

Cinder conesare round-eyed vent that take shape where vents , or openings , spit out ash tree and lava . They can be cone- or ellipse - shaped , usually with a arena - like volcanic crater at their summits .

When a cinder cone erupts over and over , it can evolve into astratovolcano . Stratovolcanoes are retinal cone - regulate volcanoes that ramp up up from layer after layer of lava and ash , one bam at a clip . They ’re also calledcomposite volcano . Mount Rainier in Washington is a famous stratovolcano .

carapace volcanoesare large , tolerant volcanoes made up of seeping lava course that erupt from multiple vent . Hawaii ’s Mauna Loa and Kilauea are both shell volcano . Though they do n’t form a classic cone shape , shield volcanoes can be massive : Mauna Loa has an estimated volume of 18,000 three-dimensional miles ( 75,000 cubic kilometers ) . The big shield volcano is Tamu Massif , and it sits on a seamount east of Japan , its summit 6,500 feet ( 1,980 m ) below the ocean aerofoil .

Glowing red lava splashes against dark, black rocks in a nighttime scene

(Image credit: USGS)

One terminal type of volcanic system is theLarge Igneous Province , a massive outpouring of lava made from rocks call basalt . These eruptions can flood jillion of square miles with lava that ’s over a mile thick . Luckily , there are no large igneous province active today . But scientist think that in the past , these huge eruptions make some of the major planet ’s biggest mass extinctions .

How do volcanoes erupt?

The first hint that a vent might recrudesce is usually a lot of tiny earthquakes . Some of these might be big enough that humankind can feel them ; others can be observe only by raw instruments . Either style , the temblor suggest that magma is act beneath the surface , pushing through breaks in the careen and causing the ground to tremble .

The ground may swell as unobserved magma flows toward the airfoil . Often , the volcano starts belching out more volcanic gas . Sometimes , new vent exposed in the ground so this gas can escape . The ground may even get hot as magma warms it from below . On some snow - overcompensate volcanoes , scientists watch for newfangled lakes forming near volcanic vents . These snowmelt lakes can reveal hotspots of magma below .

In a non - volatile outbreak , like those that materialise at Hawaii ’s volcanoes , lava fountains or oozes from cracks in the ground . The lava in these eccentric of volcano does n’t carry much dissolve gas , so it does n’t break through with a hatful of force . It ’s more like gooey syrup than a shaken - up soft drunkenness .

A snow-covered mountain is flanked by a large blue lake to the left and additional snowy mountainous terrain in the foreground.

(Image credit: USGS)

Explosive eruption , though , can blast vast amount of rock and ash tree thousands of feet into the air . The May 1980 outbreak of Mount St. Helens direct ash 12 miles ( 19 kilometre ) into the sky in the first 10 minutes of the explosion . Volcanoes like Mount St. Helens also often release pyroclastic period , which are avalanche of hot rock , gasolene and ash that spill down the slopes at more than 200 mph ( 320 klick / h ) . Pyroclastic rate of flow can be as red-hot as 1,300 F ( 700 C ) .

Explosive clap might also eject liquified lava flow rate and lava bombs , which are chunk of partially mellow out rock and roll that can take flight for mile . Some gelid volcano produce immense mudslides scream lahars when hot rock and hot gas disappear ice and nose candy on their slopes .

Volcano pictures

Lava outflow from Halema’uma‘‘u at the meridian of Kilauea the evening of Feb. 11 , 2025 . Some fountains arrive at 200 animal foot ( 60 meters ) gamey .

Mount St. Helens in June 2024 . Spirit Lake , to the left of the mountain , became a natural science laboratory for scientist to study the recovery of an ecosystem after an eruption . Although it was full of ash tree and had no O at first , flyspeck creature called phytoplankton started know in the lake again the same year , reinstate the nutrient web .

USGS geologist Don Swanson and his colleague Jim Moore examine a railcar forget in ash by the May 18 , 1980 , eruption of Mount St. Helens in Washington .

Two people with their backs to the camera kneel by a car buried up to its windows in rock. There is no vegetation. A helicopter sits in the background.

(Image credit: USGS)

Yellowstone National Park sits on a volcanic hotspot that erupted dramatically 640,000 days ago . There ’s no sign that the supervolcano will recrudesce so catastrophically in the near time to come , but the ballpark ’s geothermic features are a reminder of the heat beneath . Abyss Pool contains 181F ( 83 snow ) water that occasionally erupt without admonish , spewing steam and hot water 100 foundation ( 30 megabyte ) into the atmosphere .