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Volcanoes

Volcanoes

Volcanoes | Get a Volcano Kit | Make a Plan | Prepare | During the Eruption | After the Eruption


vol·ca·no

A mountain or hill, typically conical, having a crater or vent through which lava, rock fragments, hot vapor, and gas are or have been erupted from the earth's crust

Volcanoes have forever fascinated humans. This marvelous and unbelievable explosion of the Earth's crust has also been one of the most feared natural disasters throughout history. The fear of volcanoes has been fueled throughout history with the help of legendary volcanic eruptions such as the eruption of Mount Vesuvius. Unlike tornadoes, which can happen virtually anywhere when conditions are favorable, volcanoes form when the Earth's tectonic plates pull apart or collide. More than half of the world's volcanoes can be found in an area known as the Pacific Ring of Fire. Although they are extremely dangerous, these forces of nature are actually quite beneficial to those who live near or even on them while they are dormant and quiet. In fact, many of the Earth's atmosphere and oceans were created from the gases released by erupting volcanoes. Volcanoes have also historically shaped our landscape through the development of mountains, islands, and plains. On average, 845 people die each year from volcanic hazards. The deadliest volcanic eruption, Mount Vesuvius in Italy, took place in 79 AD and killed 3,360 people due to the large amount of ash flows and falls.

What causes volcanic eruptions?

A volcanic eruption can be compared to the explosion one would get if you shook up a soda bottle. Unfortunately, volcanic formation is a lot more complex and gradual than this simple metaphor. To understand how a volcano forms, you must first have a good understanding of what lies beneath our feet.

The earth consists of three layers: the crust, the mantle, and the core. The crust is the thinnest layer and is broken into large pieces known as tectonic plates. These plates float on extremely hot magma which makes up the second layer, or the mantle. These plates move very slowly and are gradually changing the face of the Earth. Most volcanic eruptions and earthquakes occur along the edges of the boundaries of these plates because as these plates move, they are pushing, pulling away from, and bumping into the surrounding plates. When one plate slides beneath another, the result is a subduction zone. Rift zones are locations where plates begin to move apart and magma seeps up to the surface and erupts. Hotspots are volcanic locations that are not along plate boundaries. All of these so-called zones can be possible locations of volcanic activity.

A volcano erupts when the magma rises and builds up enough pressure to push through cracks in the Earth's surface known as vents and fissures. The magma, which is escaping from the magma chamber, is released along with a great amount of energy during a volcanic eruption, producing huge gas and dust clouds. The level of explosion depends on the amount of pressure within the volcanic structure and the consistency of the magma. After reaching the Earth's surface, magma becomes lava and steadily flows out of the volcano until the eruption is over.

Types of Volcanoes

Volcanoes are divided into groups based on their shapes, the material they consist of, and the way they erupt.

  • Composite Volcanoes: These volcanoes are formed by alternating layers of lava and rock fragments. They are characterized as having a "cone-like" shape and explosive eruptions. Mount Rainier is an example of a composite volcano.

  • Shield Volcanoes: These large volcanoes are built by many layers of runny lava flows. These volcanoes are usually the result of hot spots and their explosions are characterized by low-explosivity. Hot spots which develop in the ocean due to the spreading of the sea-floor are shield volcanoes. The Hawaiian Island volcanoes are perfect examples of shield volcanoes.

  • Cinder Cone Volcanoes: Distinguished by the formation of a steep conical hill above a vent, cinder cone volcanoes are the most common types of volcanoes in the world. However, their eruptions are low-key and are generally Strombolian eruptions. These volcanoes are built from cinders. These volcanoes live short lives but grow very rapidly.

  • Complex Volcanoes: This is the category applied to volcanoes whose features are a mixture of the various other types of volcanoes.

Types of Volcanic Eruption

Volcanoes are distinguished by the level of explosiveness during eruption.

  • Hawaiian- The least violent of all volcanic eruptions, this type of eruption is characterized by the gentle flow of lava from the volcanic vent. Occurring at hotspots, the lava is thin and runny and there is a low content of gases released. Very little, if any, volcanic ash is produced. This type of eruption receives its name from the Hawaiian Island volcanoes which historically display these characteristics. These eruptions result in gentle volcanoes known as shield volcanoes.

  • Strombolian- Named after the Italian volcano Stromboli, these eruptions are generally mild and occur regularly. Stromboli, located in the Aeolian Islands of Italy, has been erupting for centuries sporadically. These eruptions are generally characterized by short yet explosive eruptions of lava, usually ejected high into the air. Strombolian eruptions eject volcanic bombs, masses of molten rock, and lapilli. Mount Etna, in Italy, is also a very famous Strombolian volcano with eruptions occurring five times in the past three decades.

  • Vulcanian- Vulcanian eruptions are very violent explosions characterized by the release of thick lava and large lava bombs. Named after the volcano Vulcano, these eruptions give off large amounts of gas, ash, cinders, and pumice. These eruptions begin with a very noise explosion and the magma is expelled with large bangs. These eruptions can occur suddenly after a very dormant period.

  • Pelean- Pelean eruptions are named after the volcano Mount Pelee located in Martinique. The Mount Pelee explosion of 1902 was one of the worst natural disasters in history. These explosions feature a large amount of gas, dust, ash, and lava fragments which are violently blown out of the volcano's central crater. These eruptions can be detected by the growth of a lava spine, a bulge in the volcano's summit which signals the on-coming eruption. The lava released here is very sticky and thick.

  • Plinian- Plinian eruptions are the most violent types of eruptions. These eruptions are extremely dangerous as they usually occur very suddenly and unexpectedly because these volcanoes lay dormant for long periods of time. The large amount of volcanic material erupted into the air can cause climate changes. The gas and ash shoot upwards at a very high speed. Once the eruption ends, the area usually collapses and forms a caldera. These eruptions are named after the devastating eruption of Mount Vesuvius, which buried Pompeii and killed Pliny the Elder. The eruption of Mount St. Helens in 1980 was also characterized as a Plinian eruption.

Volcanic Explosivity Index (VEI)

VEI
DESCRIPTION
HEIGHT
VOLUME
CLASSIFICATION
HOW OFTEN?
0
Non-explosive
<100m
1000s m3
Hawaiian
Daily
1
Gentle
100-1000m
10,000s m3
Hawaiian/Strombolian
Daily
2
Explosive
1-5km
1,000,000s m3
Strombolian/Vulcanian
Weekly
3
Severe
3-15km
10,000,000s m3
Vulcanian
Yearly
4
Cataclysmic
10-25km
100,000,000s
m3
Vulcanian/
Plinian
10s of Years
5
Paroxysmal
>25km
1km3
Plinian
100s of Years
6
Colossal
>25km
10s km3
Plinian/
Ultra-Plinian
100s of Years
7
Super-Colossal
>25km
100s km3
Ultra-Plinian
1,000s of Years
8
Mega-Colossal
>25km
1,000s km3
Ultra-Plinian
10,000s of Years

Volcanic Aftermath

Most of the fatalities that occur during a volcanic eruption happen as a result of the events which follow the initial explosion. Volcanic eruptions can trigger mudflows and landslides, pyroclastic flows, tsunamis, and earthquakes.

Mudflows & Landslides:
Because most volcanoes are located in mountainous regions, the peaks are usually covered by ice and snow and are found at very high elevations. After a volcanic eruption, the lava and hot gasses melt the snow and ice, causing it to slide down the side of the mountain at a very rapid pace. As it travels down, the melted ice and snow, which is now extremely hot water, picks up dirt and debris on the way down. (Link to the Landslide page for more information)

Pyroclastic Flows:
Large debris and gas is emitted during a volcanic eruption. When the Earth's gravity pulls this hot cloud of rock debris and gas down the side of the volcano, it is referred to as pyroclastic flow. This is one of the most dangerous effects of a volcanic eruption because these gases are superheated and can travel at speeds as high as 450 mph. This flow can extend for miles beyond the base of the volcano, creating a danger for those who live in surrounding areas.

Tsunamis:
When volcanoes are located near large bodies of water, such as those located in the Pacific Ring of Fire, they can easily trigger tsunamis. When volcanoes erupt, the landslides that accompany the eruption displace large sections of the volcano. These large sections can fall into the surrounding water, which causes a large amount of water to be displaced and potentially generate tsunami waves. Tsunami effects are usually felt when underwater volcanoes explode. Water is forced upward at a very high pace and creates displacement waves which travel towards the nearest landmasses.

Earthquakes:
Earthquakes are typically a precursor of a volcanic eruption but some can occur afterwards as well. The movement of magma is the general cause of all volcanic related eruptions because it creates fluctuations in pressure.



Facts about Volcanoes

  • Areas downwind of a volcano are the most dangerous so avoid this area as much as possible.

  • Wear long-sleeve shirts and pants in order to protect your legs and arms.

  • If you become trapped in your car during an eruption, turn off the engine

  • As fascinating and attention-grabbing as volcanic eruptions are, they are not safe! Leave the area of an eruption as soon as possible and as safely as possible.

  • If your neighbors aren't as prepared or are in need of help, be willing to assist them and share your supplies to ensure their safety.

  • Active volcanoes in the U.S. are found mainly in Hawaii, Alaska and the Pacific Northwest. The danger area around a volcano covers approximately a 20-mile radius however some danger may exist 100 miles or more from a volcano.

  • Sideways directed volcanic explosions, known as "lateral blasts," can shoot large pieces of rock at very high speeds for several miles. These explosions can kill by impact, burial or heat. They have been known to knock down entire forests.

  • Volcanic ash can affect people hundreds of miles away from the cone of a volcano.

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